Imaging the Lower Limb Flashcards
For what 3 general reasons might imaging of the lower limb be performed?
- to confirm a clinical suspicion / diagnosis
- to rule out important diagnoses / pathologies
- to guide or evaluate management / treatment
In what 4 scenarios are plain XRs of the LL requested?
In what circumstance are they first line?
- 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
What are plain XRs of the lower limb good for visualising?
What is required to make clinical decisions?
- they are good for visualising:
- fractures
- dislocations
- 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
In what 3 situations might CT of the LL be performed?
- 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
When might an MRI of the LL be performed?
- MRI is performed to image soft tissues such as ligaments, tendons, muscle and cartilage
- e.g. meniscal or cruciate ligament injuries of the knee
What are the following features on an AP pelvic view?
- 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
What is significant about Shenton’s line?
- 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
What injury is shown here?
In what group of people is it common and how can you tell how recent the fracture occurred?
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
What type of fracture is shown here?
Why is this classed as major trauma and what is the immediate treatment?
“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
What type of injury is shown here?
What can cause this and why is it classed as major trauma?
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
What injury is shown here?
vertical shear fracture through the iliac joint
What is meant by a “hip” fracture?
Who do they tend to occur in?
- 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
What are the standard views for a hip fracture?
How might there be rotation in a neck of femur fracture?
- AP
- lateral
- the lesser trochanter is attached to psoas, so internal rotation occurs due to the unopposed pull of psoas on the fractured femoral neck
What is the fovea of the femur?
What is the implication if this is injured in a hip fracture?
- 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
What is shown by the yellow line?
Shenton’s line
How can hip fractures be classified?
- intracapsular
- extracapsular
- 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
What is a subcapital fracture?
- this is a fracture occurring just below the head of the femur
- it is intracapsular as it occurs within the joint capsule
Where can femoral neck fractures occur?
Are they intra- or extracapsular?
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
Where are trochanteric and subtrochanteric fractures found?
- 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
What is the risk associated with intracapsular fractures and how is this managed surgically?
- 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
What is the blood supply to the hip joint?
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)
What can happen to the cruciate anastomosis in fracture of the femoral neck and what does this result in?
- 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
How could this fracture be described?
What precaution needs to be taken?
- 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
How could this fracture be described?
How might this be surgically fixed?
- 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
How could this fracture be described?
- this is an example of a trochanteric fracture (extracapsular)
- these fractures can go through, between or just below the trochanters
What classification system is used for subcapital fractures?
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)
After constant pain in the hip and inability to weight bear, what would be a concern after seeing this XR?
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
What is shown in this image?
- MRI has been used to identify an occult femoral neck fracture that is not visible on plain XR
What are the following features of the femur?
In what group of people to femoral fractures tend to occur?
- femoral fractures tend to occur following low energy falls in the elderly
- massive forces are required to cause femoral fractures in young, healthy adults
How could this fracture be described?
How does it need to be fixed?
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
How could this fracture be described?
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
How could this fracture be described?
In what condition is this more likely to occur?
- this is a comminuted fracture of the distal femoral neck
- more likely to occur in osteopenia when the bone density is low
What are the following features of the knee joint?
What component is NOT part of the knee joint?
- the knee joint is composed of the femur, tibia and patella
- the fibula is NOT part of the knee joint
What are the following components of the knee joint?
What is this view of the called?
When is it used?
skyline view
- it is used to look at the patellofemoral joint and for dislocations
What is shown here?
What anatomical feature is present to prevent this occurring and in what condition is this absent?
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
What is shown in this image?
- this is a normal horizontal beam lateral view
- the patellofemoral joint can be seen
- the quadriceps ligament and patella tendon can also be visualised
What is shown in this image?
What does it imply has happened?
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)
What can be used to help guide decision making when deciding whether to image the knee joint?
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 90o
- patients who cannot weightbear (at least 4 steps) both immediately after the injury and at the time of examination
What XR views of the knee are typically taken?
- standard views are AP and lateral
- a “skyline” view gives a view of the patella
What type of fracture is shown here?
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
How are the tibia and fibula usually fractured?
- 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
What nerve can be injured in a fracture of the fibula?
Why should the fibula be examined when there is an ankle injury?
- 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
What are the features of this AP view of the ankle?
What feature is particularly important to check?
- 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
What are the features of this lateral view of the ankle?
How can the calcaneum be changed in pressure injuries?
- 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
How could this fracture be described?
- fracture through the ditsal fibula (lateral malleolus) with soft tissue swelling
How could this fracture be described?
- there is a fracture of the medial malleolus and through the shaft of the fibula
How could this fracture be described?
Why would it be difficult to fix?
- 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
Ankle injuries commonly present to A&E, but what are most of these caused by?
When should the ankle be imaged?
- 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
What are the Ottawa ankle rules?
- 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
What do the Ottawa ankle rules state about when foot XRs should be taken in conjunction with ankle XRs?
- 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
When should you consider a lower threshold for performing an XR?
- 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
What are the 3 most common ways in which the foot may be injured?
-
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
When are the calcaneus and metatarsals usually fractured?
- 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
What are the bones of the foot?
- green = medial, lateral and intermediate cuneiform bones
- pink = navicular
- blue = talus
- yellow = cuboid
- orange = calcaneum
What are accessory ossicles and what are they often mistaken for?
- 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
