see also:

• the acutely injured knee in ED
• trauma

• an important time critical red flag of the acutely injured knee in ED is the possibility of a knee dislocation having occurred (not a patellar dislocation), as this requires urgent investigation to exclude a possible vascular injury to the popliteal vessels and potential
• knee dislocation is uncommon and mainly occurs with high energy injuries such as motor vehicle accidents, falls from a height, high impact sports, downhill snow skiiing, etc.
• knee dislocations are an increasingly common complication of gym exercises such as:
  • falling awkwardly when doing hamstring stretches with foot caught on bar
  • leg presses with heavy loads eg. 200kg single leg press
• most dislocations are clinically evident and require urgent reduction as they may be limb threatening due to vascular injury
• some spontaneously reduce but there is still potential vascular injury which needs emergent assessment.

• popliteal artery injury
  • after 8 hours of ischaemia, most will require an above knee amputation!!!
  • lesions or thrombosis may not become clinically apparent for several weeks after injury
• compartment syndrome of the leg
• common peroneal nerve injury
• associated injuries include ACL/PCL/meniscal/collateral ligt/tibial plateau fracture/tibial shaft fracture/proximal fibular fracture
• DVT
• late onset complications:
  • pseudoaneurysm
  • arthosis
  • stiffness
  • chronic pain

• an anteromedial skin furrow suggests posterolateral dislocation and these are irreducible by closed reduction methods due to buttonholing of the femoral condyle - these patients need urgent open reduction
• other dislocations:
  • if good peripheral pulses, consider pre-reduction imaging
  • if peripheral pulses impaired, immediate reduction in ED is indicated to save the limb.

• care and precautions as per usual ED Mx of conscious sedation
• two clinicians required to reduce the knee while a third manages airway, sedation, etc
• one clinician grasps femur, the other the tibia - avoid applying pressure in popliteal fossa as this may exacerbate vascular injury
• apply longitudinal traction, and most will reduce
• if unsuccessful, reverse the direction of the dislocation
• if still unsuccessful, urgent ortho team consult

• check for signs of vascular injury
• document popliteal and pedal pulses - but note that presnce of pulses does not exclude injury!
• consider measuring the ankle-brachial index (ABI)
• consider urgent doppler USS
• if any vascular injury present, urgent consult with vascular surgeon
• post-reduction plain Xrays
• many advocate routine CT angiography after any knee dislocation given the poor sensitivity of physical examination
• admit all patients
• 3-4hrly neurovascular obs for at least 24 hours
• post-discharge instructions:
  • repeat Xrays within 1 week to confirm still reduced
  • patient to return ASAP if any vascular symptoms
  • close orthopaedic follow up to determine need for and timing of surgical reconstruction of knee joint

• presence of a significant posterolateral corner injury which is suggested by either:
  • fibular styloid fracture on lateral Xray (“arcuate sign”) is pathognomic of posterolateral corner injury and note that this is a different fracture to a fibular head fracture
  • Segond avulsion fracture from the tibial condyle on AP Xray is associated with ACL injury and posterolateral corner injury
  • Medial Segond avulsion fracture from the medial tibial condyle on AP Xray is associated with PCL injury and posterolateral corner injury
  • External Rotation Recurvatum Test:
    • The great toes are held by the examiner as both legs are raised simultaneously. A positive test results in hyperextension, external rotation of the tibia, and apparent tibia vara of the affected limb.
  • the Dial Test:
    • This test is performed with the knee flexed at 30deg and 90deg. The patient may be supine or prone.
    • The thighs are stabilized by an assistant or a strap, while the lower legs are synchronously externally rotated.
    • The amount of external rotation at the tibial tuberosity is compared with the other side. If prone, the external rotation may be measured by the thigh-foot angle. An increase of 10 to 15 degrees is considered a positive test and suggests a significant posterolateral corner injury.