Imaging the Lower Limb

Question 1

For what 3 general reasons might imaging of the lower limb be performed?

Answer 1

• to confirm a clinical suspicion / diagnosis
• to rule out important diagnoses / pathologies
• to guide or evaluate management / treatment

Question 2

In what 4 scenarios are plain XRs of the LL requested?

In what circumstance are they first line?

Answer 2

• if there is clinical suspicion of / to exclude a fracture
• if there is clinical suspicion of / to exclude a dislocation
• if there is clinical suspicion of inflammation / infection
  
  • e.g. septic arthritis, gout, OA, RA, osteomyelitis
• they are first line in ongoing / worsening bony pain

Question 3

What are plain XRs of the lower limb good for visualising?

What is required to make clinical decisions?

Answer 3

• they are good for visualising:

1. fractures
2. dislocations
3. joint spaces

• …but more than one view of the area of interest is required
• they can also reveal areas of thickening and thinning of bone

Question 4

In what 3 situations might CT of the LL be performed?

Answer 4

• if X-ray is equivocal
• if X-ray is normal but there is ongoing clinical suspicion
  
  • e.g. evaluating the midfoot for a Lisfranc fracture dislocation - which is difficult to see on plain XR
• if detailed anatomical information is needed in complex fractures** and **surgical planning

Question 5

When might an MRI of the LL be performed?

Answer 5

• MRI is performed to image soft tissues such as ligaments, tendons, muscle and cartilage
  
  • e.g. meniscal or cruciate ligament injuries of the knee

Question 6

What are the following features on an AP pelvic view?

Answer 6

• the pubic symphysis is a cartilagenous joint that is very strong
• the pubic rami form a ring around the obturator foramen
• obturator internus and externus are on the inside and outside of this ring
• the obturator vessels pass through the obturator foramen a they travel from the pelvis to the medial side of the thigh

Question 7

What is significant about Shenton’s line?

Answer 7

• it runs along the inferior aspect of the neck of the femur and superior pubic ramus
• if this is not a solid line, it suggests there is a fracture

Question 8

What injury is shown here?

In what group of people is it common and how can you tell how recent the fracture occurred?

Answer 8

fracture of the pubic rami

• there are both superior and inferior fractures present here
• Shenton’s line is disrupted
• this injury is common in elderly patients as a result of a fall
• these are old fractures as they have slightly sclerotic margins
  
  • this happens when there is an ununited fracture that hasn’t healed

Question 10

What type of fracture is shown here?

Why is this classed as major trauma and what is the immediate treatment?

Answer 10

“open book” fracture

• there is disruption of the pubic symphysis and the ligaments holding it there, causing the pelvis to “spring open”
• common in motorcycle injuries
• there is a risk of bleeding to death due to disruption to / tearing of the pelvic veins (not bleeding from the fracture)
• the pelvis is held in place by external compression until the patient can reach theatre

Question 11

What type of injury is shown here?

What can cause this and why is it classed as major trauma?

Answer 11

vertical shear fracture (through sacroiliac joint & sacrum with diastasis of pubic symphysis)

• on examination, one leg will be shorter than the other as one hip is higher than the other
• there is a risk of rupture to the pelvic veins, which can result in bleeding to death
• this usually happens in trauma where all of the force travels through one leg

Question 13

What injury is shown here?

Answer 13

vertical shear fracture through the iliac joint

Question 14

What is meant by a “hip” fracture?

Who do they tend to occur in?

Answer 14

• a “hip fracture” is a fracture of the femoral neck or proximal femur
• they tend to occur in elderly people after low energy trauma / falls
• a hip fracture in a young / healthy adult would require high energy trauma

Question 15

What are the standard views for a hip fracture?

How might there be rotation in a neck of femur fracture?

Answer 15

1. AP
2. lateral

• the lesser trochanter is attached to psoas, so internal rotation occurs due to the unopposed pull of psoas on the fractured femoral neck

Question 17

What is the fovea of the femur?

What is the implication if this is injured in a hip fracture?

Answer 17

• it is an oval-shaped dimple on the head of the femur
• the ligamentum teres attaches to the fovea
• if the blood supply through the ligamentum teres is disrupted, this can result in avascular necrosis of the femoral head

Question 18

What is shown by the yellow line?

Answer 18

Shenton’s line

Question 19

How can hip fractures be classified?

Answer 19

1. intracapsular
2. extracapsular
3. trochanteric

• this depends on whether the fracture occurs within or outside of the region of the joint capsule
• a trochanteric fracture is extracapsule and occurs through the trochanteric region

Question 20

What is a subcapital fracture?

Answer 20

• this is a fracture occurring just below the head of the femur
• it is intracapsular as it occurs within the joint capsule

Question 21

Where can femoral neck fractures occur?

Are they intra- or extracapsular?

Answer 21

Transcervical:

• a transcervical fracture occurs midway across the neck
• this type of fracture is intracapsular

Basicervical:

• a basicervical fracture occurs across the base of the neck
• this can be intracapsular or just extracapsular

Question 22

Where are trochanteric and subtrochanteric fractures found?

Answer 22

• trochanteric fractures occur between / through the trochanteric region
• subtrochanteric fractures occur below the trochanters
  
  • these are technically fractures of the proximal femoral shaft
• these are both examples of extracapsular fractures

Question 23

What is the risk associated with intracapsular fractures and how is this managed surgically?

Answer 23

• in an intracapsular fracture, there is a risk of disruption to the blood vessels in this region
• this can result in avascular necrosis and death of the head of the femur
• a hemiarthroplasty is performed and the head of the femur is removed to eliminate this risk
• extracapsular fractures do not have the risk of avascular necrosis

Question 24

What is the blood supply to the hip joint?

Answer 24

cruciate anastomosis

• the profunda femoris gives rise to the medial and lateral circumflex arteries
• the medial circumflex artery is the primary supply to the joint as it gives the branches that enter the joint capsule to supply the femoral head
• there is also a contribution from the inferior gluteal artery (from internal iliac)

Question 25

What can happen to the cruciate anastomosis in fracture of the femoral neck and what does this result in?

Answer 25

* fracture of the femoral neck can **_tear the medial circumflex artery_** * this leads to loss of the blood supply to the head of the femur, resulting in **_avascular necrosis_**

Question 26

How could this fracture be described? What precaution needs to be taken?

Answer 26

* this is a **_subcapital fracture_**, which is **intracapsular** * as it is intracapsular, there is a risk of **disruption of the blood supply to the femoral head** * due to the **risk of AVN**, **_hemiarthroplasty_** needs to be performed

Question 27

How could this fracture be described? How might this be surgically fixed?

Answer 27

* this is a **_subtrochanteric fracture_** (proximal femoral) that is **extracapsular** * a **_dynamic hip screw_** is used in extracapsular fractures * some wires would also need to be used to hold the lesser trochanter in place * in an ideal scenario, bone ends are **positioned together but are still able to move** slightly as this stimulates fracture healing

Question 28

How could this fracture be described?

Answer 28

* this is an example of a **_trochanteric fracture_** (extracapsular) * these fractures can go through, between or just below the trochanters

Question 29

What classification system is used for subcapital fractures?

Answer 29

**_Garden classification_** **_Garden I:_** * **incomplete** subcapital fracture **_Garden II:_** * complete but **undisplaced** fracture (normal trabecular lines across joint) **_Garden III:_** * complete and **partially displaced** fracture (interruption of trabecular lines) **_Garden IV:_** * complete and **fully displaced** fracture (interruption of trabecular lines)

Question 30

After constant pain in the hip and inability to weight bear, what would be a concern after seeing this XR?

Answer 30

**_occult fracture_** of neck of femur * these are not easily diagnosed on radiograph * if they are missed, the non-displaced fracture **may become displaced** * **_MRI_** is the best tool to diagnose occult fractures, but often **CT is performed first** as it is easier to request and much quicker

Question 31

What is shown in this image?

Answer 31

* MRI has been used to identify an occult femoral neck fracture that is not visible on plain XR

Question 32

What are the following features of the femur? In what group of people to femoral fractures tend to occur?

Answer 32

* femoral fractures tend to occur following **_low energy falls in the elderly_** * massive forces are required to cause femoral fractures in young, healthy adults

Question 33

How could this fracture be described? How does it need to be fixed?

Answer 33

**_transverse fracture_** through the **shaft of the femur** * there is **overlapping** of the fracture, which leads to **shortening of the leg** * it needs to be **pulled apart** before the **ends are placed together** and a plate or intermedullary nail is used to fix it

Question 34

How could this fracture be described?

Answer 34

**_spiral fracture_** of the femoral neck * a spiral fracture occurs as a result of a **_twisting force_**, creating a fracture line that wraps around the bone like a corkscrew * this is much more **unstable** and will slip more easily * it is more difficult to fix and will require a **nail down the centre of the bone** * this is likely to be a **pathological fracture** as the bone is permanently eroded and supple

Question 35

How could this fracture be described? In what condition is this more likely to occur?

Answer 35

* this is a **_comminuted fracture_** of the distal femoral neck * more likely to occur in **osteopenia** when the bone density is low

Question 36

What are the following features of the knee joint? What component is NOT part of the knee joint?

Answer 36

* the knee joint is composed of the **femur, tibia and patella** * the **_fibula is NOT part of the knee joint_**

Question 37

What are the following components of the knee joint?

Answer 37

Question 38

What is this view of the called? When is it used?

Answer 38

**_skyline view_** * it is used to look at the **patellofemoral joint** and for **dislocations**

Question 39

What is shown here? What anatomical feature is present to prevent this occurring and in what condition is this absent?

Answer 39

**_subluxation of the patella_** * the **_lateral condyle is larger_** than the medial condyle to prevent sideways dislocation of the patella * the pull on the patella is to **pull laterally when straightening the leg** * in **hypoplasia of the lateral condyle**, there is **_frequent dislocations_ of the patella**

Question 40

What is shown in this image?

Answer 40

* this is a **normal horizontal beam lateral view** * the patellofemoral joint can be seen * the quadriceps ligament and patella tendon can also be visualised

Question 41

What is shown in this image? What does it imply has happened?

Answer 41

**_lipohaemarthrosis_** * this is the presence of **_fat and blood_** in an effusion * fat is lighter than blood so will float on top and produce a line between the 2 layers * this indicates an **injury to the knee joint** has caused **leaking of fat and blood** * this is usually an **_occult fracture_** or **_avulsion of a ligament_** that has pulled a small amount of bone off (e.g. cruciate ligament injury)

Question 42

What can be used to help guide decision making when deciding whether to image the knee joint?

Answer 42

**_Ottawa knee rules_** * patients **aged \>55** * patients with **isolated patellar tenderness** * patients with **fibular head tenderness** * patients who are **unable to flex the knee to 90^o** * patients who **cannot weightbear** (at least 4 steps) **both immediately after the injury** and **at the time of examination**

Question 43

What XR views of the knee are typically taken?

Answer 43

* standard views are AP and lateral * a "skyline" view gives a view of the patella

Question 44

What type of fracture is shown here?

Answer 44

**_tibial plateau fractures_** * this involves a break in the **cartilagenous surface of the knee joint** * it is **rare to only break the bone**, and often the meniscus, ligaments, muscles, tendons and skin around the knee are also involved * they can be easily missed if subtle so be aware of **_tenderness over the tibial plateau / swelling of soft tissues_**

Question 45

How are the tibia and fibula usually fractured?

Answer 45

* the tibia is usually fractured after a **direct below** or **from a fall** * **_the fibula is often injured in conjunction with the tibia_** - if one fracture is seen then look for the other * the fibula is often injured as a result of a **twisting injury** or by **repeated stress**

Question 46

What nerve can be injured in a fracture of the fibula? Why should the fibula be examined when there is an ankle injury?

Answer 46

* fracture of the fibular neck can injure the **_common peroneal nerve_** * the **proximal fibula** should be examined when there is an ankle injury as **_fracture of the medial malleolus_** can cause proximal fibular fractures via **transmitted forces**

Question 47

What are the features of this AP view of the ankle? What feature is particularly important to check?

Answer 47

* the fibula is always located laterally * it is important to look at the **_joint spaces / alignment at the mortise_** as the **distance all the way around this should be _equal_**

Question 48

What are the features of this lateral view of the ankle? How can the calcaneum be changed in pressure injuries?

Answer 48

* the calcaneum has a ***"honeycomb centre"*** that becomes **_flattened_** in pressure injuries * landing on the heel with a high impact leads to a **crush fracture** and **loss of height**

Question 49

How could this fracture be described?

Answer 49

* fracture through the ditsal fibula (lateral malleolus) with soft tissue swelling

Question 51

How could this fracture be described?

Answer 51

* there is a fracture of the medial malleolus and through the shaft of the fibula

Question 52

How could this fracture be described? Why would it be difficult to fix?

Answer 52

* the fracture involves the **medial malleolus, tibia** and **shaft of the fibula** * the **_ankle mortise is abnormal_** as the distance all the way around is not equal * this is an example of an **_intra-articular fracture_** * as soon as the fracture goes into the joint, there is **loss of congruity** and it is **difficult to fix back into alignment** * intra-articular fractures also **_predispose to arthritis_**

Question 53

Ankle injuries commonly present to A&E, but what are most of these caused by? When should the ankle be imaged?

Answer 53

* most ankle injuries are **_inversion injuries resulting in ligament sprains_** * these are **painful on weight-bearing** and cause significant **swelling around the lateral malleolus** * the ankle should only be injured when there is **_suspicion of a fracture_** * the **_Ottoawa ankle rules_** help clinicians decide whether XR is necessary after ankle injury

Question 54

What are the Ottawa ankle rules?

Answer 54

* the patient is **_unable to weight-bear_** for 4 steps both **immediately after injury** and **at the time of assessment** * or they have **tenderness** over the **_posterior surface of the distal 6cm_** (or tip) of the **_lateral or medial malleolus_**

Question 55

What do the Ottawa ankle rules state about when foot XRs should be taken in conjunction with ankle XRs?

Answer 55

* there must be **trauma to the midfoot** and **pain** and * **_tenderness_** **over the** **_navicular_** or **_base of the 5th metatarsal_** OR * patient **_cannot weight-bear_** for 4 steps both **immediately after the injury** and at the **time of assessment**

Question 56

When should you consider a lower threshold for performing an XR?

Answer 56

* patients who are **difficult to assess properly** (intoxicated, agitated, learning difficulties) * when **severe swelling** prevents proper palpation of the bones * if patients have **reduced sensation** or other "distracting" injuries

Question 57

What are the 3 most common ways in which the foot may be injured?

Answer 57

* **avulsion fractures of the 5th metatarsal** * *this happens when an inversion injury pulls the base of the MT off* * *the fibularis tendon attaches here* * **fatigue ("stress") fractures** of the metatarsals (usually 2nd or 3rd) * *occurs when someone does a lot of walking* * *there is a periosteal reaction but often a fracture line is not seen* * fractures of the **phalanges**

Question 58

When are the calcaneus and metatarsals usually fractured?

Answer 58

* fracture of the calcaneus most commonly results from a **_fall from height directly landing on the heel(s)_** * the metatarsals tend to be fractured when **_heavy objects fall onto or run over the foot_**

Question 59

What are the bones of the foot?

Answer 59

* green = medial, lateral and intermediate cuneiform bones * pink = navicular * blue = talus * yellow = cuboid * orange = calcaneum

Question 60

What are accessory ossicles and what are they often mistaken for?

Answer 60

* they are **extra bits of bone around the ankle** that are a **normal variation** * they are often **mistaken for fractures** * they are **_well-defined bone_** with **_clear cortical margins_** around the outside * avulsed parts of bone tend to have **_poorly-defined margins_** (unless they are chronic injuries) and are likely to be **_tender_**