Orthopaedics - Hip

Question 1

What risk factors are associated with hip arthritis?

Answer 1

Loss of cartilage at the hip joint causes pain and stiffness as bony surfaces of the femoral head and the acetabulum come into contact.

More common in over 50s, with “wear and tear”. In some patients there are predisposing factors:

• inflammatory arthritis (RA, SLE, psoriatic arthritis) - systemic conditions that may affect multiple joints
• osteonecrosis - results in collapse of the femoral head
• previous septic arthritis - enzymes produced by bacteria destroy cartilage. Active infection is a contraindication to joint replacement
• abnormal hip shape - hip dysplasia, old slipped femoral epiphysis (SCFE), femoroacetabular impingment and old Perthe’s disease are developmental conditions that alter shape of the “ball and socket joint” causing increased wear. Patients develop OA in their 4th decade.

Question 2

What signs and symptoms are associated with hip OA?

Answer 2

Pain: groin, buttock or thigh pain. Initially only present with movement but eventually becomes constant, even preventing sleep

Stiffness: typically patients are unable to cross their legs and getting out of a low chair or car is difficult

Limp: combination of pain, stiffness and weak muscles around hip result in a limp and the classic Trendelenburg gait

Question 3

What are the key features on examination of a patient with hip OA?

Answer 3

Gait assessment and comment on stick or frame

Trendelenburg test whilst the patient is standing to assess hip ABDUCTORS

Range of movement - first do Thomas’ test to exclude a fixed flexion deformity, then assess all movements compared to the contralateral side: flexion, extension, abduction and adduction, internal and external rotation with the hip extended and in flexion

Leg length - erosion of the acetabulum may cause true shortening; fixed abduction contracture may cause apparent shortening

Neurovascular examination of the legs (feel for pulses and sensation), brief assessment of lumbar spine

Question 4

What differential diagnoses should be considered in patients with suspected hip OA?

Answer 4

Spine: mechanical back pain may cause buttock or groin pain. Radiculopathy (root impingement) may cause shooting pains down the back of the leg, usually extending below the knee

Knee: pathology can cause thigh pain or limping

Tumour: primary bone tumours are rare, bony metastases are common. Weight loss, history of cancer (esp. breast and prostate), constant pain or night pain are red flags. Obtain full length femoral X rays or bone scan

Infection: septic arthritis and osteomyelitis, patient systemically unwell

Stress fracture of femora neck seen in runners; subtrochanteric fractures occur in elderly patients on bisphosphonates due to inhibition of bone remodelling

Greater trochanteric bursitis: inflammation of the bursa between iliotibial band and the greater trochanter may cause sharp localised pain. Patients typically cannot lie on their side.

Question 5

What investigations should be requested in patients with suspected hip OA?

Answer 5

X rays - AP pelvis and lateral of the affected hip. Look for LOSS signs. Comment on leg length and the position of the femoral head in the acetabulum. Lumbar spine, full length femur and knee may also need X rays.

Bloods - routine pre op bloods if surgery is planned, CRP, ESR and RhF/ ANA if inflammatory arthritis suspected

CT/MRI - CT is good at assessing bone loss if acetabulum is severely eroded. MRI assesses soft tissues around the hip as well as the state of the cartilage if the diagnosis is not clear

Question 6

What are the treatment options for OA?

Answer 6

Weight loss, analgesia, activity modification
Physiotherapy and use of a stick
Total hip replacement

Question 7

What is osteonecrosis?

Answer 7

Loss of blood supply to bone is known as osteonecrosis. All joints can be affected but the femoral head is at risk because its blood supply is retrograde and tenuous.

Question 8

What can cause femoral head osteonecrosis?

Answer 8

Idiopathic - most cases
Trauma - intracapsular neck of femur fractures disrupt the retinacular blood vessels that supply blood to the femoral head
Steroids - alterations in fat metabolism result in lipid globules in the blood, which block arterioles
Long term alcohol use
Haemaglobinopathies (e.g. sickle cell anaemia)
The bends - divers ascending too quickly develop nitrogen bubbles in the blood, which may block arterioles

Question 9

What is the pathophysiology of avascular necrosis of the femoral head?

Answer 9

Bone just below the cartilage (subchondral bone) is the most susceptible to die if blood supply is disrupted. Initially patient complains of pain in the hip, but X rays appear normal. After a period of 3-6 months, dead subchrondral bone appears dense on X ray. Several weeks thereafter, the dead bone is resorbed and a linear lucency develops. This is known as the crescent sign. If the patient continues weight bearing, the femoral head collapses, losing its spherical shape and resulting in secondary osteoarthritis.

Question 10

What is the treatment for avascular necrosis of the femoral head?

Answer 10

Initially, make patient non weight bearing to prevent femoral head collapse. Physio maintains ROM

Core decompression: early cases, before crescent sign appears, tunnel is drilled up the femoral neck and into the head, relieves pressure, improves blood flow and may stimulate bone healing. Results not guaranteed

THR: once head has collapsed this is the only surgical option

Question 11

When is total hip replacement indicated?

Answer 11

Usual indication is treatment of hip OA when conservative treatment has failed and symptoms are severe enough to warrant surgery.

Question 12

How many types of hip replacement are there?

Answer 12

3 types:
1) Total hip replacement - femoral head is replaced with a prosthetic ball and the acetabulum is relined with a prosthetic cup

2) Resurfacing - technique in which the patients femoral head is preserved and resurfaced with a metal shell. The acetabulum is relined in the same way as THR. Preservation of bone makes future revision easier, but realignment very sensitive to errors with even small deviations resulting in femoral neck fractures. Failure rates are high and technique is not as popular
3) Hemi-arthroplasty - replacement of the femoral head only, without addressing acetabulum. Used for treatment of femoral neck fractures

Question 13

What is the difference between a cemented and an uncemented hip replacement?

Answer 13

Prosthesis may be secured to bone using bone cement. This is a polymer called polymethylmethacrylate. It acts as a grout and is injected into the femoral canal under pressure to ensure it becomes deeply embedded into the prepared bone surface. Pressurisation may force fat out of the marrow and into the bloodstream, can cause intraoperative hypotension and cardiovascular collapse during the procedure.

Alternatively an uncemented prosthesis may be used. These prosthesis are coated in hydroxyapetite (same chemical compound as calcium and phosphate found in bone) and have a roughened surface to encourage bone to integrate with the prosthesis creating a “biological bond”. Theoretically this is longer lasting than cement and avoids the issues associated with fat embolism. But the tight fit required may result in fractures of the femur or pelvis as the prosthesis is implanted.

Question 14

What is a bearing surface?

Answer 14

The interface between the ball of the femoral head and the cup of the acetabulum is known as the bearing. The bearing carries significant load and must be low friction and hard wearing. If the bearing wears out then the hip has to be revised.

Question 15

What different materials can be used for bearing surfaces?

Answer 15

1) Polyethylene - used in the acetabulum, cheap and low friction. Wear out with time, producing debris in the form of polyethylene particles. These small particles are the same size as bacteria, and this similarity stimulates white blood cells to produce inflammatory cytokines. Cytokines stimulate osteoclast to resorb bone around the prosthesis, causing loosening and premature failure. This is called osteolysis.
2) Metal - cheap and works well with polyethylene acetabular liners. Metal was used as the acetabular bearing, but resulted in large amounts of metal wear debris being produced and caused problems with systemic toxicity and local inflammation
3) Ceramic - hard wearing and extremely low friction. Good material for both acetabular liners and femoral heads. So hard that there is virtually no wear, making it good for young patients. It is expensive and can fracture if exposed to sudden shock loading

Question 16

What complications are associated with total hip replacement?

Answer 16

1) Nerve injury - sciatic nerve is particularly at risk resulting in foot drop and numbness in the foot. Common causes include traction on the nerve or compression by retractor placement
2) Bleeding - average is 250ml
3) DVT - without prophylactic anticoagulation DVT is common after THR. Chemical and mechanical thromboprophylaxis should be used
4) Infection - clean air supply in theatre, antibiotic loaded cement and perioperative antibiotics. If the prosthesis becomes infected a two stage revision may be indicated in which the hip is removed, the patient is given antibiotics for 6 weeks before a new prosthesis is inserted
5) Dislocation - may occur if soft tissues are not balanced or the prosthesis is malpositioned intraoperatively. Precautions including avoidance of crossed legs, bending over and sitting in low chairs
6) Leg length discrepancy - if the acetabulum has been severely eroded or the hip is an abnormal shape, leg length differences are more common. Up to 15mm difference is usually well tolerated.

Question 17

How should a painful THR be investigated?

Answer 17

Infection - this is the first diagnosis to exclude. Infection may occur many years after surgery. It may be due to bacteria introduced at the time of surgery, or haematogenous spread of bacteria in conjunction with an infection elsewhere in the body such as a dental abscess. Check CRP and ESR and get a bone scan, which will show increased uptake around the prosthesis.

Loosening - may be due to polyethylene debris osteolysis or infection. X ray signs of loosening include a lucent line around the prosthesis or migration of the prosthesis on serial views

Fracture - may occur intraoperatively, especially with uncemented implants, or post operatively following a fall. If the femoral stem is loose it needs to be revised; if it remains fixed in the femur, cables and a plate can be used to reconstruct the bone around the stem

Other diagnosis - if the patients pain has not got better after THR was it the right diagnosis?

Question 18

What is developmental dysplasia of the hip?

Answer 18

DDH is a condition in which the femoral head does not lie within the acetabulum. It is a spectrum of disease ranging from a femoral head that sits reduced for most of the time but can be pushed out of the acetabulum, often with a palpable or audible “clunk” (known as “clicking hip”) to a hip that is subluxed (partial contact remains between the head and acetabulum), to the most severe form where the hip is dislocated and irreducible.

Failure to obtain congruent reduction in a child means that the femoral head will not grow spherically and the acetabulum will not form properly. In later life this can lead to leg length discrepancy, abnormal gait, arthritis and pain.

Question 19

What risk factors are associated with DDH?

Answer 19

Breech position
First born
Oligohydramnios - these three risk factors restrict the space in the uterus for foetal development
Female sex - higher levels of oestrogen result in increased ligamentous laxity
Family history - 6% if normal parent, 12% if affected parent, 36% if affected sibling AND parent

DDH is commonest in the left hip because this is usually the side of the foetus that presses against the mothers spine. DDH is also associated with torticolis and metatarsus adductus. Collectively these conditions are known as packaging disorders, resulting from restricted uterine space. It is thought that 1 in 60 neonates in the UK may have a degree of DDH, but most of it resolves spontaneously by 6 weeks.

Question 20

What clinical signs are associated with DDH?

Answer 20

Gluteal fold asymmetry - poor sensitivity but sometimes noted by healthcare workers or parents when changing nappies

Abduction range - a very simple test to check the range of abduction of both hips. Asymmetry raises concerns

Barlow’s test - detects a hip that can be dislocated posteriorly. Flex hip and knee to 90 degrees and gently axially load, feeling for a clunk. Barlow’s push Backwards!

Ortolani’s test - this test detects a hip that is already dislocated and can be reduced. Flex the hip and knee to 90 degrees and keep your index finger on the greater trochanter. Abduct the hip gently and exert gentle forward pressure with your finger, feeling for the hip popping back into the joint. Ortolani’s Open legs!

Galeazzi test - flex hip and knees to 90 degrees and look from side for difference in patellar height indicating leg length discrepancy

Question 21

What imaging is required in DDH?

Answer 21

The superior ossific nucleus of the femur, which will go on to form the femoral head, does not appear on x ray until around 6 months of age, therefore X rays are of limited use for this age group.

Ultrasound: not only does it detect cartilagenous structures, it is dynamic, meaning that real time screening can be performed as the hip is moved around. The scans can be difficult to interpret but the key measurement is the angle between the the bony roof of the acetabulum and the iliac wing. This is known as the alpha angle. Normal values should be greater than 60 degrees. An angle less than this indicates the acetabulum is shallow and is less likely to keep the femoral head in the joint.

Arthrogram - if doubt remains about whether the hip is transiently dislocating, subluxed or permanently dislocated, an arthrogram can be performed. Under anaesthetic, contrast is injected into the joint space and the hip is screened under fluoroscopy in a variety of positions

Question 22

When are X rays useful in DDH?

Answer 22

In children over 6 months of age, the femoral head can be seen as a small dot. Two lines are drawn on X ray; Hilgenreiner’s line across the triradiate cartilages of the acetabulae; Perkin’s line perpendicular to Hilgenreiner’s line passing through the lateral edge of the roof of the acetabulum. The head should be in the inferomedial quadrant formed by these two lines. Shenton’s line can be traced and should be unbroken.

Question 23

How should DDH be treated in a child of under 6 months of age?

Answer 23

A Pavlik harness is a device that holds the hips reduced. Straps keep the hip flexed and abducted. Too much flexion risks femoral nerve injury, too much abduction risks avascular necrosis of the femoral head. The harness should be worn for 23 hours per day. Reduction should be confirmed with USS. The usual duration of treatment is 6 months.

Question 24

How should DDH be treated in a child between 6 months and 2 years?

Answer 24

In this age bracket ALL children should have an examination under anaesthetic and arthrogram in order to determine if any structures are blocking concentric reduction.

If the hip is reduced with the leg in a safe position (avoiding extremes of abduction or flexion) a hip spica cast can be applied for a total of 3 months. If the hip is irreducible or only reduced in an extreme position, open reduction may be required. Most surgeons will defer this until the child is 18 months of age because the risk of surgery is less in older children.

Question 25

How should a child with DDH over the age of 2 years be treated?

Answer 25

Children of this age need open reduction because the acetabulum will be full of fibrofatty tissue (pulvinar), the joint capsule will be stretched and baggy and there may be tendons interposed in the joint space. Surgery aims to remove obstacles to reduction and tighten up the capsule. Sometimes a femoral osteotomy is also required.

In children who present beyond 4 years of age, the acetabulum may be so shallow and poorly formed that a pelvic osteotomy must be performed to deepen and reorientate the acetabulum with the aim of improving coverage of the femoral head.

Question 26

What is Perthe’s disease?

Answer 26

This is ideopathic osteonecrosis of the femoral head. As the head loses its blood supply it generates pain. As the dead bone collapses, the head loses its spherical shape.

Question 27

What risk factors are associated with Perthe’s disease?

Answer 27

Typically Caucasian boys aged 4-8 years are affected. The male:female ratio is 5:1. Risk factors are small stature, immature bone age, and living in a poor urban environment with exposure to passive smoking. There is also an association with thrombophilia and other clotting abnormalities, implying that the disease is caused by interruptions to blood supply. 15% may be bilateral.

Question 28

What symptoms does Perthe’s disease present with?

Answer 28

Pain is the hip or groin. There is often an associated limp. Occasionally, pain is referred to the knee.

Question 29

What investigations should be performed in Perthe’s disease?

Answer 29

Imaging should include an AP pelvis and frog let lateral X ray of the hips (the child abducts and flexes the legs like a frog). The disease follows a chronological pattern that can be seen on x ray:
1) Initial stage - the X ray may be normal. Occasionally a widened joint space may be seen, representing an effusion in the hip joint. As the disease progresses, sclerosis of the head may be seen

2) Fragmentation - dead bone is resorbed resulting in subchondral fractures and the crescent sign. The extent of femoral head involvement can be evaluated at this stage and this reflects the prognosis - the more the femoral head is involved, the worse the prognosis
3) Reossification - new bone is laid down. This process may take up to 18 months
4) Remodelling - the head remodels until skeletal maturity. If it has remained well contained within the acetabulum, and the child was young at age of onset, it may remodel to a spherical shape conveying a much better prognosis

Question 30

What determines prognosis in Perthe’s disease?

Answer 30

There are 3 main factors that determine the risk of arthritis and long term pain.
1) Age of the child - a younger child has more chance to remodel and will therefore do better. Children over 6 years old at onset have a poorer prognosis

2) The extent of femoral head involvement - if more of the femoral head is involved, the outcome is worse. The lateral one third of the femoral head is the main weightbearing section. If this has significantly collapsed, arthritis may result
3) Abduction contracture - if the hip loses significant abduction, remodelling will be limited and the outcome less favourable

Question 31

What is the treatment for Perthe’s disease?

Answer 31

Most cases are treated conservatively with activity modification and periods of partial weight bearing when the hip is painful. In the past, braces and traction were used but these have not been shown to improve long term results.

The disease should be carefully monitored for loss of abduction and decreased range of movement as this may indicate that the head is no longer contained within the acetabulum. X rays should be performed periodically,. If the head is no longer contained within the cup, surgery is indicated. This may be a femoral osteotomy, a pelvic osteotomy or a combination of both.

Question 32

Slipped capital femoral epiphysis

Answer 32

Weakness in growth plate of femoral head –> femoral neck slipping on femoral head (used to be called slipped upper femoral epiphysis, SUFE)

Question 33

How is SCFE classified?

Answer 33

Chronicity or stability:

1) Chronicity
- acute: symptoms for less than 3 weeks
- chronic: symptoms for more than 3 weeks
- acute on chronic: background pain with sudden exacerbation

2) Stability
- slip is stable if child can weight bear, with or without crutches
- unstable if child cannot weight bear
- unstable slips have 50% risk of avascular necrosis, not a problem in stable slips

Question 34

Risk factors for SCFE

Answer 34

Aged 10-16 years
Male sex
Obesity 
Afro-Carribean origin
Endocrinopathy including hypothyroidism and hypogonadism
Positive family history

25% bilateral

Question 35

Symptoms and signs of SCFE

Answer 35

Limp and groin pain

Pain is referred to knee (any child in this age group with unexplained knee pain should have hip X rays)

Question 36

Investigations in SCFE

Answer 36

X rays

• AP pelvis and frog leg lateral (most sensitive)
• Follow Klein’s line (= trace superior border of the femoral neck and extrapolate it beyond the growth plate); should intersect the lateral third of the femoral head; SCFE head slips below Klein’s line

Question 37

Treatment for SCFE

Answer 37

“Pinning in situ” - prevent slips from progressing further
- single screw passed across the growth plate to anchor it in position

Open reduction and internal fixation severe slips
- complex; risk of avascular necrosis

High risk of slippage on contralateral side, prophylactic pinning considered

• child under 10
• known endocrinopathy

Question 38

What is transient synovitis?

Answer 38

Hip pain, mimics septic arthritis - “irritable hip”
History - child 2-5 years, sudden onsent hip pain and limp
- associated with gastroenteritis or viral URTI

Hip develops effusion, child holds hip flexed and externally rotated, unwilling to move it

Question 39

Investigations in transient synovitis

Answer 39

CRP, ESR - mild elevation

FBC - normal WCC (child usually afebrile)

Question 40

Treatment of transient synovitis

Answer 40

Self limiting, responds well to NSAIDs

Question 41

Differentiation between septic arthritis and transient synovitis

Answer 41

Kocher criteria:

• WCC > 12
• inability to bear weight
• fever >38.5
• ESR > 40

4 positive criteria have 99% predictive value for septic arthritis, 3 criteria 93%, 2 criteria 40%, 1 criteria 3%.

US guided aspiration can confirm diagnosis