Knee radiograph (an approach)

Knee radiograph (an approach)

Systematic review

Effusion?

Check for an effusion on the lateral:

 Tibiofemoral alignment
  • draw a line down the lateral margin of the lateral femoral condyle
  • if > 5 mm tibia is observed outside the line, think tibial plateau fracture
Plateau review
  • carefully look for a proximal tibial fracture
  • pay particular attention to:
    • tibial spine: avulsion
    • lateral tibial plateau: small avulsion (Segond fracture)
    • areas of increased density may point to underlying fracture
    • medial epicondyle: don't overcall calcification adjacent to the medial femoral epicondyle (Pellegrini-Stieda lesion)
Patella
  • fractures are usually easy to spot
  • don't call a bipartite patella a fracture: well-corticated unfused center at the superolateral pole
  • check for patella tendon disruption
    • patella tendon: inferior pole of patella to tibial tuberosity
    • patella tendon length = patella length ± 20%

Common pathology

Lipohemarthrosis
  • fat and blood from bone marrow collect in suprapatellar bursa
  • a fat-fluid level may be the only sign of intra-articular fracture
  • associated with tibial plateau or distal femoral fractures
  • more: lipohemarthrosis
Tibial plateau fracture
  • 80% involve the lateral plateau
  • fall from height or car bumper impact
  • associated significant cruciate and medial collateral ligament damage
  • more: tibial plateau fracture
Segond fracture
  • avulsion fracture; bony fragment adjacent to lateral tibial plateau
  • internal rotation and varus stress; falls or sports
  • 75% associated with anterior cruciate ligament injury
  • more: Segond fracture
Intercondylar eminence fracture
  • typically avulsion fracture of tibial attachment of anterior cruciate ligament
  • mechanism: rapid deceleration or hyperextension of the knee
  • most common in adolescents
  • more: intercondylar eminence fracture
Patella fracture
  • majority transverse, also vertical or comminuted
  • direct blunt force or violent contraction of quadriceps
  • oblique or skyline views will confirm fractures
  • more: patella fracture
Distal femoral fracture
  • 6% of all femur fractures
  • bimodal distribution
  • high energy blunt trauma; falls in elderly
  • more: distal femoral fracture
Proximal fibula fracture
  • typically occur with lateral tibial plateau fractures, but may be isolated
  • varus force
  • associated with lateral collateral ligament damage
  • more: proximal fibula fracture

Don't miss...

Pellegrini-Stieda lesion
  • post-traumatic soft-tissue calcification adjacent to medial epicondyle of femur
  • ossification following injury to medial collateral ligament
  • do not misdiagnose as a fracture
  • more: Pellegrini-Stieda lesion
Approaches to radiographs