Trauma Imaging of Lower Limb Flashcards
What are lower limb fractures associated with?
High morbidity and mortality
Immobility = pneumonia, DVT/PE, dehydration/starvation
What are the limitation of x-rays when imaging fractures?
Can’t visualise through overlapping structures
May not be shown on standard x-ray projection
Fracture is undisplaced
Can’t capture soft tissue structures
Why are CT scans useful for imaging fractures?
Cross sectional = unaffected by overlapping structures and can show fractures irrespective of their plane
Why are MRI scans useful for imaging fractures?
Provides detailed info about bone marrow so can show undisplaced fractures
What techniques can be used to image soft tissue injuries?
US = high resolution images of superficial structures, especially tendons MRI = high resolution images of all structures, even those deep inside body or within joints (areas where US struggles)
What are some features of lower limb fractures?
Often involve axial force with bone impaction = may appear sclerotic
Typical sites of impacted fracture = femoral neck, tibial plateau, calcaneus
What are some features of high energy pelvic ring fractures?
Often young people, associated with RTA or fall from height
Bony ring disruption usually affects more than one site so usually multiple (either bones of symphysis)
How are high energy pelvic ring fractures imaged?
X-ray if pelvis is only site of injury
CT is primary test for polytrauma patients
What are some features of low trauma pelvic fractures?
Affect elderly patients with osteoporosis, typically due to minor fall or may be of insidious onset
Multiple fractures often present = typically sacrum and pubic rami
How are low trauma pelvic fractures typically imaged?
X-rays often normal = CT better than x-ray especially once fractures start to heal
MRI is better than CT so is test of choice
What are some features of pelvic soft tissue injuries?
Sports related
Acute causes = muscle tear or tendon avulsion
Chronic overuse can cause bone/soft tissue pain at site of tendon/ligament attachment
How are pelvic soft tissue injuries imaged?
US = shows acute injuries affecting superficial structures MRI = gold standard, provides more complete assessment of all soft tissues and bones
What are some features of an acute hamstring tendon avulsion?
Commonly sports related, cause of acute pelvic injury
What are some features of a hip dislocation?
Result of RTA or contact sport where hip is flexed
Typically posterior, with acetabular rim fracture
May be complicated by femoral head AVN or early OA
How are hip dislocations imaged?
CT = details anatomy to help with surgical planning
What are the two classifications of proximal femoral fractures?
Intracapsular and extracapsular
What are some features of intracapsular proximal femoral fractures?
Interfere with blood supply to femoral head
Prone to femoral head AVN or non-union
Treated by hemiarthroplasty = young patients or undisplaced fractures may be fixed with reduction and screw fixation
What are some features of femoral shaft fractures?
Usually high energy and obvious on x-rays
Carry risk of blood loss or fat embolus
What kind of injuries are more common in the knee?
Soft tissue injuries
How is imaging used in knee injuries?
Ct used to clarify fracture anatomy
US and MRI used to assess soft tissue
What do small avulsed bone fragments indicate in the knee?
Significant soft tissue injury
What soft tissue structures are shown by the lateral view of the knee?
Patellar and quadriceps tendons
Suprapatellar fat space
What are significant soft tissue injuries in the knee normally accompanied by?
Effusion = fills the suprapatellar space
What is the standard trauma x-ray taken for the knee?
AP (horizontal beam lateral) = can show lipohaemarthrosis which is a sign of an intra-articular fracture
What are some features of a knee dislocation?
Often largely reduced by time of x-ray so check bony alignment
Results in complex soft tissue disruption
Has potential for vascular injury (popliteal artery)
What are some features of a tibial plateau fracture?
80% affect lateral condyle
Follow valgus force with foot planted
Variable appearance = from obvious fracture line to subtle subchondral sclerosis
How are CTs used to treat tibial plateau fractures?
Show are of condylar involvement and depth of depression which guides treatment
What can be used to visualise extensor mechanism injuries of the knee?
US = clarifies quadriceps and patellar tendon tears
What can be used to show acute intra-articular injuries of the knee?
MRI = can see through swelling
What are some soft tissue injuries of the knee that MRI can be used to visualise?
Meniscal tears, capsular and ligamentous injuries, hyaline cartilage damage, subtle fractures
What do the menisci of the knee do?
Spread load between femur and tibia
What causes meniscal tears?
Twisting injuries = tear causes pain and can become displaced causing “locked knee”
What do the ACL and MCL do?
Important stabilisers of knee
What are some features of hyaline cartilage injuries?
Can predispose to early OA, invisible on x-rays
MRI can define extent of injury and any resulting loose bodies, as well as success of surgical repair
What do the tibia and fibula form with the talus?
The paired bones form an elongated ring with the talus = disruption may be remote from each other
How is the ankle normally injured?
Via inversion or eversion
How are x-rays used in ankle trauma?
Part of initial assessment = AP and lateral views
How are CT, MRI and US used in ankle trauma?
CT used to clarify fracture anatomy
MRI and US needed to define soft tissue injury
Why do children get different fractures form adults?
The have growth plates and soft bones
What does a non-uniform ankle joint indicate?
Instability = often has ligament damage
What are some features of malleolar fractures?
Usually solitary, often small avulsion fractures or undisplaced
How many views are undisplaced fractures usually visible on?
Only one
What are some features of ankle fractures?
Often multiple, usually affect lateral and medial malleoli and posterior malleolus (posteroinferior tibia)
What causes a talar dome margin fracture?
Excessive inversion or eversion = often subtle fracture invisible on x-ray, may need MRI to diagnose, cause of chronic pain and instability
What are some features of a fifth metatarsal base fracture?
Follows inversion and resembles lateral malleolar fracture
Transvers = easily confused with normal adolescent longitudinal ossification centre
What are some features of calcaneal fractures?
Follows axial compression = fall from height onto heel
Causes loss of peak (Bohler’s angle) and increased bone density, often comminuted
Anatomy clarified by CT
What are some fracture mimics?
Accessory ossification centres and sesamoid bones
What are some examples of accessory ossification centres?
Fifth metatarsal base = in teens, longitudinal ossification centre at base
Fragmented posterior ossification centre = normally seen along posterior calcaneus in children
Os trigonum = commonly seen on posterior talus
What are some examples of sesamoid bones?
Fabella = within lateral head of gastrocnemius, often visible posterior to distal femur
Rounded sesamoid bones = found throughout, especially on medial and lateral plantar aspects of first metatarsal head
What is the most common ankle tendon to be affected in an injury?
The Achilles tendon
What may cause a tendon tear in the ankle?
Sometimes follows single high energy event
Often culmination of recurrent minor tears
What are risk factors for ankle tendon injuries?
Diabetes, RA, steroid use
What is used to determine between partial and complete ankle tendon tears?
US or MRI
US often easier for patients and allows dynamic assessment, especially of Achilles
What are the standard views of the midfoot?
AP and oblique
What are some features of TMT joint fracture/subluxation?
Subtle, can cause long term disability
What is key to diagnosing TMT joint injury (Lisfranc)?
Alignment = assess first and second TMT congruity on AP view, and third to fifth TMT congruity on oblique view
What are the characteristics of a Lisfranc injury?
Involve several TMT joints, with multiple ligamentous avulsion fractures = shown best by CT
