MSK Flashcards

Question

A 17-year-old patient complains of lower thoracic back pain. Plain radiographs of the thoraco- lumbar spine show wedging of multiple vertebrae at the thoraco-lumbar junction, multiple limbus vertebrae, an increase in the AP diameter with a reduction in the sagittal height of multiple vertebrae, and multiple endplate defects. What is the unifying diagnosis? [B2 Q31] a. Scheuermann’s disease b. Ankylosing spondylitis c. Mycobacterium tuberculosis d. Hyperparathyroidism e. DISH

Answer 1

**Scheuermann’s disease** These are the classical appearances of Scheuermann’s disease. This condition usually presents at puberty and consists of: **Vertebral wedging** **Endplate irregularity** **Narrowing of the intervertebral disc spaces** The most common location is in the lower thoracic and upper lumbar spine. Schmorl’s nodes are often present.

Answer 2

**Osteoporosis** Osteoporosis is a feature of homocystinuria and occurs in 75% of cases, often causing bowing and fracture of the long bones. The other features are all more suggestive of Marfan’s syndrome. Although arachnodactyly does occur in homocystinuria (in 30% of cases), it occurs in 100% of people with Marfan’s syndrome. Homocystinuria has an autosomal recessive mode of inheritance

Answer 3

**Scleroderma** The other causes of loss of the lamina dura include Cushing’s disease, Paget’s, hyperparathyroidism, osteoporosis, osteomalacia, leukaemia, metastases and Langerhans’ cell histiocytosis. Both osteopetrosis and hypoparathyroidism cause thickening of the lamina dura of the teeth.

Answer 4

**Scleroderma** Scleroderma is the cutaneous manifestation of progressive systemic sclerosis. This causes fibrosis and small vessel disease in several organs. In the hands, typically it causes terminal phalangeal resorption due to pressure atrophy, soft tissue calcification and occasionally intra- articular calcification.

Answer 5

**Caffey disease** The most likely diagnosis is Caffey disease. This is a relatively rare self-limiting condition which usually presents before six months of age. The mandible is the most common site and accounts for 80% of cases, followed by the clavicle and the upper limb bones.

Answer 6

**Tuberous sclerosis** This is a multi-system autosomal dominant disorder affecting the central nervous system, kidneys, lung and heart. The classic triad of facial angiofibroma, epileptic seizures and mental retardation is only seen in approximately 30% of patients. Skeletal abnormalities in TS include: **sclerotic calvarial patches or ‘bone islands’** **Thickening of diploe** **Expansion and sclerosis of ribs** **Periosteal thickening of long bones.** Gracile ribs are often seen in association with Down’s syndrome.

Answer 7

**Heterozygous achondroplasia** Patients with pseudoachondroplasia have a normal skull and medial beaking of the proximal femoral neck. Achondrogenesis is lethal in utero/neonatal period, as is homozygous achondroplasia. In metatrophic dwarfism, dumbbell shaped long bones and flattened vertebra may be found

Answer 8

**Melorheostosis**. The radiographic ﬁndings describe the **‘ﬂowing candle-wax’** sign **(continuous, irregular cortical hyperostosis in a long bone)**, which indicates melorheostosis, a non-hereditary sclerosing bone dysplasia of unknown aetiology. Patients are often asymptomatic, being discovered incidentally. It is most common in the long bones. The disease can overlap with other sclerosing bone dysplasias such as: **Osteopoikilosis (multiple ovoid bone islands)** **Osteopathia striata (metaphyseal longitudinal striations).** Engelmann disease presents in childhood with neuromuscular dystrophy. Diaphyseal fusiform enlargement with cortical thickening is seen in the long bones. Fibrous dysplasia causes bone thinning.

Answer 9

**Atlanto-axial instability** Achondroplasia is the most commonly seen autosomal dominant rhizomelic dwarﬁsm. Rhizomelia refers to relative shortening of the proximal compared with the distal portion of the limbs. Achondroplasia has widespread skeletal manifestations affecting the skull, chest, spine, pelvis and extremities. Intelligence and motor function are normal. The most signiﬁcant complication is brain-stem or spinal cord compression due to spinal stenosis, which is caused by alignment abnormalities and decreased spinal canal size due to short pedicles with a reduced interpedicular distance. Atlantoaxial instability is deﬁned as a predental space of 3 mm or more in adults and 5 mm or more in children, or where there is considerable change between ﬂexion and extension. It is seen in inﬂammatory arthritides, in Down’s and Morquio’s syndromes, and with retropharyngeal abscess in a child.

Answer 10

**Proximal scaphoid pole** Osteonecrosis may be caused by two mechanisms: interruption of arterial supply, and intra- or extra-osseous venous insufﬁciency. Interruption of vascular supply is usually associated with a fracture, as seen in the proximal scaphoid following waist fractures. Femoral head osteonecrosis can occur with subcapital fractures, or without fracture as in Legg–Calve´– Perthes disease. Other common locations that may develop osteonecrosis without overt fracture include the medial tibial condyle (Blount’s disease), metatarsal head (Freiberg’s infraction) and the lunate (Kienbock’s disease). Radiographic ﬁndings often lag several months behind the injury or onset of symptoms, and MR is the most sensitive imaging modality. Radiographic signs include focal radiolucencies, sclerosis, bone collapse and loss of joint space

Answer 11

**Gaucher’s disease** Marrow reconversion is the repopulation of yellow (fatty) marrow with haematopoietic cells, reconverting the fatty marrow to red marrow. This occurs when the haematopoietic capacity of the existing red marrow in an adult is insufﬁcient. This can result from increased physiological requirement (long distance running), chronic anaemia (sickle cell disease) and chemotherapeutic treatment with granulocyte–macrophage colony-stimulating factor. The pattern of reconversion is predictable and it is the reverse of the age-related physiological conversion of red to yellow marrow. **Reconversion begins in the axial skeleton and progresses distally through the appendicular skeleton, to end in the hands and feet.** Knowledge and recognition of this pattern are important because neoplastic inﬁltration of adult yellow marrow in malignant disease may have similar MR appearances. However, malignant marrow replacement tends to have a more random distribution than reconversion; it may enhance with intravenous gadolinium, can cause cortical destruction and may extend into the soft tissues.

Answer 12

**Use fast spin echo (FSE) imaging rather than GE imaging**. Magnetization of the implant affects the local ﬁeld gradient, proton dephasing, and spin frequency, resulting in signal void, spatial distortion, and spurious high signal. The lack of a 180° rephasing pulse in GE sequences, as opposed to SE/FSE sequences, means that T2* effects are not reversed, and a greater dephasing of spins occurs in GE than in SE/FSE techniques. Thus, GE techniques have a greater sensitivity to magnetic susceptibility effects. This is detrimental when imaging patients with metal prostheses, but can be used to advantage in certain clinical situations, e.g. when identifying subtle haemorrhage due to the magnetic susceptibility effects of iron in haemosiderin (a blood breakdown product)

Answer 13

**Kidneys** A super-scan refers to a99m Tc-labelled technetium IBS where there is **diffuse increased osseous uptake** with apparent **reduced renal and soft tissue uptake**. The appearance is commonly due to widespread osteoblastic bony metastases (e.g. **prostate or breast carcinoma**), but is also caused by non-malignant disease (e.g. **renal osteodystrophy, hyperparathyroidism, osteomalacia, myeloﬁbrosis, Paget’s disease**). In metastatic disease there is usually higher uptake in the axial than the appendicular skeleton. In IBS uptake is normally seen in bone, kidneys, and bladder, soft tissues (low levels), breasts (particularly in young women), and epiphyses (skeletally immature patients). Uptake is seen in the myocardium (high), brain (high), and bowel (moderate) in FDG-PET scanning, not IBS; however myocardial uptake on IBS can be seen in cases of recent myocardial infarction and amyloidosis. Note that poor renal function can often demonstrate reduced or absent renal visualization producing an appearance like a superscan (false positive), whereas urinary tract obstruction in prostatic carcinoma can increase renal activity and lead to false negative scans.

Answer 14

**T2 coronal** The best sequence would be a T2 or T2* image for detecting a tear. This is also a useful plane in which to assess for ulnar variance; positive ulnar variance has an association with perforations. The central portion of the articular disc is not well vascularised and therefore a tear in this portion will heal poorly. The peripheral portion, however, has been vascularised.

Answer 15

**The MRI ﬁndings correlate well with the severity of ﬁndings on plain ﬁlm radiography**. MRI has been shown to correlate well with the severity of OA as depicted on plain ﬁlm radiography. Neither MRI nor plain ﬁlm appearances are signiﬁcantly associated with the patient’s symptoms.

Answer 16

**The MRI ﬁndings correlate well with the severity of ﬁndings on plain ﬁlm radiography**. MRI has been shown to correlate well with the severity of OA as depicted on plain ﬁlm radiography. Neither MRI nor plain ﬁlm appearances are signiﬁcantly associated with the patient’s symptoms.

Answer 17

**Grade 1 osteophytosis in the knee**. While the Kellegren and Lawrence grading of OA is the most widely used scale for grading OA on plain ﬁlms, early osteophyte formation is not deﬁnitively ‘arthritic’ change. Studies have shown that patients with this type of early change infrequently progress to developing more severe disease. Recent research in OA is focused on the impact of the subchondral bone on the disease, rather than hyaline cartilage. This is evidenced by increased uptake on bone scan being closely linked to progressive OA, even in patients with relatively normal joints on plain ﬁlm. The foci of high signal on T2WI and STIR are bone marrow lesions that if persistent can indicate pathology in the subchondral bone, which can lead to arthritic change. The serpiginous line describes the classical ﬁnding of avascular necrosis. Both this and osteochondral defects lead to progressive OA change.

Answer 18

**Erosive OA**. If the presence of erosions is ignored the pattern of disease is typical of OA. Erosive, or inﬂammatory, OA shows typical OA distribution, but with central erosions in the affected joint spaces in the distal IP, and less commonly proximal IP, joints. These central erosions in combination with marginal osteophytes give the classical gull-wing appearance to affected joints. Whilst individual joint appearance can be identical to psoriatic arthropathy, which can precede the development of the skin disease, the overall pattern is atypical, making it less likely. Also, while the distribution of CPPD arthropathy is often identical to OA, it would not cause erosions, and would usually be associated with chondrocalcinosis.

Answer 19

**Erosive osteoarthritis** Central articular erosion with a ‘seagull’ pattern, ankylosis and periarticular osteoporosis is typical of erosive osteoarthritis. This is seen in older women and is usually limited to hands, particularly affecting the proximal interphalangeal joints.

Answer 20

**The presence of hypothyroidism is associated with the diagnosis**. Disorders associated with CPPD are the four Hs: Hyperparathyroidism Haemochromatosis Hypothyroidism Hypomagnesaemia. Use of nomenclature in this disorder is confused. Pseudogout is the clinical presentation of an acutely inﬂamed joint due to calcium pyrophosphate crystal deposition, and as such is not a radiological diagnosis. Pseudogout syndrome is the dominant feature in only 10–20% of cases of CPPD. Another 10–20% of cases are asymptomatic, whilst most present with symptoms identical to OA, with occasional ﬂares. Disproportionate involvement of the patellofemoral joint is a characteristic feature but is only occasionally seen. Pyrophosphate arthropathy is a description of the pattern of disease present due to crystal deposition, and as such is not a diagnosis made by analysis of joint aspirate.

Answer 21

**Gouty arthritis** **Periarticular erosions** **sclerotic borders** **overhanging margins** **preserved articular surface** Rheumatoid arthropathy has non-proliferative marginal erosions, symmetrical distribution and joint space narrowing. Psoriasis show progressive joint destruction with erosions. Erosive osteoarthritis is symmetrical with erosions are in the centre of the articular surface. Calcium pyrophosphate deposition disease is polyarticular, and shows chondrocalcinosis and joint-space narrowing.

Answer 22

**Psoriatic arthropathy**. Bone involvement before skin changes is evident in up to 20% of cases. Nail pitting or discolouration is common and correlated with the severity of the arthropathy. Five distinct manifestations have been described: oligoarthritis, polyarthritis (predominately distal IP joints), symmetric type (resembling RA), arthritis mutilans, and spondyloarthropathy. The characteristic distribution involves the small joints of the hands and feet, with or without spondyloarthropathy. Involvement in the hands tends to include distal IP as well as MCP or PIP joints, with early tuft resorption and distal IP erosive disease. The erosions become so severe that a ‘pencil-in-cup’ deformity and telescoping of the joint may occur. Bone density can be normal, and the joint distribution is asymmetric. Similarly, sacroiliitis is asymmetric, unlike ankylosing spondylitis and syndesmophytes, which are non-marginal and asymmetric; in ankylosing spondylitis they are marginal and asymmetric. The spondyloarthropathy of psoriatic arthropathy is indistinguishable from that of reactive arthritis, the clinical scenario (rash vs uveitis/urethritis) providing the diagnosis. The arthropathies of CPPD disease and haemochromatosis are essentially identical radiographically. Chondrocalcinosis is commonly seen in the wrist (triangular ﬁbrocartilage) and knee (menisci). The joints most affected are the knee, wrist and second and third MCPs of the hand: the IP joints tend to be spared. Early disease shows erosive change. More advanced disease demonstrates sclerosis, osteochondral fragments, and osteophytes. Subchondral cysts are common and large. RA is rarely found in the distal IP joints and periosteal reaction is not a feature. SLE is usually non-erosive and affects the MCP joints.

Answer 23

**SAPHO syndrome**. The most common presentation for this condition is acne and palmoplantar pustulosis with changes in the sterno-costoclavicular region where hyperostosis is seen, often with some erosive change. The condition can also cause several manifestations in the spine, ranging from focal hyperostosis of one or more lumbar vertebrae, to a syndrome strikingly like psoriatic spondylo-arthropathy. In the appendicular skeleton hyperostosis is commonly seen. SAPHO can also give rise to manifestations identical to osteomyelitis, but with no causative organism. In this respect there is overlap with CRMO syndrome. Patients are frequently human leucocyte antigen (HLA) B27 positive, and psoriasis frequently coexists, leading some authors to suggest that SAPHO is a variant of psoriatic arthropathy, although this is not widely accepted.

Answer 24

**SAPHO syndrome** **Synovitis, acne, pustulosis, hyperostosis and osteitis**. (SAPHO) syndrome is a term encompassing several disease entities that demonstrate an association between rheumatological and cutaneous lesions. There may be a delay of several years between the onset of osseous symptoms and cutaneous manifestations. It is thought to be similar to chronic recurrent multifocal osteomyelitis in children. The dominant radiographic abnormality is new and bizarre bone proliferation, with the sternoclavicular joint affected in 70–90% of cases.

Answer 25

**Bony ankylosis of the carpal bones**. Whilst ﬁbrous ankylosis of the carpal and tarsal bones does occur, bony ankylosis is extremely rare in RA. It is, however, common in JRA. There are a number of unusual ﬁndings, which if present should indicate a diagnosis other than RA. Productive bone change (e.g. periostitis or enthesopathy) is extremely unusual. Osteophytes are also uncommon in the absence of advanced associated osteoarthritic change. The exception to this is the distal ulna, a feature known as ulnar capping. The other features are all typical of RA.

Answer 26

**Hyper-vascular pannus at the TFCC and RUJ, with joint effusion at DRUJ**. Hyper-vascular pannus is intermediate to high signal on T2WI and low signal on T1WI. It also enhances, retaining enhancement on delayed imaging. Joint effusions can be difﬁcult to differentiate from hyper-vascular pannus on pre-contrast imaging. Following enhancement, they show only delayed enhancement. Fibrous pannus is low signal on all sequences.

Answer 27

**HIV-associated arthritis**. This is oligoarticular, asymmetric and peripheral. It primarily affects the knees and ankles. It has a short duration of 1–6 weeks; radiography may reveal a joint effusion. Acute symmetric polyarthritis also occurs in HIV. It behaves clinically like RA, but patients are negative for rheumatoid factor. Features that help differentiate it from RA are periostitis and proliferative new bone formation. Occasionally an erosive variety with little or no proliferative bone formation occurs. Psoriatric arthritis has a higher prevalence among AIDS patients than in the general population. HPOA is associated with P carinii pneumonia (PCP) in AIDS. Plain ﬁlms reveal periosteal reaction. Kaposi’s sarcoma uncommonly affects the bone but does so most commonly in Africa. Non- Hodgkin lymphoma (NHL) is the second most common tumour in HIV infection. It can produce lytic, sclerotic, or mixed lesions with a wide zone of transition; they are usually lytic. Other musculoskeletal complications in AIDS include infections (cellulitis, osteomyelitis, septic arthritis, pyomyositis, necrotising fasciitis), Reiter’s syndrome, undifferentiated spondyloarthropathy, polymyositis, osteonecrosis (especially of the femoral head), osteoporosis, rhabdomyolysis, and anaemia.

Answer 28

**Ankylosis involves the vertebral edges or centre**. The question refers to ankylosing spondylitis. Ankylosis involves the vertebral edges or centre, with bony extension through the disc. The former is thought to be secondary to a Romanus lesion, the latter an Andersson lesion. Romanus lesions are irregularities and erosions involving the anterior and posterior edges of the vertebral endplates and are the earliest changes of spondylitis depicted on conventional radiographs. On MRI an Andersson lesion is depicted as disc-related signal-intensity abnormalities of one or both vertebral halves of a discovertebral unit. They are often hemispherically shaped. MRI is better than conventional radiography at depicting Romanus lesions, Andersson lesions (spondylodiscitis), and most other abnormalities, although ankylosis is equally well detected by both modalities. Syndesmophtyes are difﬁcult to detect on MRI. Plain radiography is superior in this respect because of its superior spatial resolution; syndesmophtyes are seen as bony outgrowths of the anterior vertebral edges. They occur in 15% of the vertebrae of patients. Apical pulmonary ﬁbrosis affects 1% of patients. Sacroiliac (SI) joint erosion and widening is an early feature, and this may initially be more prominent on the iliac side of the joint, as the cartilage on that side is normally thinner. Later in the disease, sclerosis and ankylosis occur and the SI joints become symmetrically fused. Enthesitis is most prominently seen when the interspinal ligaments, those that extend between the spinous processes, and the supraspinal ligaments are affected. Ligamentous involvement is characterized by an increased signal intensity on either STIR images or contrast-enhanced T1WI fat saturated sequences. It may be associated with osteitis of adjacent bone marrow in the spinous processes. Arthritis of the synovial joints (e.g. facet joints) and insufﬁciency fractures (often spontaneous or after minor trauma) are also features of the seronegative spondylarthritides.

Answer 29

**Psoriatic arthritis.** Ankylosing spondylitis causes a symmetrical sacroiliitis. The syndesmophytes associated with this are marginal and ﬁne. It also typically progresses superiorly from the lumbar spine. Both reactive arthritis and psoriatic arthritis cause an asymmetric sacroiliitis and the syndesmophytes are usually centred on the thoracolumbar spine and are non-marginal and bulky. Retrocalcaneal bursitis and erosions, whilst more common in reactive arthritis, can occur in psoriatic arthritis, and reactive arthritis would uncommonly affect the hands. Also, with all other factors being equal, psoriatic arthritis is much more common than reactive arthritis, even without the skin manifestations, which are absent in up to 20% at presentation.

Answer 30

**Reiter’s syndrome** Reiter’s syndrome is the association of urethritis, conjunctivitis and mucocutaneous lesions. Sacroiliitis is usually bilateral but often persists asymmetrically. There is an association with the HLA B27 antigen. Reiter’s has a predilection for the great toe and metatarsophalangeal joints.

Answer 31

**Rheumatoid arthritis** Myeloma, hyperparathyroidism, metastases, cleidocranial dysplasia and Gorlin basal cell nevus syndrome all cause absence of the outer end of the clavicle. Destruction of the medial end of the clavicle is caused by metastases, infection, lymphoma, eosinophilic granuloma, rheumatoid arthritis, and sarcoma.

Answer 32

**Juvenile rheumatoid arthritis** The condition is usually seen in young people before the age of 16 years. In the hand, the metacarpophalangeal and interphalangeal joints are usually affected. Chronic synovitis causes enlargement of bones and epiphyses. Malalignment and subluxation are common. An important feature of juvenile arthritis is periosteal reaction affecting the metacarpal and phalangeal shafts.

Answer 33

**Psoriatic arthritis** This is usually HLA B27 positive and is associated with skin and nail changes in most cases. The hands are often described as having sausage digits, and erosions with ill-defined margins are characteristic. Sacroiliitis is often present and most often bilateral. Within the axial skeleton, there is often large bulky vertically orientated soft-tissue ossification giving a ‘floating’ osteophyte appearance.

Answer 34

**E** The remaining answers are also seen in TB arthritis. Even and thin synovium, large bone erosions, rim enhancement around bone erosion and extra-articular cystic masses are more frequently seen in TB arthritis

Answer 35

**Psoriatic arthritis** Hands are more commonly affected in psoriatic arthropathy, whereas feet are more commonly affected in Reiter’s

Answer 36

**Hyperextension of DIP J and flexion of PIP J** A-D are features seen in SLE.

Answer 37

**New bone formation** is the hallmark ﬁnding of psoriatic arthritis and is not seen in rheumatoid arthritis. Conversely, periarticular osteoporosis is seen in rheumatoid but is not a feature of psoriatic arthritis. Both conditions may cause soft tissue swelling (typically a sausage digit in psoriatic arthritis), joint space loss and erosions, which are marginal in psoriatic and marginal and/or central in rheumatoid arthritis. Another distinguishing factor is the distribution of involved joints in the hands, which is typically, but not always, interphalangeal in psoriatic and metacarpophalangeal in rheumatoid arthritis.

Answer 38

**Osteoporosis** CREST syndrome represents the limited form of the autoimmune connective tissue disorder scleroderma. Five-year survival rate is 50–67%. The two other types of sclerodermas are generalized (also called systemic sclerosis) and localized (morphoea). Common ﬁndings are digital soft-tissue oedema with sclerodactyly (tapered soft tissues), acro-osteolysis (autoamputation) and calcinosis. There may be associated arthritis that shows erosions (also seen in the ribs) or terminal phalanx resorption, with joint space narrowing a late sign. Osteoporosis is not usually a feature except in the context of disuse.

Answer 39

**Para-syndesmophytes** Seronegative spondyloarthritis is an umbrella term for inﬂammatory joint or spinal conditions that are not associated with rheumatoid factor or rheumatoid nodules. There are ﬁve described subgroups: ankylosing spondylitis, psoriatic arthritis, arthritis associated with inﬂammatory bowel disease, reactive arthritis (e.g. Reiter’s syndrome) and an undifferentiated subgroup. The subgroups may overlap both clinically and radiologically, and the diagnosis is more easily made based on clinical history and examination. Imaging plays a limited role in differentiation, particularly early in the disease when there can be considerable overlap of appearances. The main exception is the identiﬁcation of para-syndesmophytes, which are seen almost exclusively in psoriatic arthropathy. In addition, bone marrow oedema can involve the entire vertebral body in psoriatic arthritis, which may be a further useful distinguishing feature. Undifferentiated spondyloarthritis is diagnosed when there is no clinical or radiological evidence of sacroiliitis. All types may eventually progress to ankylosis.

Answer 40

**Protrusio acetabuli** Even or eccentric joint space reduction representing cartilage loss is seen in both types of arthritis and not a distinguishing diagnostic feature. Although osteoarthritis is said to be classically eccentric, this is difﬁcult to assess accurately on many hip radiographs, as they are not routinely taken in the upright, weight-bearing position. Subchondral sclerosis and cysts are typically associated with degenerative osteoarthritis. Although soft-tissue swelling is a feature of rheumatoid arthritis, the depth of the hip joint and the copious surrounding soft tissues mean that any synovial swelling is unlikely to be appreciated clinically or radiologically. Subtle osteophytes (in osteoarthritis) or erosive change/osteoporosis (in rheumatoid arthritis) can distinguish between the two entities. An inﬂammatory cause should be considered in young adults with hip pain and, if protrusio or other abnormalities are found, the sacroiliac joints should be examined

Answer 41

**Amyloidosis**. There are a lot of conditions that are capable of mimicking RA. In these cases, a few key features can help reach a diagnosis. The classic ﬁnding in gout is of non-marginal erosions, as opposed to those described. Nevertheless, marginal erosions can occur with gout. An RA-type picture in the presence of non-marginal erosions or calciﬁed soft-tissue nodules (tophi) should suggest this diagnosis. CPPD gives a more productive pattern of arthritis, such as seen with OA, affecting the radio-carpal joint. Thus, it is often suspected when the appearance is of OA with a ‘funny distribution’. Amyloidosis is suggested ﬁrst by the history of MM. Involvement of the hands is more commonly seen in amyloid secondary to prolonged dialysis but can be seen when the amyloid is secondary to MM, when the wrists are often affected. Amyloid can closely resemble RA in its distribution and the pattern of erosions. However, three important features can help differentiate: amyloidosis classically preserves the joint space, is not usually associated with periarticular osteopenia, and amyloidosis causes well-demarcated subchondral cyst formation in excess to that expected from the degree of joint disease.

Answer 42

**B**. Multiple sites can be involved and there is characteristic preservation of joint spaces

Answer 43

**Hook like osteophytes on the radial aspects of the metacarpal heads** Although all the answers are features, hook-like osteopohytes are the most characteristic. Arthropathy is seen in 50%, and chrondrocalinosis in more than 60%, with knees being most commonly affected.

Answer 44

**Metacarpal hooked osteophytes** Haemochromatosis is excess iron deposition in the tissues and can be either primary (autosomal recessive genetic disorder) or secondary to ineffective erythropoiesis or iron overload. Skeletal manifestations include osteoporosis (which is proportional to the extent of iron deposition), small subchondral cysts, arthropathy (50%), concentric joint space narrowing, chondrocalcinosis, and characteristic hooked osteophytes on the radial aspect of the metacarpal heads. Other organs can be affected by iron deposition, most commonly the brain, liver, pancreas and spleen

Answer 45

**Wide zone of transition** The zone of transition relates to the interface between the tumour margin and the host bone. It is an extremely important discriminator, particularly for lytic lesions. Lesions with a well- deﬁned margin (and therefore narrow zone of transition) are described as geographic and are usually non-aggressive, whereas those with a wide zone of transition are termed ‘permeative’ and are often malignant or aggressive (such as in osteomyelitis). Cortical expansion without destruction is seen in many benign or slow-growing conditions such as ﬁbrous cortical defect and aneurysmal bone cyst. Many bone lesions, both benign and aggressive, are lytic. Periosteal reaction does not indicate an aggressive lesion as such, but the pattern of reaction can do so. Multiplicity is not an indicator of malignancy, as it can be seen in benign and self-limiting processes (such as multiple enchondromatosis and neuroﬁbromatosis). Equally, a solitary lesion may be malignant

Answer 46

**Soap-bubble** Periosteal reactions are usually a radiographic manifestation of underlying bone disease. The term ‘soap bubble’ refers to expansion of the cortex without destruction by a lytic bone lesion. The intact cortex usually indicates a benign process, whereas cortical destruction is associated with malignant or aggressive lesions. Sunray and hair-on-end reactions are spiculated forms of periosteal reaction that occur following periosteal elevation by tumour, with tumour preventing the subperiosteal space from ﬁlling with new bone. Laminated or ‘onion-skin’ reaction occurs with both malignant and benign processes and indicates an intermittent or cyclical process. Codman’s triangles are formed by elevation and then destruction of the periosteum. They are usually related to malignant tumours but can also be formed by aggressive benign processes.

Answer 47

**Cartilaginous** Chondroid tumour matrix may or may not calcify, but, if it does, the pattern is characteristically in arcs or circles and is sometimes described as ‘popcorn’. Osteoid matrix when calciﬁed is usually dense and homogeneous like a cloud. Calciﬁed ﬁbrous matrix has a characteristic ground-glass appearance, whereas a cellular tumour usually does not show matrix calciﬁcation. A mixed matrix will show mixed characteristics.

Answer 48

**Osteopoikilosis** Osteopoikilosis is a rare condition causing multiple enostoses (bone islands), which are asymptomatic and usually of no clinical signiﬁcance. They represent deposits of normal cortical bone within the cancellous bone. Osteopathia striata (Voorhoeve’s disease) is similar to osteopoikilosis in appearance and is usually asymptomatic, but it consists of linear longitudinal or sunburst striations rather than rounded densities. Osteopetrosis causes generalized increase in bone density, whereas melorrheostosis is a cortical process giving a ‘ﬂowing wax’ appearance, usually affecting only one side of the affected bone. While metastases are plausible, the patient would probably be symptomatic and have evidence or a history of a primary tumour

Answer 49

**Osteoid osteoma** This most commonly presents in the second and third decades. The male: female ratio is 2.5:1. Classically it presents with increasing pain which is worse at night and often relieved with aspirin. Spinal lesions often lead to painful scoliosis. Almost any site in the body may be affected but the most common regions are the lower limb and spine

Answer 50

**Osteoid osteoma** This typically presents as a small lytic lesion with central mineralisation surrounded by reactive sclerotic area. On bone scans, the central nidus shows intense uptake surrounded by region of lesser activity (double density sign). MRI demonstrates bone oedema pattern and typically relieved with aspirin. Stress fractures are transverse and linear. Ewing’s sarcoma and infection must be considered if soft tissue involvement is seen on MRI.

Answer 51

**Most found in long bones of the lower limbs** Although osteoid osteomas can occur in any bone, they are most common in the metadiaphyseal femur and tibia. The nidus appears lucent on radiographs, intensely active on bone scan – with surrounding well-defined luceny (double doughnut sign), isointense to muscle on T1 and variable SI on T2

Answer 52

**Osteoma** The best diagnostic clue is the densely sclerotic, well-defined lesion attached to the parent bone. Latent lesions show no tracer uptake

Answer 53

**Osteoid osteoma** Osteoid osteoma accounts for 12% of benign neoplasms of bone. It is most located in the cortex of long bones (50% in the femur and tibia) with 15% in the spine, typically the pedicle. It rarely exceeds 15 mm in size. Young men are most affected, with pain as the predominant presenting feature due to the extensive inﬂammatory reaction and vascularity of the lesion. With spinal lesions this results in a painful positional scoliosis, though most patients experience improvement of the pain with salicylates. The lucent central area or nidus represents the underlying pathological process, with the surrounding sclerosis representing reactive inﬂammatory change in normal bone. Treatment traditionally was surgical curettage, but radiologically guided percutaneous radiofrequency ablation is now used.

Answer 54

**Complete symptom relief is seen in 90% after initial therapy**. Osteoid osteoma is a benign, but painful, bone tumour typically found in the lower limbs of children and young adults. The use of CT-guided RFA is a safe and effective technique and is the treatment of choice over open surgical approaches. Complete relief of symptoms is observed in approximately 90% after initial therapy and is reported up to 100% for secondary procedures. The procedure is performed under general or spinal anaesthesia. A typical clinical history of night pain relieved by non-steroidal analgesia and radiographic features of the central nidus are considered sufﬁciently diagnostic to proceed with RFA. The procedure should not be performed if there are doubts regarding diagnosis. Osteomas within the spine are potentially treated by RFA if the nidus is >1 cm from the dura/neural structures. Since most spinal osteomas are located within the posterior elements, however, RFA is generally unsuitable.

Answer 55

**Osteoblastoma**. Osteoblastoma is similar both clinically and histologically to osteoid osteoma, but there are some differences that aid in distinguishing these two entities. **Clinically osteoblastoma is typically less painful** than osteoid osteoma and **does not respond as well to Aspirin**. An osteoblastoma in the neural arch of the spine is more likely to cause neurological signs, as these lesions are typically larger and more expansile than osteoid osteoma. The lucent nidus seen in osteoid osteoma is usually less than 1.5–2 cm in size, whereas the **nidus in osteoblastoma is usually larger than 2 cm** at diagnosis and has less surrounding sclerosis. The nidus may or may not have a calciﬁc focus within, in both these diagnoses. The appearance described in the question is the subgroup of osteoblastoma that has similar features to osteoid osteoma. Other appearances on imaging of osteoblastoma include an expansile lesion with multiple small calciﬁcations and a peripheral sclerotic rim or, more rarely, an aggressive appearance with osseous expansion, bone destruction, inﬁltrating soft tissue, and intermixed matrix calciﬁcation. An enostosis (or bone island) may be giant (greater than 2 cm) but should be well deﬁned and densely sclerotic. It is possible a bone abscess could cause a lytic lesion with surrounding sclerosis, but the patient is systemically well, making infection less likely. A bone abscess is also unlikely to be as expansile as the lesion described. Intracortical haemangioma is a very rare diagnosis, usually within the cortex of a long bone, such as the tibia. On CT there is a hypoattenuating lesion, with spotty internal calciﬁcation or a ‘wire-netting’ appearance.

Answer 56

**Osteoblastoma** Also called giant osteoid osteoma when measuring > 2 cm. Osteoid osteoma are < 2 cm, have a predilection for the axial skeleton and usually respond to salicylates. Osteosarcomas show cortical destruction, mineralised matrix, and soft tissue mass. Aneurysmal bone cysts show fluid–fluid levels and no matrix calcification.

Answer 57

**Osteoblastomas** Osteoblastomas share clinical and histological features with osteoid osteomas and 3-12% occur in ribs.

Answer 58

**Bizarre paraosteal osteo-chondromatous proliferation** Bizarre paraosteal osteochondromatous proliferation (also known as Nora’s lesion) is a rare condition usually seen in adults in the third and fourth decades of life. Osteochondroma-like lesions are seen most at the proximal and middle phalanges, followed by the metacarpals and metatarsals. A relationship to trauma has been suggested but not proven. Other locations that may be affected include the long bones (especially those of the upper extremity), skull and jaw. It is thought to be a similar process to that which gives rise to lesions in myositis ossiﬁcans, reactive periostitis and subungual exostosis. On plain radiographs, a well-deﬁned bony mass is seen attached to the surface of the parent bone. Features differentiating this from

Answer 59

**Osteosarcoma** The **telangiectatic variety of osteosarcoma does show ﬂuid–ﬂuid levels**, as does malignant ﬁbrous histiocytoma or any necrotic bone tumour. Telangiectatic osteosarcoma is highly vascular and contains necrotic tissue and blood, with tumour located only along the periphery and septa. MRI will thus reveal enhancing nodularity in the latter locations; this ﬁnding will be absent in the case of ABC or GCT. In addition to those mentioned in the stem, the plain ﬁlm ﬁndings include bone expansion and cortical breakthrough. Unlike the other lesions, osteoblastoma does not demonstrate ﬂuid–ﬂuid levels on MRI; it is more common in the posterior elements of the spine than in the long bones. **ABC, GCT, and chondroblastoma have a narrower zone of transition** on plain ﬁlm than telangiectatic osteosarcoma. **GCT is subarticular.** **Chondroblastoma is epiphyseal**

Answer 60

**Telangiectatic osteosarcoma** With the MRI finding described, the most likely explanation is that the lesion is a telangiectatic osteosarcoma. This is a rare type of osteosarcoma with a mean age at presentation of 20 years. The most common site is around the knee (62%). Fluid-fluid levels are also seen in giant cell tumours and aneurysmal bone cysts.

Answer 61

**Presence of osteoid matrix with septal regions on CT** Thick peripheral septa with nodularity, presence of an osteoid matrix within nodular or septal regions, and aggressive growth features such as cortical destruction indicate TOS rather than ABC.

Answer 62

**T3 N0 M1a** Complete staging of primary bone sarcomas is unusual in that it also incorporates the histological staging once tissue diagnosis via biopsy or surgical resection is available. The local TNM classiﬁcation is T1 (single lesion less than 8 cm), T2 (single lesion over 8 cm) or T3 (skip lesions of any size). Nodal staging is N0 (no nodes) or N1 (any number of metastatic nodes). Metastatic spread is staged, accordingly, as M0 (no metastases), M1a (metastases to lung) or M1b (any other distant site). Once histology is available, tumours can be staged I–IV

Answer 63

**Paraosteal** Osteosarcoma is the second most common primary malignancy of bone after multiple myeloma, accounting for 15% of all primary bone tumours. It usually affects those aged 10–30. Ninety- ﬁve per cent are of the primary osseous type and, of these, paraosteal osteosarcoma has the most favourable 5-year survival rate of 80%. Other osteosarcomas of the primary osseous type include periosteal (5-year survival rate 50%) and telangiectatic (less than 20%). Multicentric refers to synchronous osteoblastic osteosarcomas at multiple sites. It occurs exclusively in children aged 5–10 and carries an extremely poor prognosis. The soft-tissue type is rare, representing only 1.2% of all soft-tissue tumours. These lesions are primary soft-tissue tumours with no attachment to bone. Death occurs within 3 years in most cases, tumour size being the major predictor of outcome

Answer 64

**Enchondroma** This lesion is most likely to be an enchondroma. This is a benign cartilaginous growth in the medullary cavity and is usually asymptomatic. It most commonly occurs in the small bones of the hands and wrist but may also occur in the proximal humerus and proximal femur. Epidermoid inclusion cysts are usually in the distal phalangeal tuft and there is often a history of trauma. A bone cyst would be unusual in the phalanges.

Answer 65

**Enchondroma** Radiographic features are typical and diagnostic. A bone infarct appears as a serpiginous area with sclerotic margins and no endosteal scalloping. Chondrosarcoma shows periosteal reaction and an associated soft tissue mass.

Answer 66

**Ollier’s disease** Ollier’s disease or multiple enchondromatosis is characterized by the presence of benign intraosseous cartilaginous tumours. The estimated prevalence of the disease is 1 in 100 000. The distribution and number of lesions are variable but are often unilateral and monomelic. Complications include pain, skeletal deformities, limb length discrepancy (including Madelung’s deformity) and the potential risk of malignant change to chondrosarcoma in 20– 50% of cases. The condition in which enchondromas are associated with haemangiomas is known as Maffucci’s syndrome. Neither is usually inherited. Trevor’s disease is an epiphyseal dysplasia, whereas Lichtenstein–Jaffe´disease is another name for ﬁbrous dysplasia. Morquio’s syndrome is one of the lysosomal storage disorders known as the mucopolysaccharidoses.

Answer 67

**Maffucci’s syndrome** This diagnosis is a combination of multiple enchondromatosis and soft tissue haemangiomas. Hand and foot involvement is common and severe. The soft tissue calcifications are phleboliths from haemangiomas. In Ollier’s disease, there is absence of haemangioma and phleboliths.

Answer 68

**Chondromyxoid fibroma** This is most seen in the second and third decades and the most common site is the long bones, most often the proximal tibia and distal femur. Non-ossifying fibroma is usually asymptomatic. The appearances of a **chondroblastoma would be similar but this would most likely be epiphyseal in location** and usually presents in a slightly younger age group.

Answer 69

**Chondroblastoma**. These are radiolucent lesions that typically occupy the epiphysis of long bones in younger people, usually before skeletal maturity. They tend to be less than 4 cm in size, with approximately threequarters having a sclerotic border and one-third a calciﬁed matrix seen on plain radiographs. Chondromyxoid ﬁbromas are rare benign tumours occurring in predominantly the second and third decades of life. They characteristically have sclerotic margins and appear lobulated or ‘bubbly’. They usually arise in the metaphysis of long bones with occasional diaphyseal extension. GCTs tend to occur in young adulthood following skeletal maturity. Patients usually present with pain. The lesion is purely lytic, typically with well-deﬁned, but non-sclerotic, margins. When present in long bones, the lesions are typically metaphyseal, extending across a fused epiphysis to a subarticular location. Periosteal reaction is atypical, but expansile remodelling, cortical penetration, and soft-tissue extension may be seen.

Answer 70

**Osteochondroma** The description is classic for an osteochondroma or osteocartilagenous exostosis. These lesions are the most common benign growths of the skeleton, are usually found incidentally and are usually asymptomatic unless complications arise. Complications include fracture, vascular compromise, bursa formation and malignant transformation into chondrosarcoma.

Answer 71

**Osteochondroma** The best diagnostic feature of osteochondroma is continuity of the bony cortex and medulla with the parent bone.

Answer 72

**Thickness of the cartilage cap** Osteochondromas are the commonest bone tumours and are considered developmental exostoses rather than true neoplasms. They represent 20–50% of benign and 10–15% of all bone tumours. They are made up of cortical and medullary bone and an overlying cartilage cap. The cortex and medulla of the osteochondroma are continuous with the underlying host bone. They are typically **orientated away from an adjacent distal joint**. Lesions are frequently solitary, but multiple lesions are seen in hereditary multiple exostoses, an autosomal dominant syndrome. Malignant transformation occurs in 1% of solitary lesions and in 3–5% of patients with hereditary multiple exostoses. After skeletal maturity, **continued lesion growth, particularly of the cartilage cap, is suggestive of malignant transformation**. Although benign lesions may reach 10 cm in size, the cartilage cap should not exceed 1.5 cm after skeletal maturation. Any bone that develops by enchondral ossiﬁcation may develop an osteochondroma, the long bones of the lower extremity being most frequently affected.

Answer 73

**New lucency** Concerning features for Osteochondroma malignant transformation include: New lucency Increased scintigraphic activity Gowth after skeletal maturation Pain after puberty Cortical destruction Cartilaginous cap > 1.5cm.

Answer 74

**Chondrosarcoma** The ﬁndings describe development of **chondrosarcoma in an area of Paget’s disease.** While osteosarcoma is more common than either malignant ﬁbrous histiocytoma or chondrosarcoma in Paget’s disease, the ‘ring-and-arc’ calciﬁcation in the vignette indicates chondroid rather than osteoid calciﬁcation. Sarcomatous transformation in Paget’s is rare, occurring in approximately 1% of cases, but should be suspected if there is new focal pain or swelling. Such lesions, even osteosarcomas, are usually lucent. Periosteal reaction is often absent due to the rapidity of bone destruction. Other complications of Paget’s disease include those related to osseous weakening (deformity and fracture), arthritis, neurological entrapment, and both benign and malignant GCT. **Chondroblastoma** may have internal chondroid calciﬁcation (60%) but is a well-deﬁned, benign, lucent lesion with a sclerotic rim occurring in the **epiphyses of children and young adults.** Bronchial carcinoid metastases are usually purely osteoblastic (i.e., sclerotic, not lucent).

Answer 75

**Location in hands and feet** Chondromas are usually < 3cm, painless and in younger patients in the peripheral skeleton

Answer 76

**Deep endosteal scalloping** Distinction of enchondroma and intramedullary chondrosarcoma in the appendicular skeleton proximal to the metacarpals/-tarsals is difﬁcult radiologically. A series of 187 patients showed that chondrosarcoma was associated with endosteal scalloping, with scalloping involving more than two-thirds of the extent of the lesion being strongly suggestive of malignancy. Other powerful discriminating factors identiﬁed as favouring chondrosarcoma were cortical destruction, soft-tissue mass, periosteal reaction, radionuclide uptake at scintigraphy and pain associated with the lesion. Chondrosarcoma also tended to be larger with a mean size of 10 cm compared with 6.7 cm for enchondroma. A ground-glass matrix with arcuate calciﬁcation is characteristic of both types of cartilaginous lesion. Multiple lesions may be seen in both malignancy and enchondromatosis (Ollier’s disease).

Answer 77

**Soft tissue myxoma** The association of ﬁbrous dysplasia and soft tissue myxoma is well established and is commonly termed Mazabraud’s syndrome. The key is identifying the relationship between the bone and soft-tissue pathology, with the osseous features of ﬁbrous dysplasia usually preceding the formation of a soft-tissue mass. The condition is non-familial and more commonly affects women, the thigh being the most common location. Typical MRI appearances are of a well- deﬁned lesion with signal intensity like water, and often a fat rind or adjacent muscle high signal on T2W images is seen. Although uncommon, there have been reported cases of malignant change into osteosarcoma

Answer 78

**Fibrous dysplasia** The most common site of monostotic fibrous dysplasia is the ribs, followed by proximal femur and craniofacial bones. Three-quarters of cases present before age 30. Other benign lesions causing a ‘hot’ on bone scan include Paget’s disease, brown tumours, aneurysmal bone cysts, osteoid osteoma and chondroblastoma. Acute fractures are not usually ‘hot’ until after the first 24–48 hours.

Answer 79

**Ground-glass medulla** A ground-glass appearance is characteristic of ﬁbrous dysplasia and is the most useful discriminating factor. Other features of ﬁbrous dysplasia of the skull that can help distinguish it from Paget’s disease are symmetry of distribution, presence of a soft-tissue mass, cyst-like changes, thickness of the cranial cortices, and involvement of the paranasal sinuses, maxilla, sphenoid, orbits, and nasal cavity.

Answer 80

**increased T1 increased T2 decreased STIR** The variable proportions of vascular and fatty soft-tissue elements inﬂuence the MRI appearance of haemangiomas. Lesions with a predominantly fatty matrix show high signal intensity on T1WI, intermediate to high signal intensity on T2WI, and loss of signal on STIR or fat suppressed T2WI. If the vascular elements predominate, the lesions appear hypointense on T1WI and extremely hyperintense on STIR and T2WI. If MRI is inconclusive, CT may be helpful in identifying the typical pattern of haemangiomatous bone replacement, such as the honeycomb, ‘soap bubble’ or ‘sunburst’ appearance.

Answer 81

**Haemangioma** Vertebral haemangiomas are visualised with fine or coarse vertical striations, commonly seen in vertebral bodies. CT shows a dotted appearance in a fatty matrix. On MRI, they present as lesions, returning high signal on T1 and T2 due to their high fat content. Metastatic lesions are Intermediate signal on T1 and high on T2. Schmorl’s node affects the end plates.

Answer 82

**Haemangioma** This is most likely to be a benign haemangioma. These are relatively common lesions seen as incidental findings on spinal imaging. High signal on T1 imaging is indicative of the presence of fat within the lesion. All the other conditions would give a low-signal lesion on T1 imaging.

Answer 83

**Haemangioma** Metastatic disease, myeloma and lymphoma are the most common malignant spinal tumours, and haemangioma is the most common benign tumour of the spine. The appearances described are characteristic of a vertebral haemangioma. On MRI, these lesions typically appear of mottled low-to-high signal on T1W images depending on the degree of fat present, and of very high signal on T2W images. Other primary osseous lesions of the spine are more unusual but may exhibit characteristic imaging features that can help develop a differential diagnosis. Radiological evaluation of a patient who presents with osseous vertebral lesions often includes radiography, CT and MRI. The complex anatomy of the vertebrae means that CT is more useful than conventional radiography for evaluating lesion location and assessing bone destruction. The diagnosis of spinal tumours is based on patient age, topographic features of the tumour and lesion pattern as seen on imaging.

Answer 84

**Giant cell tumour (GCT)**. This is the classical description and location of a GCT. They occur age 20–40 years, in the long bones and occasionally the sacrum and pelvis. They are lucent, eccentric, and expansile but do not usually produce sclerosis and produce a periosteal reaction in less than a third of patients. They may have a multiloculated appearance. They originate in the metaphysis but extend to the subchondral surface in the skeletally mature. MRI often reveals ﬂuid–ﬂuid levels and some low signal on T2WI due to haemosiderin or collagen deposition. **The major differential diagnosis is an aneurysmal bone cyst (ABC), but this classically has a sclerotic margin** and usually occurs under 30 years of age (75% occur before the age of 20 years). Fibrous dysplasia would usually present at a younger age in the metaphysis with extension into the diaphysis; a trabeculated/ground-glass appearance is typical with a thick sclerotic margin and endosteal scalloping. Metastasis would be relatively rare at this age and there is no mention of a primary tumour. Osteosarcoma would have a more aggressive appearance with a wide zone of transition, periosteal reaction, cortical destruction, and soft tissue extension.

Answer 85

**GCT of the tendon sheath**. A GCT of the tendon sheath is a nodular form of PVNS. These tumours are intimately associated with a tendon sheath and are most located in the hand. They usually manifest as a small slow-growing mass, with or without pain. Radiographs may show no abnormality or non-aggressive remodelling of the adjacent bone. In MRI, these lesions are typically hypo- or isointense to muscle on T1WI and T2WI, owing to abundant collagen and haemosiderin, often with enhancement. This is like the ﬁndings of diffuse intra-articular PVNS, when the extent of haemosiderin deposition may cause hypointense nodules on T2WI and blooming artifact on gradient echo (GE) sequences. It must be stated that the degree of haemosiderin content may not always be enough to cause marked hypo-intensity on T2WI in GCT of the tendon sheath. A ganglion cyst could occur in this location and be related to a tendon sheath, but on MRI it is typically hyperintense on T2WI secondary to its ﬂuid component. There may be thin rim enhancement of the wall post administration of gadolinium. Peripheral nerve sheath tumours are typically hyperintense on T2WI with variable contrast enhancement. Lipomas are similar in signal characteristic to subcutaneous fat on MRI, i.e. hyperintense on both T1WI and T2WI. A soft-tissue haemangioma may contain phleboliths on plain radiographic imaging. On MRI, haemangiomas may be well circumscribed or have poorly deﬁned margins, with varying amounts of increased T1WI signal owing to either reactive fat overgrowth or haemorrhage. Areas of slow ﬂow are typically hyperintense on T2WI, while rapid ﬂow can demonstrate a signal void on images obtained with a non-ﬂow-sensitive sequence.

Answer 86

**Giant cell tumour** Most giant cell tumours occur in patients with closed epiphyses, and although they may originate in the metaphysis, lesions typically involve the epiphysis and abut the subarticular surface. They are classically eccentrically located lesions with a narrow zone of transition, no sclerosis, and no internal matrix mineralization. Giant cell tumours tend to be locally aggressive, with a high recurrence rate after initial treatment. Enchondromas are the commonest benign cystic lesion of the phalanges, though they are also seen in the long bones. However, those in the long bones almost always contain calciﬁed chondroid matrix. Aneurysmal bone cysts are often seen as an eccentric lytic expansile lesion, but patients are nearly all under the age of 30. Monostotic ﬁbrous dysplasia is more commonly seen in the proximal femur than distally, and lesions tend to have a sclerotic margin. Fibrous cortical defects are asymptomatic lesions seen in children, which usually regress spontaneously, so they are only rarely seen after the age of 30. They typically appear as lytic lesions with a thin sclerotic border in the metaphysis of a long bone.

Answer 87

**Extrinsic erosion is the most common osseous abnormality** Manifests as a soft tissue mass in 50-70% of cases, with normal radiographs in 20% and osseous abnormalities in 5-25%. The most common osseous abnormality are extrinsic erosions which are more often present in the ankle and foot.

Answer 88

**Distal femur** 50-65% occur around the knee but are rare in the patella

Answer 89

**Giant cell tumour** Typical features on radiograph are a lytic, eccentric, expansile, subarticular lesion with ‘soap bubble’ appearance (fluid–fluid level on MRI). Benign fibrous histiocytoma and telangiectatic osteosarcoma can also show fluidfluid levels but are metaphyseal lesions not extending to the subarticular surface. A simple bone cyst is unilocular and situated away from the articular surface.

Answer 90

**Ewing’s sarcoma with fracture** For a simple fracture with haematoma, this case has presented too early for a periosteal reaction. Neuroblastoma metastasis could be considered in a child less than 5 years old, and lymphoma should be considered in patients over 30 years age. Osteomyelitis could have been possible if there had been a previous history of localised pain, fever etc.

Answer 91

**Ewing’s sarcoma** Other causes include syphilis and infantile cortical hyperostosis.

Answer 92

**Eosinophilic granuloma** Eosinophilic granuloma is a cause of a mixed sclerotic/lytic lesion with a button sequestrum

Answer 93

A Greatest FDG uptake occurs in **primary bone lymphoma and Ewing’s sarcoma**. Osteosarcoma demonstrates moderate uptake. Most benign bone lesions are non-FDG avid, except for high giant cell containing tumours (Giant Cell Tumors (GCT), osteoblastomas, aneurysmal bone cysts) and fibrous lesions (fibrous dysplasia)

Answer 94

**Unicameral (simple) bone cyst** The fallen fragment is virtually pathognomonic for a simple bone cyst. It represents a fragment from a pathological fracture through the lesion, which has fallen to lie in a dependent location in the cyst matrix

Answer 95

**Unicameral bone cys**t This is usually asymptomatic unless fractured. The lesion usually is 2–3 cm in size, usually in the metaphysis, with its long axis parallel to the long axis of the bone. There may be endosteal scalloping of the bone and a ‘fallen-fragment sign’ (if fractured, centrally dislodged fracture fragment falls into a dependent position in the cyst).

Answer 96

**Aneurysmal bone cyst**. ABC accounts for approximately 5% of primary rib lesions, excluding myeloma. The radiological ﬁndings and age described in the question are classical for this lesion. Approximately 75% of patients are <20 years of age. The key ﬁndings on MRI are the ﬂuid– ﬂuid levels due to the settling of degraded blood products within the cysts. Fluid–ﬂuid levels may also be a feature of other lesions, including GCT and chondroblastoma, but the thin, well- deﬁned margins of an ABC should help to distinguish it from other lesions, particularly at this young age group. Fibrous dysplasia is the most common benign rib lesion. The radiographic appearances are variable but may show unilateral fusiform enlargement and deformity with cortical thickening and increased trabeculation of one or more ribs. The matrix may appear lytic, may demonstrate a ground-glass appearance, or rarely be sclerotic. Amorphous or irregular calciﬁcations may be seen within the lesion on CT, and MRI shows low to intermediate signal on T1WI and variable T2WI signal. Enchondromas more typically arise in the anterior cartilaginous portion of the rib. Radiographs reveal a lobulated, well-demarcated osteolytic lesion that demonstrates mild expansion and well-deﬁned, sclerotic margins. There is typically matrix calciﬁcation and CT is more sensitive at detecting this when the calciﬁcation is subtle. MRI shows T2WI hyperintense foci that appear to coalesce with one another and reﬂect the high ﬂuid content of hyaline cartilage. Chondroblastoma of a rib is reported in the literature but would be exceedingly rare and typically occurs in the epiphyses of long bones. Cystic haemangiomatosis is a rare disease of disseminated multifocal haemangiomatous or lymphangiomatous lesions in the skeleton and is usually an incidental asymptomatic ﬁnding.

Answer 97

**Aneurysmal bone cyst** Aneurysmal bone cyst is most common in females and 75% occur under 20 years of age. The classic presentation is of pain of relatively acute onset with a rapid increase in severity over 6– 12 weeks. Common locations include the spine, with a slight preponderance for the posterior elements, and the metaphysis of long bones – femur, tibia, humerus, and fibula. The lesion is usually expansile with thin internal trabeculations giving it the characteristic soap-bubble appearance.

Answer 98

**Intraosseous lipoma**. This is usually asymptomatic and discovered as an incidental ﬁnding in adults between 30 and 60 years. The calcaneus is the most common site for intraosseous lipoma, accounting for approximately 32% of cases. The key radiographic features are as described. The central dystrophic calciﬁcation seen in approximately 62% of cases is considered pathognomic. The major differential diagnosis of this lesion is a simple bone cyst, although this would not contain central calciﬁcation. Unlike bone cysts elsewhere, it is seen at this site into adulthood. Also within the differential diagnosis is a pseudo lesion within the calcaneus, caused by a relative paucity of trabecular bone at the same location. Again, central calciﬁcation would not be a feature in this phenomenon. Enchondroma is typically a well-deﬁned osteolytic lesion with central calciﬁcation, but it usually has a predilection for tubular bones and would be exceedingly rare in the calcaneus. The described appearances are not typical for bone infarct.

Answer 99

**Intra-osseous lipoma** The calcaneum is a common location for an intra-osseous lipoma. They do, however, also occur in the extremities, skull and mandible. There is no periosteal reaction unless there is an associated fracture. Imaging features would be like those of a unicameral bone cyst. They are often asymptomatic but can present with localised bone pain.

Answer 100

**Intraosseous lipoma** This is an expansile, non-aggressive lesion usually seen in metaphyses. It may contain a focal area of dystrophic calcification within (secondary to fat necrosis). On MRI, the lesion returns fat signal on all sequences (high signal on T1 and T2, and low signal on STIR).

Answer 101

**Chordoma.** Plain ﬁlm is very insensitive for detecting sacral lesions. Metastatic disease is much more common in the sacrum than primary malignancy. Chordoma is the most common primary sacral lesion. It is derived from the embryonic remnants of the notochord and is thus almost always found in the midline or a paramedian location with respect to the spine. It is **most found in the sacrum (50%), clivus (35%), and vertebrae (15%).** A chordoma manifests as a destructive, lytic lesion, commonly with internal calciﬁcations, at both plain radiography and CT. A large presacral soft-tissue component is usually present, as are soft-tissue components within the sacrum and sacral canal. Symptoms can include pain, sciatica, and rectal bleeding as well as other bowel and bladder symptoms, reﬂecting compromise of sacral nerves. The tumours can extend across the adjacent disc space and sacroiliac joint. On MRI, chordomas demonstrate low to intermediate signal intensity on T1WI and prominent **increased signal intensity on T2WI**. Enhancement of the soft-tissue components is variable, yet often moderate, on both CT and MR images. Chordomas demonstrate a prominent vascular stain at angiography. They are locally aggressive and develop in locations that do not permit easy surgical cure. There is an almost 100% recurrence rate; tumour seeding along biopsy tracts and surgical incisions can lead to multicentric local recurrences. Metastasis occurs in 5–43% to liver, lung, regional lymph nodes, peritoneum, skin, and heart. The 5-year survival rate is 66% for adults. Osteomyelitis in the sacrum is most often due to contiguous spread from a suppurative focus and we are told this patient was previously well. Ewing sarcoma would occur at a younger age (peaking at 15 years, 90% manifest between the ages of 5 and 30). In the case of myeloma it would be atypical for the rest of the spine to be uninvolved. The sacrococcygeal region is the most common location of teratomas discovered in infancy. It is only rarely discovered in adulthood. Teratomas are composed of a mixture of cystic and solid components. The other lesions to be included in the differential diagnosis of such a sacral mass are metastasis, sarcomas, GCT, chondrosarcoma, and ependymoma.

Answer 102

**Chordoma** Chordomas arise from notochordal rests and therefore almost always occur in the midline. They are the most common primary malignant sacral tumour and account for 2–4% of all malignant tumours of bone. They are found at all ages but most commonly occur in the fourth to seventh decades of life. Approximately half develop in the sacrococcygeal region. There is usually a large soft-tissue component, and the tumour may extend across the intervertebral disc space or sacroiliac joint. Overall, the most common sacral lesion is metastasis due to the high red marrow content, but other primary malignant lesions include myeloma, Ewing’s sarcoma and lymphoma. The most found benign tumours are giant cell tumours and aneurysmal bone cysts. Despite being relatively common in the rest of the spine, haemangiomas and osteoid osteomas are rare.

Answer 103

**Areas of low attenuation within a mass on CT** Chordoma usually appears as a low attenuation mass on CT

Answer 104

**Chordoma** This is the most common primary malignant tumour of the sacrum. Giant cell tumours are the second most common cause and are indistinguishable from chordomas on MRI.

Answer 105

**Spheno-occipital chordoma** The most likely cause is a spheno-occipital chordoma. This is associated with bony destruction in 90% of cases and is most usually within the clivus. Other sites include the sella, petrous temporal bone, floor of middle cranial fossa and jugular fossa. Sacrococcygeal chordoma is the most common subtype of chordoma and is usually located with the fourth or fifth sacral segments. Vertebral/spinal chordoma accounts for only 15–20% of all chordomas and is most often situated in the cervical spine.

Answer 106

**Thyroid** **Renal cell carcinoma** also causes expansile lytic metastases

Answer 107

**Renal** The common cancers that typically metastasize to bone are breast, lung, thyroid, renal and prostate. Due to the high prevalence of colon cancer, even though only a relatively small proportion metastasizes to bone, it forms a signiﬁcant proportion of bone metastases. Prostatic metastases are typically sclerotic, whereas breast deposits are mixed. Colonic bone metastases are usually lytic, with renal metastases typically lytic and expansile due to their highly vascular nature. Other less frequent sources of lytic expansile metastases include thyroid, melanoma and phaeochromocytoma.

Answer 108

**High signal within the disc on T2WI.** Degenerative disc disease with associated degenerative modic type 1 endplate change (endplate oedema) can mimic discitis. All the mentioned changes are seen in both conditions except high signal within the disc on T2WI, which is seen in infection/discitis. In contrast, the **degenerated disc is of low signal due to loss of hydration.** In addition, disc enhancement and paravertebral inﬂammatory tissue, soft-tissue mass, and ﬂuid collection are associated with infection.

Answer 109

**Staphylococcus aureus** The most common cause of infective discitis is Staphylococcus aureus, which gives the above typical findings. The only other relatively common cause is Mycobacterium tuberculosis, which typically spares the disc until late and usually has a large amount of associated pus.

Answer 110

**C.** Other features of tuberculosis include slow progression, marked collapse and a large paravertebral abscess, with or without calcification.

Answer 111

**Calcification within a psoas abscess is highly likely to represent TB** 50% of skeletal TB involves the spine, with the lower thoracic and upper lumbar regions being most affected. It usually begins at the anterior vertebral body. A psoas abscess may cause lateral bowing of the psoas shadow on plain film.

Answer 112

**Mycobacterium tuberculosis** The musculoskeletal system is affected in only 1–3% of tuberculous infections, but the spine is the most common skeletal location affected, accounting for 50% of musculoskeletal tuberculosis. Tuberculous spondylitis (or Pott’s disease) can result in signiﬁcant neurological sequelae. A history of pulmonary infection may or may not be present. The infection usually begins in the anterior vertebral body via haematogenous spread. The intervertebral discs are frequently involved, and the loose internal structure of the disc allows the infection to disseminate more widely, often resulting in paraspinal or psoas abscess. **Calciﬁcation within the abscess is very speciﬁc for tuberculosis.** The disease process often leads to **vertebral collapse with gibbous deformity** and obliteration of the disc space. However, elevation of the anterior ligaments by subligamentous abscess allows tracking superiorly and inferiorly, and classically spares the disc. Tuberculosis characteristically results in little reactive sclerosis or periosteal reaction, which helps to distinguish it from pyogenic infections.

Answer 113

**Intermediate signal posterior to the vertebral body on T1W images** Intermediate signal in the extradural space on T1W images is the most common appearance of extradural abscess formation. The most common primary focus of infection is discitis, but abscess formation may also be spontaneous. Patients particularly at risk are those with a history of diabetes mellitus, intravenous drug use, trauma, haemodialysis, or recent surgery (particularly dental). MRI features of extradural abscess include iso- or slight hyperintensity on T1W images when compared with the spinal cord. High signal on T2W and proton density sequences makes it difﬁcult to differentiate abscess from CSF, but these sequences are useful, as osteomyelitis and paravertebral abscess are well visualized as high-signal lesions. Administration of intravenous gadolinium contrast characteristically demonstrates diffuse enhancement of the solid component of the abscess.

Answer 114

**Clostridium infection** Gas in the soft tissues after compound fractures is a manifestation of infection. Gas gangrene after Clostridium infection is a classic example and causes extensive oedema, necrosis of tissues with gas production resulting in a severe toxic state. Other gas-forming organisms include anaerobic bacteria, coliforms and Bacteroides.

Answer 115

**Myeloﬁbrosis** This is associated with collagen proliferation in the marrow, which may be primary or secondary/ reactive following other myeloproliferative disorders. The highly structured collagen matrix has tightly bound protons that do not resonate or produce signiﬁcant signal. As a result, the marrow is of diffuse low signal intensity on all sequences. There is also no architectural distortion. In contrast, myeloma, metastases, and lymphoma are generally associated with focal or multifocal signal abnormalities. Sickle-cell anaemia causes bone sclerosis secondary to bone infarcts, which have an irregular appearance. In myeloﬁbrosis, splenomegaly is secondary to extramedullary hematopoiesis. The presence of splenomegaly is helpful in limiting the differential diagnoses. Sickle-cell anaemia is associated with a small, sometimes calciﬁed, spleen due to auto-infarction.

Answer 116

**Fast SE T2WI**. The parallel rim of hypo- and hyperintensity seen on T2WI refers to the ‘double line’ sign, which is almost pathognomic of osteonecrosis. It is most associated with avascular necrosis of the femoral head but can be seen in osteonecrosis at other sites on MRI. The ‘double line’ sign constitutes a hyperintense inner border (inﬂammatory response of bone with granulation tissue), with a hypointense periphery (reactive bone interface). The characteristic plain radiographic pattern of meta-diaphyseal osteonecrosis is that of a serpentine ring-like band of sclerosis that separates a central necrotic zone of variable lucency from surrounding normal marrow, although this pattern is a relatively late manifestation of osteonecrosis. Earlier in the course of the disease, osteonecrosis may result in a poorly deﬁned region of lucency within the medullary space, a feature that may be indistinguishable from a lytic neoplastic process on x-ray. MRI is then very useful in these cases by showing the serpentine low signal rim of the lesion on T1WI. On T2WI, the rim of the lesion may have low signal, high signal, or both (the ‘double line’ sign), the latter being the most speciﬁc sign for osteonecrosis.

Answer 117

**Mastocytosis**. This is a rare disorder characterized by proliferation of mast cells in the skin, bone marrow, liver, spleen, lymph nodes, and small bowel. Histamine released from mast cells is responsible for the associated symptoms of episodic ﬂushing, pruritis, hypotension, and diarrhoea. The serum tryptase level is also elevated in mastocytosis. Whilst the other conditions mentioned could also cause diffuse thickening of small bowel folds, the associated clinical laboratory ﬁndings and osteosclerosis are diagnostic of mastocytosis.

Answer 118

**75% of patients will have positive radiographic ﬁndings on plain ﬁlm** The clinical vignette alludes to a diagnosis of multiple myeloma (MM) and 50% bone destruction must occur before a myelomatous lesion will be visible on plain ﬁlm. Four distinct forms of bony involvement have been described in MM: (1) plasmacytoma, a solitary lytic lesion that predominately affects the spine, pelvis, skull, ribs, sternum, and proximal appendages, (2) diffuse skeletal involvement (myelomatosis), which classically manifests as osteolytic lesions with discrete margins and uniform size, (3) diffuse skeletal osteopenia, without well-deﬁned lytic lesions, which predominately involves the spine (multiple compression fractures may be seen with this pattern), (4) sclerosing myeloma, which results in sclerotic bony lesions, and is associated with POEMS syndrome (polyneuropathy, organomegally, endocrinopathy, monoclonal gammopathy and skin changes). As well as typically producing general hyperintensity on T2WI and hypointensity on T1WI in diffuse myelomatous involvement, plasmacytomas may produce focal areas of hypointensity on T1WI/hyperintensity on T2WI. STIR imaging allows better assessment of marrow involvement; fat-suppressed post contrast studies can demonstrate enhancement in focal or diffuse disease. These ﬁndings are not speciﬁc for MM and may be seen in spinal metastases. However, MM is suspected whenever MR images depict an expansile focal mass, multiple focal masses in the axial skeleton, diffuse marrow involvement, particularly at known sites of normal hematopoiesis, or multiple compression fractures in a patient with no known primary malignancy. 99m Tc-based bone scanning under-appreciates the extent of disease. FDG-PET has been used to study relapsing patients in whom recurrent disease is not easily detectable with routine imaging. PET, in this instance, has been found to aid in the detection of unsuspected sites of medullary and extramedullary disease.

Answer 119

**Joint space narrowing**. Around 5–10% of patients with sarcoidosis demonstrate skeletal involvement. The phalanges in the hands and feet are most affected. Joint space narrowing is unusual in sarcoidosis, unless neuropathic changes develop. **Typical radiographic changes include:** Cyst-like radiolucencies ‘Lace-like’ pattern of bone destruction Bone erosions Subcutaneous soft-tissue mass.

Answer 120

**Insufﬁciency fractures**. This patient has developed osteoporosis due to heparin administration (and with age). This has resulted in thoracic kyphosis and the ‘H’ sign of increased uptake within the sacral body and alae, which is classical of insufﬁciency fractures of the sacrum. Often there will have been relatively minor trauma that will not be reported by the patient, and there may be associated pubic rami fractures. Radiotherapy to the area (e.g., in gynaecological malignancy) is another predisposing factor. Multiple myeloma, metastases from renal cell carcinoma, and chordoma are typically osteolytic and result in osteopenia at isotope bone scan (IBS), although the investigation has poor sensitivity for myeloma. Brown tumours do cause increased uptake on IBS, but we are not given a history of renal failure or hyperparathyroidism to explain their presence. There is no history given to suggest infection. Bone metastases which cause an increased uptake on IBS are breast, prostate, lymphoma, pulmonary carcinoid, mucinous GI, and bladder tumours. Renal cell carcinoma, thyroid, and melanoma typically cause photopoenia.

Answer 121

**Insufficiency fracture**s Presence of bilateral sacral ala fractures with pubic fractures in this clinical context is virtually diagnostic of insufficiency fractures. Presence of marginal sclerosis at the fractures suggests chronic changes

Answer 122

**Increased conspicuity on prolonged TE images**. Distinguishing recurrent metastases from rebound hematopoietic marrow is difﬁcult on standard T1WI and T2WI sequences because both have intermediate signal intensity on T1WI and high signal intensity on T2WI. They may also occur in same anatomic regions. Out-of-phase GE imaging is useful in differentiating the two. Most neoplastic processes replace the marrow elements such as fat, osseous trabeculae, and hematopoietic elements, but hyperplastic red marrow does not. Out-of-phase imaging allows detection of intralesional fat by demonstrating a drop in signal intensity compared to in-phase images. Lengthening of echo results in loss of signal of rebound red marrow due to T2* dephasing, while the water-laden metastatic foci become more conspicuous.

Answer 123

**Polymyositis and erosive arthropathy**. There is a lot of overlap in the features of connective tissue diseases, with several patients labelled as mixed-connective tissue disease due to this. There are features of these conditions that can help differentiate them. SLE is a great mimic and can manifest in a myriad of ways. Erosive disease is not typically seen in SLE, but SLE does classically give a reducible deforming arthropathy of the hands, which is most pronounced on Norgaard views, but can appear completely normal on PA hand views. Avascular necrosis (AVN) and deforming arthropathy are not typically seen in systemic sclerosis. Acro-osteolysis and soft tissue calciﬁcations, especially in the ﬁngertip pulps, are classical features of this disease. Polymyositis classically gives high T2WI signal in muscles due to myositis. It does not typically give erosions.

Answer 124

**Renal osteodystrophy**. The ﬁrst important observation to note is the referral route. A patient from the dialysis unit is going to have renal failure, thereby excluding tertiary hyperparathyroidism and making primary less likely. This leaves Paget’s disease, osteomalacia, and renal osteodystrophy. The patient clearly has features of both hyperparathyroidism (subperiosteal resorption, brown tumour in iliac bone) and osteomalacia (Looser’s zones), giving the diagnosis of renal osteodystrophy, which has features of both. Another feature of renal osteodystrophy is the soft tissue calciﬁcation noted in the hand. The Looser’s zones are small stress fractures on the load- bearing aspect of a bone, caused by osteomalacia. This contrasts with the stress fractures seen on the tensile aspect of bones (i.e., lateral aspect of femur) seen in Paget’s disease and ﬁbrous dysplasia. Whilst Brown tumours are more closely associated with primary hyperparathyroidism, the majority occur in secondary hyperparathyroidism as this disease is much more prevalent.

Answer 125

**Metaphyseal lamellar periosteal reaction**. Hypertrophic pulmonary osteoarthropathy is a paraneoplastic syndrome secondary to the release of vasodilators. It typically causes burning pain and swelling, with the ankles and wrists being most affected. Pulmonary causes include bronchogenic carcinoma, mesothelioma, and pleural ﬁbroma. Radiographs demonstrate cortical thickening and lamellar periosteal proliferation in a dia-metaphyseal location. Bone scintigraphy will demonstrate patchy linear increased uptake along the cortical margins

Answer 126

**Hypertrophic osteoarthropathy** This is seen in multiple conditions (e.g. malignant tumours of the lung, some benign lesions, chronic chest infections). The condition manifests as cortical thickening and lamellar periosteal reaction in the diametaphyseal regions of the long bones. Bone scanning shows symmetrical uptake along the cortical margins of the diaphysis and metaphysis of tubular bones.

Answer 127

**Sickle-cell disease**. Gaucher disease and SCD can both cause H-shaped vertebrae and avascular necrosis of the humeral heads, but Gaucher disease causes splenomegaly, whereas by adulthood SCD will usually have caused splenic infarction, resulting in a small, calciﬁed spleen. Films illustrating the complications of these diseases are beloved by examiners in the 2B exam: remember to look for the mediastinal mass (extramedullary haematopoiesis) and AVN of the proximal humeri on the chest ﬁlm. Other musculoskeletal manifestations of SCD include osteomyelitis (particularly salmonella species), septic arthritis, and medullary bone infarcts. Infarction in SCD is common throughout the body and is responsible for the acute pain crisis. Infarction can occur in the liver, spleen, and kidneys, and can result in stroke. Scheuermann’s disease is osteochondrosis of the apophyses of the thoracic vertebrae and results in end-plate irregularity, Schmorl’s nodes, loss of disc space, and kyphosis. True H- shaped vertebrae are not a feature. Hereditary spherocytosis is an autosomal dominant condition. It produces splenomegaly and, as with other haematological conditions, can result in widening of the diploic spaces of the skull.

Answer 128

**Parathyroid adenoma** Parathyroid adenoma would be the most likely cause of primary hyperparathyroidism. Parathyroid carcinoma would produce a similar radiographic picture but is much less common. Brown tumours are seen in both primary and secondary hyperparathyroidism and are most common in the mandible, ribs, and pelvis; they have a variable appearance on MRI and may simulate primary or secondary neoplasms.

Answer 129

**Posterior vertebral scalloping** Posterior vertebral scalloping is not a feature. The remainder are all classic features of sickle cell anaemia, along with ‘hair-on-end’ appearance of the skull due to coarse granular osteoporosis and widening of the diploe. Osteomyelitis is a feature and is due to salmonella in over 50% of cases.

Answer 130

**Bronchial carcinoid** The most likely from the above list is a bronchial carcinoid. In men the most likely cause would be prostate. All the other conditions are more likely to produce lytic metastases than sclerotic.

Answer 131

**Hypertrophic pulmonary osteoarthropathy** The most likely explanation is hypertrophic osteoarthropathy. Thyroid acropachy changes usually occur in the upper limb. Venous stasis is a cause of periostitis rather than arterial insufficiency. Trauma would be unlikely to be bilateral unless there was a specific history. Pachy-dermo-periostitis is the idiopathic form of hypertrophic osteoarthropathy, it usually presents around adolescence and is usually associated with clubbing.

Answer 132

**Paget’s disease** Incremental fractures (banana fracture) along the convex side of the bone are classically associated with Paget’s disease. These most commonly occur in the femur where they cause lateral bowing, and the tibia where they cause anterior bowing. Compression fractures of the vertebrae are also associated with Paget’s.

Answer 133

**Paget’s disease** Asymmetrical cortical sclerosis and trabecular thickening is seen in Paget’s disease. Metastatic disease of the prostate is unlike to affect only a hemipelvis and does not directly cause acetabular protrusion. Fluorosis causes generalised sclerosis of the bones in the body

Answer 134

**Paget’s disease** Paget’s disease can be monostotic or polyostotic and demonstrates intense tracer uptake on bone scan. The area of uptake usually conforms well to the area of bone that is distorted or expanded. The most common bones involved are the pelvis, spine, skull, femur, scapula, tibia, and humerus. Many patients are evaluated after finding increased serum alkaline phosphatase.

Answer 135

**D**. Hair-on-end appearance is recognised but is relatively uncommon. Increased haematopoesis is associated with thinning of the outer table and thickening of the inner table. Characteristic facies are produced by lateral displacement of the orbits.

Answer 136

**D** Other causes of superior rib notching include SLE, scleroderma, Sjögren’s syndrome, hyperparathyroidism, Marfan’s syndrome, and osteogenesis imperfecta. NF can cause superior and inferior rib notching.

Answer 137

A **Hyperparathyroidism** is a cause of widening of the pubic symphysis. Other causes of widening include pregnancy, trauma, osteitis pubis, osteolytic metastases, infection, early ankylosing spondylitis, rheumatoid arthritis.

Answer 138

**D** Acrosteolysis is a lytic destructive process involving the distal and middle phalanges with no periosteal reaction.

Answer 139

**B** CPDD never involves nucleus pulposis, unlike ochranosis

Answer 140

**D** A rugger-jersey spine is described with subligamentous resorption and lytic brown tumour

Answer 141

**D** Lytic, mixed and sclerotic phases are recognised in Paget’s, in which the lytic and mixed types show increased activity, and a variable pattern in the sclerotic type.

Answer 142

**C** Occur much more commonly in soft tissue than bone. 25% occur in pre-existing conditions such as Paget’s. They usually present with insidious onset pain and swelling, and central mineralisation and reactive changes are uncommon.

Answer 143

**E** Plasmocytomas arise from the medulla in sites of persistent red marrow, frequently producing a soft tissue mass. Other imaging features of plasmocytomas include destructive lytic lesions with well-defined margins, cortical thinning with expansion and apparent trabeculae or a soap bubble appearance.

Answer 144

**D** MR shows marrow oedema of the femoral heads, but does not usually involve the acetabulum

Answer 145

**Brown tumour** **Brown tumours and chondrocalcinosis are features of primary hyperparathyroidism.**

Answer 146

**Rickets** Rickets (vitamin D deﬁciency) results in failure of normal bone mineralization (osteomalacia) during bone growth and may have a dietary, cultural or metabolic cause. A widened growth plate in a child is due to rickets until proven otherwise. Other features include bowing deformity, metaphyseal cupping and/or fraying, poor epiphyseal mineralization, delayed closure of the fontanelles, enlargement of the costochondral junction (rachitic rosary) and craniotabes. Scurvy is a deﬁciency of vitamin C and is a primarily a disorder of collagen production, resulting in osteopenia with dense metaphyseal lines and a sclerotic rim around the epiphysis.

Answer 147

**Sclerotic epiphyseal rim** Rickets is a deﬁciency of vitamin D in a child that results in osteomalacia of the immature skeleton. Scurvy is a deﬁciency of vitamin C and is a disorder of collagen synthesis that can occur in children or adults. Pathological fractures may be seen in both conditions. Ground- glass osteoporosis is characteristic of scurvy, with other features including a sclerotic line in the metaphyseal zone of preparatory calciﬁcation (white line of Frnkel), a radiolucent zone immediately to the diaphyseal side of the white line (Trummerfeld’s zone), corner fractures (Parke’s corner sign) and a sclerotic ring around the epiphysis (Wimberger’s sign). In addition, bleeding diathesis is seen in scurvy; therefore, subperiosteal haematoma and haemarthrosis are also features

Answer 148

**Osteomalacia** Looser’s zones or Milkman’s pseudo-fractures are seen as linear lucencies in the bone due to incomplete fractures that have nonmineralized osteoid deposited within them. The underlying failure of bone to mineralize is termed ‘osteomalacia’ (which means bone softening) and is most often due to vitamin D deﬁciency. Rickets is osteomalacia in an immature skeleton. The most common conditions resulting in an osteomalacic process and inadequate bone mineralization include renal osteodystrophy and vitamin D deﬁciency due to malnutrition/malabsorption of vitamin D or phosphate.

Answer 149

**Paget’s disease** Paget’s disease is a common progressive disorder of osteoclasts and osteoblasts resulting in bone remodelling. It is usually polyostotic and asymmetrical and affects 10% of those aged over 80. Osteoporosis circumscripta is seen in the initial phase of Paget’s disease, which is characterized by an aggressive, predominantly lytic process with intense osteoclastic activity causing bone resorption. Bone marrow is replaced by ﬁbrous tissue with large vascular channels. Geographic osteoporosis is seen in the skull and long bones, where the characteristic feature is a ﬂame-shaped radiolucency beginning in a subarticular location and progressing into the diaphysis. The disease then progresses through a mixed phase to a quiescent inactive late stage where bone turnover is decreased. The skull is involved in 29–65% of cases, most commonly the anterior calvarium.

Answer 150

**Sickle cell disease** Sickle cell disease is a haemoglobinopathy that results from the presence of abnormal b-globin chains within haemoglobin, which may manifest as anaemia, infarction and superimposed infection. It is much more prevalent in those of African–Caribbean origin. Over time, the disease produces musculoskeletal abnormalities as a result of chronic anaemia, such as marrow proliferation (which produces the characteristic changes in the skull), marrow reconversion and extramedullary haematopoiesis. Other common skeletal complications include bone softening, infection or infarction.

Answer 151

**Renal osteodystrophy** The ‘rugger jersey spine’ appearance refers to sclerotic bands along the superior and inferior endplates of the thoracic and lumbar vertebral bodies. These bands represent accumulation of excess osteoid and result in a striped appearance of the vertebral bodies. Despite being poorly mineralized, the accumulated osteoid appears opaque on plain radiographs because of its increased volume compared with that of normal bone. The ‘rugger jersey spine’ is said to be almost pathognomonic for the osteosclerosis seen with the secondary hyperparathyroidism of chronic renal failure. Renal osteodystrophy is a term for the constellation of musculoskeletal abnormalities occurring with chronic renal failure. Osteoporosis and Paget’s disease are more likely to affect the whole of the vertebrae diffusely. Discitis usually causes a reduction in the intervertebral disc space on radiographs, with indistinct endplates. The mucopolysaccharidoses result in anterior vertebral body beaking rather than sclerosis.

Answer 152

**Distal femora** MRI is superior to other imaging modalities in evaluating red (haematopoietic) and yellow (fatty) bone marrow, because of its very high sensitivity for lipid, which is present in signiﬁcantly higher concentrations in yellow marrow than in red. At birth, haematopoietic marrow is present throughout the entire skeleton. A predictable sequence of conversion of red to yellow marrow begins distally in the hands and feet and migrates proximally (over a period of 20 years) until red marrow remains only in the axial skeleton and the proximal humeral and femoral metaphyses. Reversal of this process is called reconversion. Appreciation of the areas of remaining red marrow in an adult is important, because malignant marrow inﬁltration can have a similar appearance to haematopoietic marrow, with location being a major discriminator.

Answer 153

**Renal osteodystrophy** Bone within a bone’ is a term used to describe a radiographic appearance in which one bone appears to arise within another. It can be a physiological ﬁnding in a neonate or infant due to new bone formation. Pathological conditions that can cause the appearance include periosteal new bone formation, cortical splitting, subcortical osteopenia, altered bone growth, impairment of osteoclastic activity, altered bone metabolism, crystal deposition, and iatrogenic and technical radiological factors. It is not a feature of renal osteodystrophy but is seen in hypervitaminosis D and in healing rickets

Answer 154

**Multiple myeloma** Multiple myeloma is a malignant condition of plasma cells that commonly shows inﬁltration of the bone marrow, best seen on MRI. Patterns of inﬁltration can be classiﬁed as focal, diffuse or variegated. Although marrow inﬁltration returns similar signal to marrow oedema on T1W and T2W images, inﬁltration will show diffuse enhancement following administration of intravenous gadolinium. The pattern of inﬁltration also differs. Inﬁltration will be patchy and randomly distributed throughout the vertebral bone. In contrast, bone oedema occurs adjacent to its cause, being linear at the endplates in the case of degenerative disc disease, and linear with a fracture line in osteoporotic collapse, in the pedicles adjacent to spondylolysis or at the entheses in ankylosing spondylitis.

Answer 155

**Prostatic metastases** The resulting pattern following diffuse uptake of 99m Tc-labelled diphosphonates in the axial skeleton, with little or no uptake of tracer in the soft tissues or urinary tract, is frequently referred to as a super-scan. When there is little uptake in the limbs, the cause is most likely to be diffuse metastases in the axial skeleton, most commonly prostatic or breast. Uptake in metabolic bone disease is more uniform in appearance and extends into the distal appendicular skeleton. Intense calvarial uptake disproportionate to that in the remainder of the skeleton may also be seen. The most important factor is to recognize the scan as abnormal in the absence of focal lesions. The lack of renal uptake (absent kidney sign) is a useful discriminator.

Answer 156

**SI changes are due to replacement of marrow by fat** The earliest changes occur 1-6 weeks after therapy is initiated and is due to replacement of marrow by fat. Complete replacement occurs within 6-8 weeks. Due to high radiation doses used in soft tissue tumour treatment, regeneration of normal marrow is rare, but can occur in young patients. The radiation field is usually well-defined.

Answer 157

**B** Treatment induced necrosis is a more accurate predictor of tumour response than size. Tumour size can indeed increase initially due to intralesional haemorrhage. The degree of necrosis is best evaluated with gadolinium enhanced T1 fat suppressed sequences. Neoadjuvant chemotherapy increases both recurrence-free and overall survival

Answer 158

**Radiation necrosis** Ewing’s sarcoma is a relatively common malignant bone marrow tumour related to, and sharing a common chromosomal translocation with, peripheral neuroectodermal tumours. It is a very aggressive tumour that is expressed in the radiological ﬁndings of permeative osteolysis, cortical erosion, periostitis and a soft-tissue mass. It principally affects the lower half of the skeleton, with the most frequent location being meta diaphyseal in the femur, ilium, tibia, humerus, ﬁbula and ribs. Both radio- and chemotherapy are used in treatment. Sclerosis within several months of treatment usually indicates bone healing or disease recurrence/persistence. Radiation-induced osteonecrosis is mainly an effect on the osteoblasts and is dose dependent (deterministic). It may be seen within the mandible within 1 year, but in other sites the latent period is longer and can be several years.

Answer 159

**Enhancement with intravenous gadolinium** In MRI of the spine in postoperative discectomy patients with recurrent or persistent radiculopathy, a T1W sequence with intravenous gadolinium enhancement is added to distinguish between postoperative epidural ﬁbrosis (or scarring) and recurrent disc herniation. Both can have similar, low-signal appearances on unenhanced T1W and T2W images, but **ﬁbrosis will show enhancement with gadolinium whereas recurrent disc prolapse will not enhance.** Difﬁculties arise where both conditions exist concurrently, and ﬁbrosis that is not causing nerve root irritation may also enhance. The importance of distinguishing between the two is that surgical treatment is indicated for recurrent disc herniation but is of **no value in treating postoperative ﬁbrosis, also known as failed back syndrome.**

Answer 160

**Hyperenhancement of the spleen** The hypoperfusion complex is a marker of severe injury and is an important prognostic indicator related to radiological signs on CT following blunt abdominal trauma. The features are of hypovolaemia, with small arterial and collapsed venous vessels indicating reduced circulating volume. Hyperenhancement of the kidneys, adrenal glands, pancreas and bowel wall is seen, but the spleen may be small and hypodense. If injury to the vascular pedicle is not present, nonenhancement of the spleen could be secondary to severe vasoconstriction and poor perfusion.

Answer 161

**Lateral clavicle** The lateral third of the clavicle is the most common location for posttraumatic osteolysis. It is usually preceded by a severe injury to the shoulder, typically dislocation or subluxation of the acromioclavicular joint. Changes may be evident radiographically after as little as 1 month. If no bone loss was apparent on radiographs at the time of injury, the diagnosis is unequivocal. However, if no such comparison can be made, then other **Causes of lateral clavicular osteolysis:** Rheumatoid arthritis Scleroderma Hyperparathyroidism Post traumatic osteolysis Other sites affected are the pubic and ischial rami, distal portions of the radius or ulna, the carpus and femoral neck. Widespread idiopathic osteolysis is termed Gorham’s or vanishing bone disease.

Answer 162

**Isthmus** Ninety per cent of traumatic thoracic aortic injuries occur at the **aortic isthmus, just distal to the origin of the left subclavian artery**. The isthmus is the section between the origin of the left subclavian and the attachment of the **ligamentum arteriosum** and is about 1.5 cm in length in a normal adult. The mechanism is usually rapid deceleration (but it can be due to direct trauma) as in a fall from a height or a road trafﬁc collision. The isthmus is thought to be particularly vulnerable to the shearing forces that occur with deceleration compared with the descending aorta, as it is relatively mobile and can be bent over the left bronchus main stem and left pulmonary artery. A more recent theory is that this part of the aorta is particularly vulnerable to being crushed by the surrounding bony thorax (manubrium, clavicle and ﬁrst rib) at the point of maximum deformation during high-energy injury. The ascending aorta is the site for injury in only 5% of those who survive to reach hospital but is more prevalent in cadaveric studies due to the high association of fatal cardiac injuries. The mechanism here is thought to be torsional forces or a water hammer effect (a sudden increase in intrathoracic pressure).

Answer 163

**Pseudo - meningocele**. Imaging in brachial plexus injury via CT myelography and/or MRI helps to determine whether the injury is pre- or postganglionic, which has therapeutic implications. Intradural nerve root enhancement suggests functional impairment of the nerve roots, despite morphological continuity. This is not a common ﬁnding. Signal intensity changes in the spinal cord are seen in only 20% of preganglionic injuries and lack speciﬁcity. Traumatic pseudo meningocoele, although not pathognomonic, is the most valuable sign of a preganglionic lesion. T2WI signal intensity changes within the paraspinal muscles are observed in nerve root avulsion, but this is less accurate than enhancement on T1WI post contrast. Abnormal enhancement within the multiﬁdus muscle is the most accurate of all paraspinal muscle ﬁndings since it is innervated by a single nerve root. Thickening of the brachial plexus, secondary to oedema and ﬁbrosis, is seen in postganglionic injury.

Answer 164

**Wood**. Radiography is highly sensitive for foreign bodies considered radio-opaque. All glass material is radio-opaque to some degree on radiographs and does not need to contain lead. The role for ultrasound is limited to those foreign bodies that are radiolucent, such as wood and plastic. Wood appears hyperechoic with marked posterior acoustic shadowing. Ultrasound can detect wooden foreign bodies as small as 2.5 mm in length with 87% sensitivity and 97% speciﬁcity. Plastic is also radiolucent, but less echogenic than other foreign bodies on ultrasound

Answer 165

**Superior medial maxillary** Le Fort fractures involve separation of all or part of the maxilla from the skull base. For this to occur, the posterior vertical maxillary (pterygomaxillary) buttress at the junction of the posterior maxillary sinus with the pterygoid plates of the sphenoid must be disrupted. The remaining facial buttresses are inspected to determine the class of Le Fort fracture. A Le Fort I fracture involves the inferior portions of both the lateral and medial maxillary buttresses, resulting in the maxillary arch ﬂoating free from the face. In a Le Fort II fracture, the inferior lateral maxillary buttress is similarly injured, but, unlike type I, it is associated with fracture of the superior portion of the medial maxillary buttresses, resulting in dissociation of the entire maxilla from the skull base. A Le Fort III fracture results in the whole face ﬂoating free from the skull with disruption of the superior portions of both the lateral and medial maxillary buttresses and upper transverse maxillary buttress.

Answer 166

**Oral, rectal and IV contrast** Oral, rectal and IV contrast A triple contrast technique has been advocated in penetrating trauma where there may be concern regarding small bowel or colon trauma. If no oral or rectal contrast are given, then a small bowel or colon injury can easily be missed.

Answer 167

**Impaction** Fracture sites that have a poor blood supply, either as a result of the original injury or due to subsequent surgical treatment, may go on to develop atrophic non-union where the bone ends become osteoporotic, thin and pointed (osteolysis) with no evidence of fracture healing. A fracture site that is very mobile may develop hypertrophic non-union where there is attempted healing denoted by excessive callus formation, but the fracture cleft persists. Open fractures are often high energy, with soft-tissue damage and comminution of fracture fragments, and are prone to infection, all of which predispose to non-union. Osteomyelitis in any fracture can result in delayed, non- or malunion. Non-union in most skeletal locations should not be diagnosed radiographically until 6 months have passed, particularly in the presence of complicating factors.

Answer 168

**CT head** According to NICE guidance he should undergo CT head and the investigation should be performed within the hour following referral. The fact he is anticoagulated, over 65 and experienced a loss of consciousness would all be factors in warranting an urgent CT head. (Ref: National Institute for Health and Clinical Excellence

Answer 169

**Extradural haematoma** Extradural (or epidural) haematoma is the accumulation of blood in the potential space between the inner table of the skull and the dura. Ninety per cent of cases are associated with a fracture of the temporal bone which traverses and ruptures the **middle meningeal artery** (in 60–90%) or vein. In children, vascular injury may occur here without a fracture. In half of cases, there is a lucent interval between injury and the onset of deteriorating consciousness level, as opposed to diffuse axonal injury where coma is immediate. CT appearances are of an extra-axial, biconvex, high-attenuation collection. A subdural haematoma is caused by shearing forces on small bridging veins and is not necessarily associated with a fracture of the calvarium, although this may coexist. It differs from an extradural haematoma not in radiographic location but in that it has a crescentic rather than a biconvex shape

Answer 170

**Cortico-medullary petechial haematoma** Contusions are traumatic injuries to the cortical grey matter of the brain and make up approximately half of primary intra-axial traumatic lesions. They are often multiple and bilateral, with the most common locations being the inferior frontal lobes and temporal poles. Diffuse axonal injury results from rotational shearing forces on cerebral white matter and common locations are white matter-rich areas, such as the corticomedullary junction, centrum semiovale, corpus callosum and cerebellum. In comparison to diffuse axonal injury, contusions tend to be larger and more superﬁcial, with a higher proportion being haemorrhagic due to the increased vascularity of grey compared with white matter. Local or widespread oedema can be seen in both conditions.

Answer 171

**Regional sympathetic dystrophy** This is the typical appearance, history, and imaging findings for regional sympathetic dystrophy. This may occur following fractures or secondary to other pathologies such as primary or secondary bone tumours. There is **overactivity of the sympathetic nervous system causing pain, swelling and hyperaemia with excessive bone resorption.** This is usually in a periarticular distribution and may simulate other disease processes.

Answer 172

**Reflex sympathetic dystrophy** This is commonly associated with trauma. The condition causes hyperhidrosis skin changes with excessive pitting oedema, sudomotor changes (hyperhidrosis and hypertrichosis), pain and patchy osteopenia. Three-phase bone scan shows increased blood flow, increased blood pool and increased periarticular uptake on delayed images.

Answer 173

**Reflex sympathetic dystrophy** A history of trauma, periarticular uptake on bone scan and osteoporosis suggests reflex sympathetic dystrophy. All other conditions are likely to affect both feet.

Answer 174

**Pulmonary embolism** Pulmonary embolism is a common complication following immobility and major surgery, particularly orthopaedic surgery of the pelvis. **PE typically occurs 7–10 days post-surgery**. Chest radiograph ﬁndings can be normal but include small effusion, collapse or consolidation, elevation of the hemidiaphragm, a prominent pulmonary artery and hyper-trans-radiance of the affected side (Westermark sign). **Fat embolism** is preceded by long bone injury in 90% of cases but usually **occurs within 36 hours of the injury** and is much less common than pulmonary embolus from deep vein thrombosis even in the context of major trauma. Pneumonia and pneumothorax do of course occur in postoperative patients, but it would be reasonable to expect associated ﬁndings on the chest ﬁlm. Hyperventilation should be a diagnosis of exclusion once other potentially serious causes have been excluded

Answer 175

**Incudo-stapedial joint dislocation** Longitudinal fractures of the temporal bone are more common than transverse fractures and account for over 85% of temporal bone fractures. They are associated with otorrhea, conductive hearing loss, pneumocephalus, herniation of the temporal lobe and incudo-stapedial dislocation. Transverse fractures are associated with sensorineural hearing loss, and a higher percentage of facial nerve palsies.

Answer 176

**Injury is typically due to hyperextension** The scaphoid bone is the most fractured carpal bone, and the mechanism is usually a fall onto the outstretched hand – ie. hyperextension of the wrist. The reported sensitivities and specificities of CT are 89–97% and 85–100%, respectively. The high negative predictive value of CT (96.8–99%) makes it very useful for ruling out a fracture. Scaphoid fractures are missed on initial radiographs in up to 30% of cases

Answer 177

**Washout of the high-attenuation area on delayed imaging** Washout of the high-attenuation area is one of the features of a pseudoaneurysm. A pseudoaneurysm is likely to be adjacent to a vessel and whilst there will be a relatively well- defined area of high attenuation on arterial phase imaging, this will diminish in intensity on five-minute delayed imaging. In contrast to this, an area of active extravasation will often appear as a jet of high attenuation which continues to collect and enlarge on delayed phase imaging.

Answer 178

**200 ml** The approximate minimal detectable fluid volume is 200 ml. The distribution of free fluid will be determined by both anatomical and physiologic factors and therefore the sensitivity of the scan will depend upon the areas scanned. Ultrasound is often used in conjunction with multidetector CT, particularly in the management of patients who have been involved in trauma.

Answer 179

**Type II** The Salter–Harris classiﬁcation originally described ﬁve types of growth plate injury. Type I (6–8%) is slip of the epiphysis due to shearing forces, and the fracture line is a cleavage through the growth plate only. Type II is by far the most common (75% of injuries) and is also a shearing injury. The fracture line involves the physis and extends proximally into the metaphysis separating a triangular fragment. Type III (6–8%) occurs in partially closed growth plates, involves the physis and extends distally into the epiphysis, involving the articular surface. Type IV (10–12%) is a fracture that begins in the metaphysis, crosses the physis and also involves the epiphysis. Type V (1%) is a crush injury. The classiﬁcation indicates progressively poorer prognosis about future growth disturbance. There have been subsequent additions to the classiﬁcation.

Answer 180

**Central cord syndrome** In trauma, an incomplete spinal cord injury is one in which there is any degree of sparing of motor or sensory function distal to the site of injury, whereas complete cord injury results in complete lack of neurological function distal to the injury. The diagnosis can be made only in the absence of spinal shock, a transient spinal cord concussion. Central cord syndrome is the most common incomplete injury and is associated with hyperextension injury in middle-aged patients; injury to centrally located grey matter in the cord causes a greater motor neurological deﬁcit in the upper than in the lower extremities. Sensory involvement can be variable, and bowel and bladder function may be affected. Anterior cord syndrome, caused by anterior spinal vascular insufﬁciency, causes complete motor paralysis with sparing of the posterior columns. SCIWORA is seen in children, when the elastic cervical spine deforms sufﬁciently to cause cord injury but without any radiological ﬁndings. Brown-Sequard syndrome results from hemi transection and causes ipsilateral muscle paralysis and contralateral hyperaesthesia to pain and temperature

Answer 181

**First rib** First rib fracture is considered a harbinger of major trauma, with approximately two-thirds of fractures being associated with major chest injury and carrying a signiﬁcant mortality. The anatomy of the ﬁrst rib is such that it is protected from the minor insults that often break other ribs, and fracture of the ﬁrst rib usually indicates violent blunt trauma to the thorax. Associated local injuries include damage to the brachial plexus, major vascular structures and the underlying lung and heart. There is also an association with signiﬁcant abdominal injury, but the major cause of death in patients with a ﬁrst rib fracture is an associated head injury. It is rare for a ﬁrst rib fracture to be an isolated ﬁnding

Answer 182

**Contralateral condylar neck** The mandible is best considered as a closed ring, and as such approximately half of all mandibular fractures are bilateral and multiple. The majority occur at the angle, and a signiﬁcant portion occur at the condylar neck, a common pattern of injury being an ipsilateral body fracture from a direct blow, with a contralateral angle or condylar neck fracture due to transmitted rotation force compressing that side. Fractures of the condylar neck have a limiting effect on the opening and closing of the jaw and can be missed radiographically. Fractures in the midline are also subtle and account for a signiﬁcant minority. A ﬂail mandible occurs when the anterior support for the tongue is lost due to a bilateral fracture. This injury carries the risk of the tongue prolapsing posteriorly and occluding the airway.

Answer 183

**Intra-abdominal haemorrhage** A Malgaigne fracture of the pelvis is a fracture of the **pubic rami and an ipsilateral sacroiliac joint fracture** and occurs due to high-energy blunt trauma. It represents complete disruption of the pelvic ring and therefore an **unstable fracture**. In such fractures, distortion and **disruption of the pelvic soft tissues and vascular injury** involving the rich blood supply in the pelvis will not be tamponade by the bony ring, as the pelvis will expand to accommodate ever-increasing haematoma. Mortality rate from major pelvic trauma is 10%; other common causes of death include multiorgan failure and sepsis, the latter expected to take several days to evolve.

Answer 184

**Aggressive granulomatous disease**. Well-delineated, **rounded, focal areas of lucency at the cement bone interface,** which are progressive, are suggestive of either infection or aggressive granulomatous disease. It can occur with both cemented and non-cemented components. Its origin is thought to be multifactorial. Metal, cement, or polyethylene fragments may penetrate the cement bone interface and induce a focal inﬂammatory foreign-body reaction, leading to osteolysis. **Primary loosening usually manifests as a wide (>2 mm) radiolucent zone** at the cement–bone or metal–bone interface or a progressive radiolucent zone at the metal–cement interface. The radiolucent zones are **not typically rounded.** Cement fractures are thin linear lucent areas within the cement. They may be asymptomatic but are important to identify as they may lead to component failure. Metal bead shedding is deﬁned as opaque micro-fragments separated from the porous coated femoral stem. Metal beads can be seen on immediate postoperative radiographs, because of the stem insertion. Bead shedding might later occur with loose non-cemented components, reﬂecting micro-motion of the stem. These metal beads are seen in the soft tissue adjacent to the hip replacement and their increase in number on follow-up indicates loosening.

Answer 185

**Reverse hybrid total hip replacement.** A combination of a cemented acetabular cup and an uncemented femoral stem is known as a reverse hybrid hip total hip replacement. A hybrid total hip replacement is a combination of a cemented femoral stem and an uncemented acetabular cup. A unipolar hemiarthroplasty comprises a combination of a femoral component articulating directly with the native cartilage surface of the acetabulum. A bipolar hemiarthroplasty comprises a combination of a femoral component articulating with a cup inserted into the native acetabulum without ﬁxation. This cup is usually made of polyethylene with a metal backing and can normally move within the native acetabular cavity because of the absence of ﬁxation. Hip resurfacing consists of replacing the surface of the femoral head by a metallic ‘cap’ without removing the femoral neck or instrumenting the femoral diaphysis. The cap used on the femoral head is virtually the same size as the natural head and articulates with an acetabular prosthetic cup, usually made of metal. This type of procedure is favoured in younger active patients and may allow for easier revision to a total hip replacement in later years

Answer 186

**Cam-type acetabular impingement** Femoro-acetabular impingement (FAI) occurs because of repetitive microtrauma due to an anatomic conflict between the proximal femur and the acetabular rim at the extremes of motion. An osseous bump at the femoral head–neck junction is present in 50% of cam-type FAI and only 33% of pincer-type FAI. The alpha angle, drawn on the AP pelvis radiograph, is formed by a line drawn from the centre of the femoral head through the centre of the femoral neck, and a line from the centre of the femoral head to the femoral head–neck junction, found by the point by which the femoral neck diverges from a circle drawn around the femoral head. A normal patient’s alpha angle is around 45’, whereas for patients with FAI it may be around 70’.

Answer 187

**Cam femoro-acetabular impingement** Cam is the most common form of femoro-acetabular impingement in men, typically presenting in the third or fourth decade. It is often related to a previous slipped upper femoral epiphysis in the teenage years. A change in the rotational axis (increase in the alpha angle) causes the proximal superior femoral neck to impinge upon the superior acetabular margin and labrum, in turn causing intermittent pain, particularly in physically active individuals. Even without a history of slipped femoral epiphysis, an osseous bump on the superior femoral neck obliterating the femoro-acetabular sulcus can cause symptoms. Labral or articular cartilaginous tears can follow repetitive microtrauma, leading to persistent pain and locking. The pincer type is more common in women and is caused by an abnormally deep acetabulum.

Answer 188

**Loosening** Early changes (less than six months) are almost always due to infection. Up to four years, infection remains the most likely cause, but after this point loosening becomes more common. Every year, 38 000 hips are replaced in the UK. A routine postoperative film is usually performed; an excessively varus stem may lead to loosening.

Answer 189

**Heterotopic ossification** Heterotopic ossiﬁcation, also known as myositis ossiﬁcans, is a benign, self-limiting process of ossiﬁcation occurring within skeletal muscle. Seventy-ﬁve per cent of cases are due to trauma (including iatrogenic trauma), with other causes including paralysis, burns, tetanus and intramuscular haematoma. The areas of new bone are surrounded by ﬁbrotic connective tissue, which can be seen as a soft-tissue mass on MRI. Some heterotopic ossiﬁcation is seen in half of all total hip replacements, with one-third considered clinically signiﬁcant. It is classiﬁed radiographically according to the Brooker classiﬁcation.

Answer 190

**Patients with developmental dysplasia of the hip are at increased risk of labral tears** The increased risk of labral tears in developmental dysplasia is due to the increased stress placed upon the acetabular rim and labrum. A communication between the joint capsule and iliopsoas bursa has been described as a normal finding in 10–15% of patients. A dilute solution of 0.2 mmol/L gadopentetate dimeglumine solution would usually be used for arthrography. A normal labrum has uniformly low signal on T1-weighted imaging with slightly increased signal on gradient echo imaging. Appearances on T2-weighted imaging can be more variable.

Answer 191

**A focus of central low SI surrounded by a rim of high SI on contrast enhanced T1 indicates muscle infarction and necrosis** Diabetic myopathy typically presents with sudden onset pain and swelling of the affected muscles and a palpable painful mass in 1 ⁄ 3 of cases. Fever is present in 10%. Other complications of diabetes are usually present. Myopathy affects bilateral lower limbs in 18%. It usually demonstrates diffusely high SI on T2 with areas of high SI on T1 indicating haemorrhagic infarction

Answer 192

**Radiographic changes include alternating osteopenia and sclerosis** This is a self-limiting but often protracted condition secondary to repetitive microtrauma with osteoclastic activity and osseous resorption. Radiographs show irregularity of subchondral bone plate, erosions, fragmentation and alternating osteopenia and sclerosis. It may lead to joint space widening

Answer 193

**3 mm, lucent line at the cement/prosthesis interface** The artefact created by metallic prostheses on CT and MRI means that plain radiography has an important role in the evaluation of postoperative arthroplasty joints. Cemented prostheses may normally show a 1–2 mm lucent line at cement interfaces, but deﬁnite loosening is diagnosed with progressive widening of this zone. Other speciﬁc indicators of loosening in both cemented and uncemented prostheses include migration of components or a new abnormality of alignment. Periosteal reaction and sclerosis can be normal ﬁndings, particularly in uncemented prostheses. Serial imaging is often required to conﬁrm the diagnosis of loosening.

Answer 194

**Metaphyseal bone resorption** Catterall described four radiographic signs that indicate a femoral ‘head at risk’ of avascular necrosis (Perthes’ disease), to predict those cases in which considerable collapse of the femoral head may occur. 1. Gage’s sign is a radiolucent V-shape seen in the lateral side of the epiphysis on frontal pelvis radiographs. 2. Calciﬁcation lateral to the epiphysis indicates a small area of lateral head collapse. 3. The third sign is lateral subluxation, best seen as an increased inferomedial joint space, which when seen in conjunction with the ﬁrst two worsens the prognosis. 4. Finally, in some individuals the normal growth plate is more horizontally orientated, which results in normal weight-bearing forces exerting a shearing force on the growth plate, rather than a compressive force as seen in the more common transversely orientated growth plate. A horizontal growth plate is therefore considered a further poor prognostic sign in Perthes’ disease

Answer 195

**Posterior rim/wall** Acetabular fractures are common in multiple or major trauma patients, particularly those involved in road trafﬁc collisions, and are classiﬁed according to the Letournel classiﬁcation. Fractures are often complex and require accurate delineation with CT, often following limited or suboptimal initial radiographic investigation with or without oblique pelvic (Judet) views. Isolated posterior rim or wall fractures are the most common type (27%) and are associated with a high frequency of posterior dislocation of the femoral head causing sciatic nerve injury. If the entire posterior column is involved in the fracture, there is a lower incidence of sciatic nerve injury, as the femoral head may not be dislocated. Anterior injuries are uncommon (5%) and may be associated with anterior femoral head dislocation and iliac wing fracture. Transverse fractures account for 9%.

Answer 196

**Transient osteoporosis** Transient osteoporosis of the hip is part of the bone marrow oedema syndromes that also encompass migratory regional osteoporosis and transient bone marrow oedema. The condition is spontaneous and self-limiting, clinical recovery occurring in several weeks to months with no speciﬁc treatment, although radiographic changes lag behind. It is seen in pregnant women in the third trimester and middle-aged men. The radiographic hallmark is the loss of subchondral cortex in the femoral head, and marrow oedema is seen on MRI with intense uptake of 99m Tc-labelled diphosphonates on bone scintigraphy. The aetiology is uncertain, but speculation has been made that the bone marrow oedema syndromes are related to reﬂex sympathetic dystrophy. The appearance of transient osteoporosis of the hip may be mimicked by osteonecrosis.

Answer 197

**Renal osteodystrophy** Patients with renal osteodystrophy have extensive soft tissue calcifications, particularly in periarticular distribution. ‘Super scan’ appearance is also a feature.

Answer 198

**Type I Salter–Harris injury** Slipped capital femoral epiphysis is classified as a type I Salter–Harris injury because there is a slipped epiphysis due to the shearing force of an injury, separating the epiphysis from the metaphysis. There is no fracture of the metaphysis or the epiphysis itself.

Answer 199

**Charcot’s joint** The radiographic features are those of Charcot’s joint. Given the history of treated sexually transmitted disease, syphilis must be considered

Answer 200

**Bone oedema involving the medial facet of patella and lateral femoral condyle**. Transient dislocation of the patella typically occurs laterally because of a twisting injury in a ﬁxed and ﬂexed knee. The medial facet of the dislocated patella impacts against the lateral femoral condyle, resulting in the classic bone contusion pattern. Rarely oedema may also be seen in the adductor tubercle of the medial femoral condyle due to avulsion of the medial patello-femoral ligament.

Answer 201

**Transient patellar dislocation** Transient patellar dislocation always occurs laterally and was originally thought to be an injury conﬁned to teenage girls with abnormal patellofemoral anatomy but is now considered a potential injury in anyone who partakes in athletic activity. The most common ﬁnding is effusion and lateralization of the patella with or without an abnormally shallow femoral sulcus. Other ﬁndings seen on MRI are contusions of the lateral femoral condyle and medial patella with potential osteochondral defects, and disruption or sprain of the medial retinaculum. Less speciﬁc ﬁndings include loose bodies and associated ligamentous or meniscal injury.

Answer 202

**Haemophilia**. There are three salient features to this question. Firstly, widening of the intercondylar notch— this is typically caused by haemophilia and JRA, but can also be caused by tuberculous arthritis. Secondly, causes of arthritis with variable loss of joint space. This is seen in tuberculous arthritis, amyloid, and PVNS, and may be present in haemophilia, although this can also cause severe arthropathy. Thirdly, causes of blooming artefact on GE sequences. This is usually caused by haemosiderin and is found in PVNS and haemophilia. Thus, when the whole picture is considered, the diagnosis is haemophilia.

Answer 203

**Pigmented villonodular synovitis** Pigmented villonodular synovitis is a benign proliferative disorder of the synovium that has a propensity for young to middle-aged adults and typically has a long history. On plain radiographs, joint space and bone mineralization are typically preserved until late in the disease, but softtissue swelling or effusion may be apparent early on. Haemorrhage is relatively common and can result in haemarthrosis and blooming artefact seen on gradient echo MRI sequences. Malignant ﬁbrous histiocytoma is the most common soft-tissue sarcoma after age 50. Synovial osteochondromatosis is more common in men and is characterized by proliferation of the synovium with formation of cartilaginous nodules (that often calcify) but does not show haemorrhage. Baker’s cyst has synovial ﬂuid characteristics on MRI and is located posterior to the joint.

Answer 204

**Pigmented villo-nodular synovitis** The MRI appearances described are typical of pigmented villonodular synovitis, showing low signal of abnormal synovium on all sequences.

Answer 205

**Lipoma arborescens** This condition is seen most in the suprapatellar pouch, with small to large frond-like masses arising from synovium. On MRI, the masses show characteristic signal of fat on all sequences. Saturation on STIR images is diagnostic

Answer 206

**Bruising at the anterior aspect of the tibia** Such bruising occurs in a dashboard injury when a posteriorly directed force is applied to the anterior aspect of the proximal tibia with the knee in ﬂexion, such as occurs in an RTA. Bruising is also occasionally found in the posterior patella in this situation. Associated soft- tissue injuries are disruption of the posterior capsule and posterior cruciate ligament (PCL). The pattern of injury in option A is caused by the pivot shift injury (valgus load in ﬂexion combined with external rotation of the tibia or internal rotation of the femur). This will result in anterior cruciate ligament (ACL) disruption and the resultant anterior subluxation of the tibia causes impaction of the lateral femoral condyle against the posterolateral margin of the lateral tibial plateau. Soft-tissue injuries that may occur are tears of the posterior capsule, the posterior horn of the lateral or medial meniscus, and the medial collateral ligament (MCL). The kissing contusions in option C: are because of hyperextension injury; resulting injuries may be to the ACL, PCL, or menisci. Option D describes the pattern found in clip injury, which involves a pure valgus stress while the knee is in mild ﬂexion. The second area of bruising in the medial femoral condyle in this situation is due to avulsive stress to the MCL. The ﬁndings in option E are in keeping with transient lateral patellar dislocation, as discussed elsewhere in this chapter.

Answer 207

**Torn medial meniscus** Truncation of a meniscus may be due to previous injury or surgical resection, but in the absence of a relevant history it suggests meniscal tear with displacement of the body of the meniscus. On sagittal sequences, one would normally expect to see a full ‘bow-tie’-shaped meniscus on three or more contiguous images, as the meniscal body is approximately 11 mm in thickness (this of course will depend on slice thickness). Any fewer suggests a meniscal body tear with displacement of the fragment. The fragment often ﬂips into the intercondylar groove of the femur to lie anterior and parallel to the posterior cruciate ligament, giving the impression of two similar structures. This injury is known as a bucket-handle tear.

Answer 208

**Spontaneous osteonecrosis of knee** Typical subchondral fracture in elderly patient after minor knee injury.

Answer 209

**Avascular necrosis** Avascular necrosis of the femoral head is a complication after hip dislocation. It may be seen as a wedge-shaped or geographical area of **subchondral ischemic focus** in the **weight-bearing area.** On MRI, there is a hyperintense inner border parallel to a hypointense periphery.

Answer 210

**Avascular necrosis** This appearance on MRI is typical of avascular necrosis.

Answer 211

**Medial head of gastrocnemius and semimembranosis**. Identiﬁcation of anechoic cysts communicating with ﬂuid between the semimembranosis and gastrocnemius tendons conﬁrms the diagnosis of Baker’s cyst. It is important to perform further imaging if the mass in the posterior compartment lacks signs of communication with ﬂuid between the semimembranosis and medial gastrocnemius tendons. If this is the case, there are other possibilities for the lesion, including meniscal cyst or even a myxoid sarcoma.

Answer 212

**Sinding–Larsen–Johansson syndrome**. This is a traction tendonitis occurring at the attachment of the patellar tendon to the inferior pole of the patella. Repetitive stress/microtrauma at the tendinous attachment results in calciﬁcation or ossiﬁcation of the tendon on the plain ﬁlm. MRI demonstrates oedema within the tendon and at the inferior pole of the patella. Similar changes occurring at the tibial attachment of the patellar tendon is called Osgood- Schlatter disease. Patellar sleeve fracture is a unique paediatric injury in which the cartilage at the inferior pole of the patella is avulsed along with a small bone fragment. The quadriceps tendon inserts into the superior pole of the patella, therefore a partial tear produces oedema at the superior pole of the patella

Answer 213

**Synovial osteo-chondro-matosis**. The primary form of this represents an uncommon benign neoplastic process with hyaline cartilage nodules in the subsynovial tissue of a joint, tendon sheath, or bursa. Secondary synovial chondromatosis is associated with joint abnormalities, such as mechanical or arthritic conditions, that cause intraarticular chondral bodies. The primary form of the disease predominantly affects men in the third to ﬁfth decades. The knee is the most common site, but it is also seen in the hip, shoulder, elbow, and ankle; less commonly the MCP, IP, distal radioulnar, and acromioclavicular joints are involved. It can rarely involve extra-articular sites, the synovium about the tendons, or bursa. Clinical symptoms typically include pain, swelling, and restriction of the range of motion of the joint. Radiologic ﬁndings are frequently pathognomonic. Radiographs reveal multiple intraarticular calciﬁcations (70–95% of cases) of similar size and shape distributed throughout the joint, with typical ‘ring-and-arc’ chondroid mineralization. Extrinsic erosion of bone is seen in 20–50% of cases. Juxtaarticular osteopenia is not typically apparent in synovial chondromatosis unless it is the result of disuse. CT is often diagnostic if the bodies are adequately mineralized and is particularly helpful for identifying characteristic ring-and-arc or punctate mineralization and the multiplicity of nodules in cases for which radiographic ﬁndings are normal or equivocal. Lack of mineralization of the bodies does occur in which cases MRI is very helpful to distinguish from, for example, PVNS or amyloid. The most common pattern on MRI (77% of cases) reveals low to intermediate signal intensity with T1WI and very high signal intensity with T2WI with hypointense calciﬁcations.

Answer 214

**PVNS**. This is a monoarticular tumour-like proliferation of synovium that occurs in joints, bursae, and tendon sheaths. It may be focal or diffuse. It occurs most frequently in the knee (80% of cases), then the hip, ankle, shoulder, and elbow. The abnormal synovium is prone to haemorrhage, thus producing blooming artefact on GE sequences, secondary to haemosiderin deposition. In general the classic MRI appearance is variable low signal intensity on all sequences (T2WI signal being more variable due to fat, oedema, and blood products). Early changes involve a focal mass and joint effusion. Subsequently large erosions, synovial hypertrophy, and subchondral cysts may occur. Joint space is preserved until advanced disease is present and bone density is normal. After IV contrast at CT, PVNS shows variable enhancement, which can be striking. The differential diagnosis includes diseases causing recurrent haemarthroses, e.g. haemophilia and haemochromatosis (PVNS is monoarticular) as well as gout, amyloid, synovial chondromatosis, and tuberculosis. Some 90% of synovial cell sarcomas do not originate from a joint. They are usually isointense to muscle on T1WI, with heterogeneous high-signal intensity on T2WI. Regional migratory osteoporosis would obviously involve loss of bone mineralization, as well as marrow oedema. Gout demonstrates typically ‘rat’s bite’ para-articular erosions and soft-tissue calciﬁcation; when it involves the knee it tends to affect the patello-femoral compartment.

Answer 215

Although all are causes of a widened intercondylar notch, the radiographic features are of haemophilic arthropathy. MRI shows low SI of hypertrophied synovial membrane on all pulse sequences due to haemosiderin

Answer 216

**Posterior cruciate ligament**. The avulsion injury described is a **reverse Segond fracture.** This injury is known to be associated with both mid-substance tears of the **posterior cruciate ligament** and avulsions of the PCL from the posterior tibial plateau. They can also be associated with medial meniscus injuries. They are not to be confused with a **Segond fracture**, which is a small elliptical fragment of bone avulsed from the **lateral tibial plateau** at the lateral joint margin, best seen on the AP view of the knee. They have a strong association with tears of the **anterior cruciate ligament** and meniscal tears.

Answer 217

**Complete anterior cruciate ligament rupture** The avulsion fracture described is a Segond fracture, which is classically associated with anterior cruciate ligament (ACL) rupture and represents avulsion of the meniscotibial portion of the middle third of the lateral capsular ligament. Anterior translocation of the tibia occurs in complete ACL rupture, and manifests clinically as the anterior draw sign. Also associated with ACL rupture is an impaction injury of the lateral femoral condyle, which can be seen on radiographs as a deepened lateral femoral condylar sulcus, although sometimes this cannot be identiﬁed on acute ﬁlms.

Answer 218

**Anterior cruciate ligament** The fracture described is a Segond fracture, originally documented by Dr Paul Segond in 1879 after a series of cadaveric experiments. The Segond fracture occurs most commonly in association with anterior cruciate ligament injuries (75–100%) and medial meniscal injuries. Due to the high rate of associated injuries, a patient who sustains a Segond fracture will require further imaging, usually by way of MRI, to specifically investigate the ligaments and menisci.

Answer 219

**Myositis ossificans** Often there is no distinct history of trauma, although this is the most common cause. It usually occurs in the large muscles of the extremities and in the early stages it can be difficult to distinguish from soft-tissue sarcomas. It is, however, separate from bone, unlike parosteal sarcoma and post-traumatic periostitis. This is a self-limiting condition, most commonly occurring in young athletic adults, with resorption occurring in approximately one year.

Answer 220

**Pattern of ossiﬁcation in the lesion**. The pattern of ossiﬁcation is likely to be the most helpful. In **post-traumatic myositis ossiﬁcans,** the ossiﬁcation occurs classically ﬁrst at the **periphery**. whereas in **par-osteal osteosarcoma**, the ossiﬁcation is **diffuse, but predominantly central.** Periosteal reaction is typically absent in both these lesions and both lesions may contain lucent areas on plain radiograph. A lucent cleft between the mass and the bony cortex, representing periosteum, is characteristic in par-osteal osteosarcoma, but frequently is not seen as the tumour envelops bone. A thick lucent zone separating myositis ossiﬁcans from an adjacent bony cortex is typical but may not be seen on plain radiograph if the lesion is immediately juxta cortical.

Answer 221

**Malignant fibrous histiocytoma** Soft-tissue malignant fibrous histiocytoma is the most common primary malignant soft tissue tumour of later adulthood. It is most seen in the lower extremities. It has a metastatic rate of 42% and most commonly metastasises to the lung. Osseous malignant fibrous histiocytoma presents as a painful, tender, rapidly enlarging mass and most commonly arises in the metaphysis of long bones.

Answer 222

**Meniscal cys**t Meniscal cysts are very commonly associated with meniscal tears. MRI shows classic features of the cyst, related to the parameniscal structures. Lateral meniscal cysts tend to be smaller but are often more symptomatic than cysts in the medial counterparts.

Answer 223

**High signal around the MCL on T2* on coronal imaging** The only abnormal finding is the presence of high signal around the MCL on T2* imaging. This would represent oedema or haemorrhage around the MCL and may be associated with a tear. Bowing of the PCL occurs when the knee is extended. A medial patellar plica is a normal finding in approximately 50% of the population. This is an embryological remnant from when the knee was divided into three compartments

Answer 224

**C**. The normal infrapatellar tendon is homogenously low SI on all sequences. A triangular area of high signal at the patellar enthesis when imaged on gradient echo is of no clinical significance. The paratenon is more commonly the primary site of acute inflammation in the Achilles tendon than the infrapatellar tendon. An echo-poor halo around the tendon is seen in paratenonitis on US.

Answer 225

**C** Grade 1: focal hypointense areas not extending to cartilage surface Grade 2: focal hypointense areas extending to the cartilage surface with preservation of sharp cartilage margins Grade 3: loss of sharp dark margin between articular cartilage of the patella and trochlea and focal hypointense areas extending to the articular surface but not down to the osseous surface.

Answer 226

**Underlying linear high signal on T2W images** High T2 signal in the bone underlying an osteochondral lesion has been described as the most common of four MRI ﬁndings indicating instability of an osteochondral fragment, which is the most important factor when considering treatment options. The reported accuracy of this sign for predicting instability varies from 45% to 85%, with one study reporting an increased accuracy when this sign is combined with the second sign of a cartilaginous defect on T1W images. However, another study states that often only a single indicator is present. The other indicators of instability are high signal in the articular cartilage and a cystic lesion in the bed (but this needs to be 5 mm or larger)

Answer 227

**Anterior cruciate and medial collateral ligaments, medial meniscus** O’Donoghue’s unhappy triad consists of injuries to the anterior cruciate and medial collateral ligaments and the medial meniscus, and is an injury associated with contact sports. The mechanism is indirect trauma causing deceleration, hyperextension and twisting forces. The combination of external rotation of the tibia on the femur, knee ﬂexion and valgus stress can produce an anterior cruciate ligament injury combined with additional medial collateral ligament injury. The meniscus and collateral ligament medially are attached to one another, unlike their lateral counterparts, resulting in a higher frequency of concordant injury to the other medial structure when one is injured

Answer 228

Schatzker type 3 Type 1 is lateral condylar split, type 2 is lateral split with depression, type 3 is pure lateral depression, type 4 is medial condylar fracture and depression, type 5 is bicondylar fracture and type 6 is fracture extending to metadiaphysis.

Answer 229

**Shin splints**. Excessive exertion of tibialis and soleus muscles of the legs causes periostitis along the muscular attachments. This **shin splints** results in **longitudinal linear uptake on delayed** bone scan images. The **angiogram and blood pool images are usually normal** compared to: **Stress fracture**, which is associated with **hyper-perfusion and hyperaemia**. On delayed images, focal **fusiform uptake** is seen with stress fracture. Infection is associated with hyper-perfusion, hyperaemia, and focal increased uptake. Osteoid osteoma demonstrates hyper-perfusion, hyperaemia, and focal double density due to nidus and reactive osteosclerosis. Paget’s disease is associated with increased uptake in an enlarged and deformed bone. Age and clinical presentation are also against this diagnosis. Hypertrophic osteoarthropathy is associated with irregular cortical uptake producing the ‘tramline’ sign.

Answer 230

**Stress fracture** This is commonly seen in runners and other athletes, in marching soldiers and in other patients in whom repetitive prolonged muscular action and stress are applied to a bone that is not accustomed to such action.

Answer 231

**Stress fracture** This is the most likely diagnosis as this is a very common site for stress fractures in the feet of runners, especially affecting the second and third metatarsals. Bone scan is almost 100% sensitive showing abnormal uptake within 6–72 hours of injury. MRI is also a very sensitive modality showing intermediate signal intensity on T1 and high signal on STIR and T2- weighted images.

Answer 232

**Focal involvement**. Whilst differentiating these conditions can be difﬁcult and they frequently overlap, there are certain features that can be of value. Neuropathic arthropathy (NA) seldom affects a single bone/ joint in the foot and is most common in the midfoot region. As such a more focal abnormality, or abnormality affecting the metatarsal heads, or other points of pressure, should indicate osteomyelitis. Whilst high T2WI/STIR, low T1WI and enhancement are seen in osteomyelitis, it is also seen in acute neuropathic arthritis and as such is not a good differentiating factor. The converse is not true, where low signal on T1WI and T2WI, typical of chronic NA, would make the presence of osteomyelitis unlikely.

Answer 233

**Plantar ﬁbromatosis** Fibrous masses containing mature collagen are homogenously low in signal on T1WI and T2WI sequences and demonstrate enhancement with gadolinium. Common ﬁbrous masses in the foot are plantar ﬁbromatosis and ﬁbroma of the tendon sheath. Morton’s neuroma is typically intermediate in signal on T1WI and low on T2WI with variable contrast enhancement. Lipomas follow fat signal intensity. They are high on T1WI and T2WI, and low on fat- suppressed sequences. A ganglion cyst follows ﬂuid signal. Ganglion cysts are low on T1WI and high on T2WI with rim enhancement. Haemangiomas are of mixed signal on T1WI and T2WI due to the presence of vessels, fat, and ﬁbrous tissue. The vascular portions of hemangiomas enhance homogenously

Answer 234

**In the normal popliteal fossa, the popliteal artery and vein pass lateral to the medial head of the gastrocnemius and are surrounded by fat**. Popliteal artery entrapment syndrome is a developmental abnormality resulting from an abnormal relationship between the popliteal artery and neighbouring muscles. It is commonly seen in healthy young adults and can present with symptoms of intermittent claudication or thromboembolism. The anatomical abnormality occurs bilaterally in 27–67%. The popliteal vessels normally pass lateral to the medial head of gastrocnemius. An anomalous origin of the medial head or an anomalous course of the popliteal artery may result in extrinsic compression of the artery Doppler and digital subtraction angiography (DSA) ﬁndings may be non-speciﬁc with a wide spectrum of ﬁndings. A normal Doppler or DSA with neutral ankle position does not exclude the diagnosis. Provocative measures with ankle dorsiﬂexion and plantar ﬂexion may be useful in conﬁrming the diagnosis on Doppler and DSA, but they do not demonstrate the underlying anatomical cause. Non-invasive assessment with CT angiogram or MR angiogram is preferred as they also demonstrate the anatomical abnormality.

Answer 235

**Calcaneal fracture classiﬁcation is based on fracture location at the posterior facet**. Calcaneal fractures represent 60% of fractures involving the tarsal bones. Axial loading resulting from a fall from a height is the most common cause followed by motor vehicle accidents. Treatment is based on accurate evaluation and classiﬁcation of calcaneal fractures using multidetector CT reformats. Calcaneal fractures are classiﬁed into **intra-articular and extra-articular based on the involvement of the posterior facet of the subtalar joint.** Intra-articular fractures, accounting for 75% of all calcaneal fractures, are further classiﬁed into four types depending on the number of fracture lines and fragments. Extra-articular fractures are classiﬁed into three types depending on whether the fracture involves the anterior, middle, or posterior aspect of calcaneus. Bilateral fractures are seen in less than 10% of cases. Approximately 10% of calcaneal fractures are **associated with compression injuries of the spine, commonly at the thoracolumbar junction.** Boehler’s angle is formed by the intersection of (a) a line from the highest point of the posterior calcaneal tuberosity to the highest point of the posterior facet and (b) a line from the latter point to the highest of the anterior process. *Normal Boehler’s angle is 20–40°. An angle less than 20° indicates collapse of the posterior facet.** The sustentaculum tali is an eminence on the medial aspect of the calcaneus bearing the middle facet of subtalar joint.*

Answer 236

**None**. This is a complicated question, but one that is frequently posed to musculoskeletal radiologists. A full description is beyond the remit of this section and the reader is referred to the excellent synopsis referenced below. Basically, the foot is divided into the hind foot and fore foot when assessing for congenital abnormalities. The tibio-calcaneal angle (angle made by a line drawn along the length of both bones) should be between 60° and 90°. Less than this is due to abnormal dorsiﬂexion (e.g. as seen with congenital vertical talus, or rocker bottom foot) and more is due to equinus deformity. Secondly, degree of hindfoot varus or valgus is assessed. The talo-calcaneal angle (on a frontal hindfoot x-ray this is the angle between the lines drawn along the length of each bone) should be between 15° and 40°; less is varus deformity and more is valgus. On the lateral view, the fore foot can be roughly assessed with two observations. Normally the metatarsals overlap. However, if the ﬁrst metatarsal is the most plantar, then forefoot valgus is present (as the foot is too ﬂat). If the metatarsals are not superimposed, then varus is present. The ﬁnal step is to remember the features of the common conditions. These are clubfoot (hindfoot equinus and varus), pes planovalgus (hind foot and fore foot valgus, not equinus), and pes cavus (hindfoot valgus).

Answer 237

**Morton’s neuroma** **Low-intermediate on T1 and low on T2** The description is that of a Morton’s neuroma. This occurs most commonly in the **third metatarsal space** and less commonly in the second space. There is often an **associated metatarsal bursitis which is a high signal on STIR imaging**. Ultrasound is usually the first imaging modality; **squeezing the metatarsal heads** together during scanning will usually make the lesion **more prominent.**

Answer 238

**Morton’s neuroma** This is the typical ultrasound appearance of a Morton’s neuroma. Treatment is conservative or surgical removal. On MRI the lesion appears as intermediate signal intensity on T1 and T2. Bursitis is compressible on ultrasound probe pressure

Answer 239

**Second metatarsal and medial cuneiform** The Lisfranc ligament attaches between the second metatarsal and medial cuneiform, which is why an injury to this ligament allows the second to fifth metatarsals to drift laterally once they have lost this stabilisation. This is therefore an unstable injury and requires rapid immobilisation. This is a vital injury to detect as long-term sequelae will often result from a delayed diagnosis.

Answer 240

**Maisonneuve** This is the description of a Maisonneuve fracture (sometimes classified as Weber C3). This injury is often overlooked as the patient may complain only of ankle pain and hence a full tibia/fibula plain film is not taken. This fracture is often associated with ligamentous injury at the ankle, most usually of the anterior talofibular ligament and the postero-inferior talofibular ligament

Answer 241

**E**. Anteromedial ankle impingement syndrome was previously thought to be from eversion injury, but recent studies are showing inversion is the causative injury. There is associated amorphous SI in ATTL with heterotopic bone formation and small corticated ossicles. Post-traumatic synovitis and fibrosis are recognised. The tibialis posterior tendon may be displaced medially

Answer 242

**D** The other answers all belong to the superficial components. The posterior deep tibiotalar ligament is also deep. The superficial and deep components function almost synergistically and stabilise against valgus and pronation as well as rotational force against the talus

Answer 243

**Medial tibial stress syndrome** A spectrum of lesions can occur from repetitive stress. These include periostitis, cortical osteopenia, cancellous bone, and cortical fractures. Injuries are most frequently in the cortex of the distal 2 ⁄ 3 of the tibiae and known as medial tibial stress syndrome.

Answer 244

**Associated proximal fluid filled bursae are seen**. Most commonly between third and fourth metatarsal heads

Answer 245

**Enthesal new bone formation** Most common type of plantar fascia injury. Sharp pain, worse after rest, lessening with exercise. US shows increased calibre > 4mm, loss of reflectivity of the ligament, specifically within the central bundle. MR shows high to intermediate T1 and high T2 SI

Answer 246

**Morton’s neuroma** Morton’s or interdigital neuroma is a benign lesion consisting of perineural ﬁbrosis that entraps a plantar digital nerve. It is frequently asymptomatic, and women represent 80% of cases. Clinical presentation is with foot pain exacerbated by walking, and symptomatic lesions are surgically excised. They are not usually demonstrated on plain radiography and are poorly seen on MRI, returning intermediate T1 and low T2 signal (like surrounding tissues). Typical ultrasound appearances are of a hypoechoic rounded lesion, larger in the axial than the sagittal plane. Ganglia and cysts would return high signal on T2W images, and pathology arising from the tendon sheath itself can also show high signal. Giant cell tumours are usually painless

Answer 247

**Knee** The Maisonneuve fracture is a spiral fracture of the upper third of the ﬁbula associated with a tear of the distal tibioﬁbular syndesmosis and the interosseous membrane. The medial component of the injury may be an associated fracture of the medial malleolus or rupture of the deep deltoid ligament. The ankle joint is effectively a bony ring that extends up to the knee. Interruption of the ring in this way allows lateral displacement of the ﬁbula and so disruption of the congruence of the ankle mortise, resulting in an unstable ankle injury that requires surgical ﬁxation.

Answer 248

**Calcaneo navicular** MRI is valuable in the diagnosis of several musculoskeletal conditions of the ankle, including osteochondral lesions of the talus, bone infarcts and bruising, stress fractures, osteoid osteoma and tarsal coalition. Forty-ﬁve per cent of tarsal coalition occurs at the calcaneo-navicular joint, with a further 45% at the subtalar joint, most commonly involving the middle facet. Radiographic ﬁndings include joint space narrowing, indistinct articular margins, elongation of the anterior calcaneus, a hypoplastic talus and reactive sclerosis of the involved bones. It is commonly associated with pes planus. Treatment options include physical supports, anti- inﬂammatory medication, local steroid injection, and surgical resection or arthrodesis

Answer 249

**Loss of fat signal in the sinus** Sinus tarsi syndrome is a common complication of ankle sprains but may also result from an inﬂammatory arthropathy. It is associated with abnormalities of one or more structures in the tarsal sinus and tarsal canal that led to pain and a feeling of instability of the hindfoot. Most patients with this syndrome present in the third or fourth decade of life with persistent lateral foot pain, though the pathogenesis of the condition is poorly understood. Conventional radiography generally is not valuable, but on MRI there is alteration of the fat signal, the most common changes being diffuse low-signal-intensity inﬁltration on both T1W and T2W images. Other common MR ﬁndings include synovial thickening and diffuse enhancement of the tarsal sinus following intravenous gadolinium.

Answer 250

**Peripheral nerve sheath tumour** The location and direction of mobility along with typical MRI features clinch the diagnosis of peripheral nerve sheath tumour. Ganglion, lipoma and callous would not appear as hyper-vascular lesions. Liposarcoma can show increased vascularity but demonstrates heterogenous enhancement on MRI.

Answer 251

**Plantar fibromatosis** This presents as nodular thickening in the plantar fascia. There can be single or multiple lesions. On MRI, the lesion is low signal on T1 and mild hyperintensity on T2, and the nodule enhances with gadolinium.

Answer 252

**A convex bulge involving the whole of the posterior cortex of the vertebral body**. The others are more in keeping with benign compression fractures. Retropulsion of a posterior fragment into the spinal canal is a highly speciﬁc (100%) ﬁnding of benign compression fracture but has a sensitivity of only 16%. Other features in keeping with malignant compression fractures are complete replacement of normal marrow with low signal on T1WI, involvement of the pedicles, and the presence of an epidural and/or paraspinal soft-tissue mass. The presence of an epidural mass is said to have 80% sensitivity and 100% speciﬁcity for malignant fractures. Convex bulging of the posterior cortex of the vertebra and involvement of the pedicle have respective sensitivities and speciﬁcities of 70% and 94%, and 80% and 94%. Beware that compression fractures due to multiple myeloma only rarely show MRI features of malignant fracture and this diagnosis should be included in the differential of a non-traumatic, benign-appearing vertebral compression fracture.

Answer 253

**Intervertebral vacuum phenomenon** Intervertebral vacuum phenomenon is highly specific for osteoporotic collapse, although it is not common. The other features are all more suggestive of malignancy than osteoporotic collapse. Pedicular destruction occurs in 50% of cases of malignant collapse but in less than 1% of osteoporotic collapse.

Answer 254

**Convex posterior border to the vertebral body** A convex bulge involving the whole posterior border of the vertebral body strongly suggests vertebral body expansion by tumour invasion and is only very rarely a feature of osteoporosis. Other ﬁndings on MRI suggestive of malignancy include a soft-tissue mass, involvement of the pedicles, and heterogeneous high signal on T1W post-contrast or T2W images. Retropulsion of bone fragments, focal T1 low signal or an isointense appearance on T1W or T2W images suggests osteoporotic collapse.

Answer 255

**Degenerative** This is the classical description of the symptoms and radiology of a degenerative spondylolisthesis. Degenerative spondylolisthesis is usually symptomatic due to spinal stenosis and narrowing of neural foramen. This most commonly occurs at the L4/5 level. Spondylolysis is a defect in the pars interarticularis between superior and inferior articulating processes

Answer 256

**Convex posterior cortex** B-E are osteoporotic features. Other malignant features include diffuse low SI on T1, high/heterogeneous SI on T2, and involvement of the posterior elements.

Answer 257

**Right L5** The right L5 nerve root is the most likely to be affected as it will be sitting in the right lateral recess at the L4/5 level. The L4 nerve root will be at the exit foramen and therefore if the protrusion affects only the lateral recess, then this nerve will already have exited and therefore not be affected.

Answer 258

**MRI** Bilateral lower limb involvement suggests a myelopathy rather than a radiculopathy. The presence of urinary and bowel symptoms and saddle anaesthesia suggests compression of lumbosacral nerve roots. This complex of symptoms is cauda equina syndrome and is considered an orthopaedic emergency because of the likelihood of permanent neurological impairment, particularly affecting the autonomic supply to the bladder or bowel, which can result in permanent incontinence if surgery is delayed. The Royal College of Radiologists recommends proceeding straight to MRI in patients who have ‘red ﬂag’ signs.

Answer 259

**Axial T2** The far lateral disc protrusion is the least common type of symptomatic disc herniation. It distinguishes itself from the posterolateral herniation in that the disc ruptures outside the spinal canal, lateral to the root foramen. The disc, instead of tethering the traversing nerve root, compresses the more rostral nerve root that has already exited the root foramen. The neurological symptoms therefore correspond to a lesion at the upper disc level, often leading to confusion in the diagnosis. It is also difﬁcult to diagnose radiologically, as the far lateral location is usually not detected on the sagittal images but only on axial images. STIR is an inversion recovery sequence that suppresses fat and so highlights areas of increased ﬂuid. However, it is not sensitive when the herniation is outside the ﬂuid-ﬁlled spinal canal; therefore, the T2W gradient echo sequence is better at detecting far lateral disc herniation.

Answer 260

**Morquio’s syndrome** Morquio’s syndrome is type IV and the most common of the mucopolysaccharidoses, a family of inherited disorders of metabolism. A central vertebral beak is relatively speciﬁc for the condition. Other spinal manifestations include odontoid hypoplasia with atlantoaxial subluxation (which can be life threatening), platyspondyly, ovoid vertebral bodies, widened intervertebral disc space and exaggeration of the normal lumbar lordosis. Other skeletal ﬁndings include dwarﬁsm, as well as skull, face, and appendicular abnormalities. Hurler’s syndrome belongs to the same family of disorders but has an inferior vertebral beak, which is also seen in achondroplasia and Down’s syndrome. Scheuermann’s disease does not show vertebral beaking.

Answer 261

**Two-column malalignment** The spine can be divided anatomically into three columns: the anterior column contains the anterior longitudinal ligament, anterior half of the vertebral body and anterior annulus ﬁbrosus; the middle column contains the posterior half of the vertebral body, posterior longitudinal ligament, and the posterior annulus ﬁbrosus; and the posterior column contains the posterior elements of the spine, facet joint capsule and interspinous ligaments. Two intact columns are required for intrinsic spinal stability. Disruption of two columns can therefore be used to infer instability. Usual traumatic patterns are anterior and middle, or posterior and middle, disruption Isolated middle column interruption can occur after trauma or surgery, or as a congenital abnormality, and is also considered potentially unstable.

Answer 262

**Paracentral L4/5 disc protrusion** Degenerative disc disease of the spine is one of the leading causes of functional incapacity and chronic disability in the working population, affecting both men and women. Although there is no universally established nomenclature for describing disc herniation, ‘protrusion’ is commonly used if the herniation is broader than it is deep and ‘extrusion’ if it is deeper than it is broad. A disc ‘bulge’ is used to describe a herniation that is very broad based and may even be circumferential, with a generalised disc bulge being one that affects at least half of the periphery. As a result of the strong posterior longitudinal ligament, posterior disc herniation is often paracentral, i.e. to the side of the midline. This can result in compression of the transiting nerve root in the lateral recess, which is the one that will exit at the level below. A lateral disc herniation narrowing the neural foramen compresses the exiting nerve root. Therefore, for a given intervertebral disc, a **paracentral herniation will affect the nerve that exits one level below**, whereas a **lateral protrusion affects the nerve root at that level.**

Answer 263

**Painful osteoid osteoma** Percutaneous cement vertebroplasty is a treatment for vertebral compression fractures that involves the injection of acrylic bone cement into the vertebral body to relieve pain, stabilize fractured vertebrae or, in some cases, restore vertebral height. Current guidelines from the National Institute for Health and Clinical Excellence (NICE), regarding the use of vertebroplasty in the UK, state that it may be used for pain relief in patients with severe painful osteoporosis with loss of height, compression fractures of the vertebral body, symptomatic vertebral haemangioma, and painful vertebral body tumours (metastases or myeloma). Review of current evidence indicates some level of pain relief in 58–97% of patients.

Answer 264

**Atlanto-axial impaction**. This is a more severe form of atlanto-axial subluxation where the C1-2 facets collapse and there is invagination of the dens of C2 into the foramen magnum. As such, the dens is not visible on the lateral radiograph. The key feature, apart from widening of the pre-dental space (which can also be caused by pannus eroding the dens or more commonly atlanto-axial subluxation), is that the anterior arch of C1 lies in front of the lower portion of C2, whereas it normally lies anterior to the dens

Answer 265

**Retropharyngeal space of 10 mm** This is too wide for the retropharyngeal space. The correct acceptable limits for soft-tissue measurements are as follows: * Predental space 3 mm in adults, 5 mm in children. * Nasopharyngeal space (anterior to C1) 10 mm. * Retropharyngeal space (C2–C4) 5–7 mm. * Retro- tracheal space (C5–C7) 22 mm. Disc spaces should be roughly equal throughout the cervical spine. Narrowing of a disc space is usually due to degenerative change but widening would be a more concerning feature.

Answer 266

**Jefferson fractures are usually associated with a neurological deficit** Jefferson fractures are not usually associated with neurological deficit. Although there may be retropulsion of fragments into the vertebral canal, spinal cord injury is rare due to the large dimensions of the canal at this level. Vertebral artery injury, however, must be considered and if there is concern either CTA or MRA imaging should be considered

Answer 267

**Jefferson fracture** Jefferson fracture involves the C1 vertebra. There is a comminuted fracture of the C1 ring, at least through two places. Plain radiography using an open-mouth view demonstrates lateral displacement of the lateral masses.

Answer 268

**Flexion** This describes the typical appearance for a flexion injury as well as the typical mechanism. This would represent a potentially unstable fracture and immobilisation would be essential until further management decisions are made. Flexion teardrop injuries are more common in the lower cervical spine and extension teardrop injuries are more common in the upper cervical spine

Answer 269

**A 7 mm gap between the occipital condyles and the condylar surface of the atlas** This is highly suggestive of cranio-cervical injury; these injuries are often fatal and are often caused by sudden deceleration. Radiologic evaluation of this injury can be difficult but is crucial in determining further management. The remainder of the findings above can all be normal variants in the paediatric cervical spine and therefore should be interpreted with care.

Answer 270

**Jefferson** Unstable fractures include bilateral facet dislocation, flexion teardrop, hangman’s, hyperextension dislocation, Jefferson, odontoid and atlanto-occipital dislocation.

Answer 271

**Hyperextension and traction** The fracture described is a hangman fracture. This involves either the pedicles or pars interarticularis of C2 bilaterally. The mechanism is usually extension and traction (as caused during hanging). Hyperﬂexion injuries produce anterior tear-drop or of a vertebral body wedge fractures. Axial loading can produce a burst fracture of C1 (Jefferson’s fracture) or a vertebral body elsewhere in the spine. Hyperﬂexion and extension are associated with longitudinal ligament injury. Hyper-rotation is associated with soft-tissue injury or facet joint dislocation

Answer 272

**Duodenum** The spinal injury described is a Chance fracture, a fracture through the vertebral body and pedicles caused by hyperﬂexion, therefore causing compression of the spine anteriorly and distraction posteriorly. This injury typically occurs in back-seat passengers wearing a lap seat belt during a road trafﬁc collision. In children, there is a 50% incidence of associated intra- abdominal organ injury. Retroperitoneal organs are most vulnerable, being closest to the spine. Duodenal injuries are most common and have a signiﬁcant associated mortality. The pancreas is also commonly injured due to its retroperitoneal location.

Answer 273

**Sparing of the sacro-iliac joints** Diffuse idiopathic skeletal hyperostosis (DISH) is an ankylosing disorder of the spine. It is most seen in the thoracic region but may involve cervical and lumbar regions. Diagnostic criteria are: **Fowing calciﬁcation** along the anterolateral border of **at least four vertebral bodies** Relative **preservation of intervertebral disc height** **Absence of sacroiliac joint involvement** These three-criteria aid differentiation of spondylosis deformans, intervertebral osteochondromatosis and ankylosing spondylitis respectively. **Extra-spinal manifestations of DISH** include **Achilles tendinosis, tennis elbow**, calcaneal and olecranon enthesopathy and dysphagia. Whiskering is seen radiographically at tendinous insertions, particularly of the pelvis.

Answer 274

**Towne’s** In modern radiology departments with the widespread availability of CT, the indications for skull radiograph are few, and it has little place in the evaluation of brain injury. Standard practice will usually comprise a lateral and a PA frontal view. The frontal view may be angled to show different areas of anatomy. Towne’s view is an AP projection through the frontal and occipital bones (30’ caudal tube tilt) and is mainly used to show the occipital bone. The Caldwell view is a similar AP projection but with only 15’ of caudal tube tilt to allow evaluation of the orbits. An occipitomental (and therefore PA, unlike Towne’s or the Caldwell) projection is called Water’s view. It is used to demonstrate the facial bones and sinuses and may be angulated to highlight the zygomatic arches. Further angulation results in a submento-vertical view, which is also used to evaluate the zygomatic arches. This requires extension of the neck and is therefore contraindicated in patients with suspected cervical spinal injuries. The orthopantomogram is a panoramic view of the mandible used primarily in dental radiography and to evaluate the whole of the mandible in a single exposure.

Answer 275

**Limited joint mobility** A false-negative result in this context is failure to identify pathology and to report incorrectly the ultrasound examination as normal. Limited shoulder mobility will not permit correct positioning of the shoulder for best interrogation of the whole of each tendon and may lead to non-visualization of a tear. Other causes of false negatives include technical factors such as using an incorrect transducer (should be at least 7.5 MHz), poor focusing and poor transducer handling. There are also anatomical causes, including non-diastasis of the tendon ﬁbres, scar tissue, bursitis, tendinosis, and massive tear, with complete retraction of the tendon ends preventing their visualization. Anisotropy, poor transducer positioning or misinterpretation of the rotator interval, musculotendinous junction, supraspinatus–infraspinatus interface, acoustic shadowing and ﬁbrocartilaginous insertion can all give rise to false-positive ﬁndings.

Answer 276

**Small axillary recess** Adhesive capsulitis or frozen shoulder is clinically characterized by restriction of both active and passive elevation and external rotation. Patients are commonly 40–70 years old and predominantly female. It may be idiopathic, preceded by trauma, or associated with diabetes mellitus or other conditions. Patients have been shown to have a signiﬁcantly thickened coracohumeral ligament and joint capsule, and an axillary recess signiﬁcantly reduced in volume. Obliteration of the fat triangle between the coracohumeral ligament and the coracoid process is speciﬁc when seen on MR arthrography. Treatment options include physiotherapy, intra-articular corticosteroid injection, manipulation under anaesthetic and surgical capsulotomy.

Answer 277

**Neer classification** The Neer classification system is used to grade humeral neck fractures. This system describes four parts – greater tuberosity, lesser tuberosity, humeral head and shaft of humerus. According to Neer, a fracture is displaced if there is more than 1 cm of displacement and 45 angulation between any two segments. Two-part fractures involve any of the four parts and include one fragment that is displaced. Three-part fractures include a displaced fracture of the surgical neck in addition to either a displaced greater tuberosity or lesser tuberosity fracture. Four-part fractures include displaced fractures of the surgical neck and both tuberosities.

Answer 278

**Posterior humeral head indentation**. Anterior dislocation occurs when the arm is forcibly externally rotated and abducted. Radiographically, the humeral head lies inferior and medial to the glenoid on the AP view. The Hill–Sachs deformity is an indentation on the posterosuperior portion of the humeral head and indicates a greater likelihood of recurrence. A Bankart deformity is a bony fragment off the inferior glenoid. Anterior humeral head indentation is a ‘reverse Hill–Sachs’ deformity seen in posterior dislocations

Answer 279

**Differentiating partial from full thickness tear**. MR arthrography is most helpful for outlining labral-ligamentous abnormalities in the shoulder and distinguishing partial thickness from full thickness tears in the rotator cuff. The technique involves injection of diluted gadolinium mixed with iodinated contrast, which allows ﬂuoroscopic conﬁrmation of intra-articular needle placement. Partial and full thickness tears may not be distinguishable on standard T1WI because fat and gadolinium have similar signal intensities. This is especially the case when cuff tendons show contrast solution extending to the bursal surface but not deﬁnitively through it. This problem can be overcome with use of fat suppression. MR arthrography should include a T2WI sequence to identify bursal ﬂuid collections and tears. T2WI is also helpful in characterizing incidental bone marrow lesions. Inadvertent injection of gas may lead to a false-positive diagnosis of intra-articular loose bodies, but gas bubbles will rise to non-dependent regions, whereas loose bodies will gravitate to dependent locations. No accurate MR imaging criteria are recognized in the diagnosis of capsular laxity.

Answer 280

**Hill–Sachs lesions are more common than Bankart lesions** A Hill–Sachs lesion affects the postero-superior aspect of the humeral head and whilst it does often indicate a previous dislocation, this is not necessarily the case, and it can be present after a single episode. A Bankart lesion affects the inferior glenoid. Almost 95% of all shoulder dislocations are anterior.

Answer 281

**Adduction and internal rotation** The best position for visualising the supra-spinatous tendon is with the patient’s arm in adduction and internal rotation. Often the patient may be asked to place the back of their hand onto their back, or alternatively asking them to simulate putting the hand into the back pocket of their trousers. The most medial part of the tendon when imaged transversely is the free edge – this is where most supra-spinatous tears occur.

Answer 282

**Type 2 concave pattern is the most common morphology** Type 1-flat (12%) Type 2-concave (56%) Type 3-hooked (29%) Type 4-inferior convex (3%) Type 3 more than Type 2 is associated with increased incidence of rotator cuff tears. ACJ degeneration can narrow the supraspinatus outlet. Significant subacromial subdeltoid (SASD) bursitis include thickness > 3mm, presence of bursal fluid medial to the ACJ and presence of fluid in the anterior aspect of the bursa.

Answer 283

**Tears are classically located at the biceps anchor** SLAP lesions are isolated tears of the glenoid labrum with anterior and posterior components. These lesions occur with repetitive over-arm activity, begin in the posterior aspect of the superior labrum and extend posteriorly.

Answer 284

**Reverse Bankart lesion** The posterior inferior labrum is detected from glenohumeral attachment and there is an avulsion tear of the posterior scapular periosteum

Answer 285

Acutal exam question!! **Normal variant** The ﬁndings describe the Buford complex, a normal variant present in 1.5% of the population. It consists of an absent anterior labrum with a thickened cord-like middle glenohumoral ligament. It can be misdiagnosed as a torn or avulsed anterior labrum, resulting in unnecessary shoulder arthroscopy.

Answer 286

**Axillary nerve palsy** The axillary nerve is a large terminal branch of the posterior cord of the brachial plexus that passes into the posterior aspect of the upper arm via the quadrilateral space, where it winds around the surgical neck of the humerus to supply the deltoid and teres minor muscles. It has a cutaneous distribution called the ‘regimental badge area’ over the lateral aspect of the deltoid (where a soldier may wear his regimental badge). Due to its intimate relationship with the humerus and its passage through the relatively small quadrilateral space, the axillary nerve is by far the most injured nerve with shoulder dislocation or fractures. As loss of abduction may be caused by pain rather than deltoid paralysis, it is good practice to assess the sensation in the cutaneous distribution of the axillary nerve before and after any attempted shoulder reduction

Answer 287

**Posterior shoulder dislocation** Posterior shoulder dislocation is much rarer than anterior dislocation, accounting for only 5% of dislocations. It can be caused by direct or indirect force and is most seen following seizure or electrocution. The internal rotators of the shoulder are stronger than the external rotators, resulting in internal rotation of the arm if all the shoulder muscles contract simultaneously. This internal rotation predisposes to posterior dislocation in the same way that external rotation does for anterior dislocation. Radiographic ﬁndings may be subtle on the AP projection and include superior position of the humeral head relative to the glenoid, external rotation (the humeral head appears symmetrical like a light bulb), a sharp angle to the scapulohumeral arc and a compression fracture of the anterior humeral head (a reverse Hill–Sachs lesion)

Answer 288

**Chemical synovitis** Post-arthrography pain due to sterile chemical synovitis is the most common complication of the procedure, typically beginning after 4 hours and peaking at 12 hours. Other, less common, immediate and short-term complications include allergic contrast reaction (rare in intra- articular injections), introduction of infection and vasovagal reaction.

Answer 289

**Milwaukee shoulder** Milwaukee shoulder is a crystal deposition disease of basic calcium phosphate, predominantly affecting elderly women and resulting in a dysfunctional shoulder from destruction of the rotator cuff. It is often bilateral but always involves the dominant side. Radiographic ﬁndings include superior subluxation of the humerus due to loss of the superior rotator cuff, often forming a pseudarthrosis with the clavicle or acromion. Glenohumeral degeneration manifests as sclerosis and collapse of the humeral head, joint space narrowing and osteophyte formation. Erosion at the site of rotator cuff insertion and periarticular soft tissue calciﬁcation is also a feature. Examination of effusion ﬂuid is stereotypical, revealing spheroid-shaped aggregates of hydroxyapatite crystals. The condition is also seen in the knee, where, unlike osteoarthritis, it predominates in the lateral compartment.

Answer 290

**Coronoid process fracture**. Radial head fractures are common, accounting for approximately one-third of all elbow fractures and up to 5% of all fractures in adults. A recent retrospective study found that associated fracture of the upper extremity was seen in 10.2% of patients, with fractures of the coronoid process the most common (4.1%). Radial head fracture, coronoid fracture, and medial collateral ligament tear form the ‘terrible triad’ of the elbow, which requires operative ﬁxation.

Answer 291

**Fracture of the proximal third**. Scaphoid fracture is the most common of all carpal bone fractures and potentially serious due to the high rate of avascular necrosis. This fracture can be difﬁcult to detect on initial radiographs. Wrist casting and repeat radiography after 1 week are typically advised if there is ongoing suspicion. Fractures of the proximal third account for 20% of injuries but are associated with failure to unite in 90%. Middle third fractures make up the majority (70%), with up to 30% failing to reunite. Distal third fractures usually reunite. A vertical oblique fracture is more unstable than a horizontal oblique fracture. Fracture displacement of greater than 1mm is also a poor prognostic feature.

Answer 292

**Ulnar collateral ligament**. The history and radiographic ﬁndings are typical of gamekeeper’s thumb, which is an injury to the ulnar collateral ligament at its insertion site into the proximal phalanx of the thumb. This injury usually requires internal ﬁxation to secure the ligament. Radial collateral ligament injuries of the thumb lead to painful deformity and articular degeneration. Rupture of ﬂexor pollicis longus results in loss of active ﬂexion of the thumb. The thumb remains in ﬂexion with rupture of extensor pollicis longus. Thumb tendon injuries are typically seen in RA due to their susceptibility to synovitis.

Answer 293

**Scaphoid**. The ﬁndings describe peri-lunate dislocation, which is the most common carpal dislocation. It can occur without fracture (lesser arc injury) or with fracture (greater arc injury). Greater arc injuries are twice as frequent as lesser arc injuries. When describing these injuries, the fracture is named ﬁrst with the preﬁx ‘trans’ followed by the dislocation. Trans-scaphoid peri-lunate dislocation is the most common type of peri-lunate injury. Fractures of the trapezium, capitate, hamate, and triquetrum are also part of the greater arc injuries. Other radiographic signs of this injury include disruption of the carpal (Gilula) arcs and a triangular lunate on the AP view. An early sign is widening of the scaphoid–lunate space (Terry-Thomas sign), which suggests scapholunate dissociation. Lunate dislocation is the ﬁnal stage of peri-lunate injuries and is associated with the highest degree of instability.

Answer 294

**Polyvinyl chloride**. This results in resorption of the middle portion of the terminal phalanx. The other answers cause resorption of the terminal tufts of the distal phalanges. Other causes of resorption of the terminal tuft include Raynaud’s, diabetes, syringomyelia, burns, trauma, epidermolysis bullosa, congenital phenytoin toxicity (in infants of epileptic mothers), and snake and scorpion venom. Hyperparathyroidism can cause tuft, mid-portion, and periarticular resorption; psoriatic arthropathy can cause tuft and periarticular resorption.

Answer 295

**Preiser disease.** The x-ray appearances are typical for osteonecrosis within the scaphoid. This is usually posttraumatic in aetiology, but when idiopathic it is known as Preiser disease. Postulated mechanisms for the osteonecrosis are repetitive minor trauma or secondary to drug treatment (e.g. steroids). The remaining wrong answers refer to osteonecrosis affecting the foot. Freiberg disease affects the head of the second metatarsal, Kohler disease the tarsal navicular, Iselin disease the base of the ﬁfth metatarsal and Sever disease the calcaneal apophysis.

Answer 296

**Scapholunate dissociation** In scapholunate dissociation the scapholunate angle is >60 and there is a >3 mm gap between the scaphoid and lunate on AP view of the wrist. In VISI, capitolunate angle is increased and there is volar angulation of the lunate. In DISI, both scapholunate and capitolunate angles are increased and there is dorsal angulation of the lunate.

Answer 297

**Smith’s fracture** This description is of a Smith’s fracture. More common is a Colles fracture, which is a fracture of the distal radius with dorsal angulation of the distal fragment. A Monteggia fracture is fracture of the ulnar with dislocation of the radial head. A Galeazzi fracture is a fracture of the radius with dislocation of the distal ulnar. Barton’s fracture is a fracture of the distal radius with dislocation of the distal radiocarpal joint.

Answer 298

**Monteggia fracture dislocation** This involves a fracture of the proximal ulna shaft with dislocated radial head

Answer 299

**Abductor pollicis brevis** Abductor pollicis brevis is supplied by the median nerve and would therefore not be affected in an ulnar nerve injury. Due to the anatomic location of the ulnar nerve at the elbow, it can often be damaged leading to denervation and paralysis of the muscles supplied by the nerve. This includes the intrinsic muscles of the hand, which can be very debilitating. Injury to the ulnar nerve at the wrist would lead to severe muscle denervation sparing only the opponens pollicis, the superficial head of the flexor pollicis brevis and the lateral two lumbricals.

Answer 300

**Giant cell tumour of the tendon sheath** This is a benign lesion thought to represent an extra-articular form of pigmented villonodular hyperplasia. This is low signal on both T1- and T2-weighted imaging due to haemosiderin deposition. It most commonly affects the fingers and characteristically lies along a tendon sheath.

Answer 301

**Rolando’s fracture** This is the classic description of a Rolando’s fracture. A Bennett’s fracture is also a fracture of the base of the first metacarpal but with no comminution; this fracture is often less stable than a Rolando’s fracture and more often requires surgical fixation. A ‘gamekeeper’s thumb’ often occurs as the result of forced abduction of the thumb and results in disruption of the ulnar collateral ligament.

Answer 302

**Lunate dislocation** The lesser arc refers to the arc of ligamentous attachments around the lunate. These ligaments become disrupted in a stepwise four-stage fashion. Stage I injury is to the scapholunate ligament, leading to dissociation with rotary subluxation of the scaphoid. Stage II is radiographically characterized by peri-lunate dislocation, caused by additional injury to the capito-lunate joint. The carpus migrates dorsally, and the lunate maintains a normal relationship with the radius. Stage III involves the triquetro-lunate ligaments, and stage IV is complete disruption of the peri-lunate ligaments, allowing dislocation and rotation of the lunate. It is this rotation that creates the triangular outline on AP radiographs. Segmental instabilities relate to the spectrum of dynamic scaphoid instability.

Answer 303

**Wrist** A Galeazzi fracture–dislocation is a pattern of injury sustained by falling on an outstretched hand with a ﬂexed elbow. It most commonly consists of a fracture of the radial diaphysis with dislocation or subluxation of the distal radioulnar joint. It is associated with a high rate of non- union, and one or both components are usually treated with surgical ﬁxation. It is important therefore that the radiologist can recognize potential patterns of injury and radiographically demonstrate their full extent. As a rule, fractures should be viewed in two orthogonal planes, as should the joint above and below any fracture. The opposite pattern, of an ulnar shaft fracture with dislocation of the proximal radial head, is termed a Monteggia fracture–dislocation. A mnemonic for remembering the two is Glasgow Rangers (Galeazzi, radius) and Manchester United (Monteggia, ulna), which indicates for each injury which of the forearm bones is fractured.

Answer 304

**Boutonniere** The Boutonniere deformity is commonly caused by injury or inﬂammatory conditions such as rheumatoid arthritis, and more commonly affects the index than middle ﬁngers. It consists of four stages. Stages 1 and 2 are mild and moderate, passively correctable extension lag, whereas stages 3 and 4 are mild and advanced ﬂexion contractures. The proximal ﬂexion deformity is due to disruption of the central slip of the extensor tendon, with the proximal phalanx herniating through the defect and the lateral slips lying on either side. The position of the proximal phalanx stretches the lateral slips and pulls the distal phalanx into extension. Z-deformity is the name given to a Boutonniere-type deformity seen in the thumb. Swan-neck deformity has similar causes but the opposite conﬁguration, with extension at the proximal interphalangeal joint and ﬂexion distally. Mallet (or baseball) ﬁngers have a passively correctable ﬂexion deformity of the distal interphalangeal joint caused by avulsion of the extensor digitorum tendon by a hyperﬂexion injury

Answer 305

**Radiograph of the chest** Hypertrophic pulmonary osteoarthropathy (HPOA) is a clinical syndrome of osteitis of the long bones, arthritis, and digital clubbing of the ﬁngers and toes. It is most associated with lung cancer (affecting 3–10% of patients) or other chronic pulmonary or pleural disease. The underlying mechanism has not been established with certainty, but autonomic nervous or endocrine stimulation by tumours is postulated, with hormones such as oestrogen, adrenocorticotrophic hormone and growth hormone implicated. In patients presenting with HPOA, approximately 80% have an underlying lung cancer, 10% a pleural tumour and 5% another intrathoracic malignancy. Other causes include chronic, suppurative, pulmonary inﬂammatory disease and congenital cyanotic heart disease. Typical radiographic appearances are of a lamellar periosteal reaction affecting the dia-metaphyseal regions of the long bones, particularly the dorsal and medial aspects. Bone symptoms and radiographic signs frequently regress following treatment of the underlying cause.

Answer 306

**Hypertrophic osteoarthropathy (HPOA) with rib fractures** On bone scan multiple areas of uptake in a linear pattern suggests traumatic injury to ribs. HPOA is characterised by bilateral symmetrical tracer uptake on bone scanning, involving the diaphyseal and metaphyseal regions of long bones. Characteristically a periosteal reaction is seen along the shafts of involved bones. This pattern of uptake is called a ‘double-stripe’ or ‘parallel-track’ sign and is characteristic of HPOA.

Answer 307

**Barton** The use of eponymous names for fractures allows quick and accurate identiﬁcation and communication of bone injuries while simultaneously alerting clinicians to the potential complications associated with a given fracture pattern. This is also particularly useful when describing complex radiographic appearances to someone remote from the images. The full value of such eponyms depends on accurate use and understanding of their meaning: Barton’s fracture–dislocation is an intra-articular fracture of the dorsal margin of the distal radius with dorsal dislocation of the radiocarpal joint; Segond’s fracture is an avulsion fracture of the proximal lateral tibia; Jones’ fracture is a transverse fracture of the base of the ﬁfth metatarsal, at the junction of the diaphysis and metaphysis; Smith’s fracture is a distal radial fracture with ventral displacement; and Hutchinson’s fracture is a triangular fracture of the radial styloid.

Answer 308

**Triquetrum** Carpal fractures in general are much less common than fractures to the distal radius. The two bones most injured are the scaphoid (75%) followed by the triquetrum (14%), and these provide a greater diagnostic challenge radiographically than distal radial fractures. Triquetrum fractures generally occur on the dorsal surface due to avulsion of the dorsal radiocarpal ligament, or shearing forces from impaction with the ulnar styloid or hamate in hyperextension. Less commonly, the body of the bone can fracture in a transverse pattern. A posterior chip fragment can often be seen with dorsal surface fractures but is only visualized on the lateral view. Such an injury may be a primary triquetrum injury (such as avulsion) or related to a peri-lunate fracture–dislocation.

Answer 309

**Non-union of hook of hamate fracture** Fractures of the hook of the hamate are the most frequent type of hamate fracture, and most often occur from the repetitive stress of swinging a bat, club, or racket, or from the direct blow of a club on the ground. This may result in ulnar nerve compression at the wrist in Guyon’s canal, which is particularly exacerbated in the context of non-union due to secondary osteoarthritis or loose bodies in the piso-triquetral joint. Other causes of ulnar nerve compression at the wrist include adjacent masses, anomalous muscles, and tendons, ﬁbrous palmar arch, ulnar artery aneurysm, primary osteoarthritis of the pisotriquetral joint, os hamuli proprium and dislocation of the pisiform bone.

Answer 310

**Ulnar impaction syndrome** Ulnar-sided wrist pain is often caused by one of the spectrums of conditions known as impaction syndromes. These include ulnar impaction syndrome (most common), ulnar impingement syndrome, ulnocarpal impaction syndrome secondary to non-union of the ulnar styloid process, ulnar styloid impaction syndrome and hamato-lunate impingement syndrome. Ulnar impaction syndrome is a degenerative condition secondary to excessive loading across the wrist and characteristically shows a positive ulnar variance that is accentuated in pronation and during a ﬁrm grip. MRI is used to identify complications such as triangular ﬁbrocartilage complex tear or bone marrow oedema.

Answer 311

**Lipoma** The lesion has typical sonographic characteristics of a lipoma.

Answer 312

**Parosteal lipoma** These are benign tumours of adipose tissue which are intimately related to the periosteum. They often contain bony excrescences that may resemble osteochondroma but, unlike osteochondroma, they do not communicate with the medullary cavity of parent bone. MRI is diagnostic, confirming the juxtacortical benign nature of the fatty lesion and non- communication of the bony lesion with the medulla of the adjacent bone.

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