Knee Dislocation


Knee Dislocation, Tibial Femoral Dislocation, Knee Subluxation

  • See Also
  • Background
  1. Uncommon, but potentially limb threatening injury
  • Pathophysiology
  • Causes
  1. Motor Vehicle Accident (two thirds of cases)
  2. Collision Sports (e.g. football, rugby, soccer)
  3. Downhill Skiing
  4. Severe Obesity
    1. Single condition in which Knee Dislocation may occur even without high velocity Trauma
    2. Obesity also complicates the dislocation diagnosis (obscured landmarks) and vascular monitoring
    3. Multiple case studies demonstrating low mechanism dislocations, typically in BMI >40
      1. Popliteal artery injury in 40%
      2. Peroneal nerve injury in 40%
    4. High risk of amputation (as high as 20% of Knee Dislocations)
      1. Ankle brachial index (and CTA if <0.9)
    5. References
      1. Azar (2011) Am J Sports Med 39(10): 2170-4 [PubMed]
      2. Folt (2012) Am J Emerg Med 30(9): 2090.e5-2090.e6 [PubMed]
      3. Georgiadis (2013) J Vasc Surg 57(5): 1196-203 [PubMed]
  5. Total Knee Arthroplasty (TKA)
    1. Anterior dislocation is more common than posterior dislocation
    2. Prevalance of Knee Dislocation after TKA: 0.15 to 0.5%
    3. Causes
      1. Implant malposition
      2. Flexion-Extension gap mismatch
      3. Excessive soft tissue release or laxity
      4. Incorrect primary implant selection
    4. Emergent Management is the same for native Knee Dislocation (see below)
      1. Emergent knee relocation to reduce the risk of neurovascular compromise
      2. Neurovascular exam and evaluation including ABI or CTA as indicated (see below)
      3. Revision of TKA
    5. References
      1. Rashidzada (2020) Crit Dec Emerg Med 34(12): 12-3
  • Types
  1. Most common types
    1. Anterior Dislocation
      1. Severe Knee hyperextension injury (>30 degrees with torn posterior stabilizing elements)
    2. Posterior Dislocation
      1. Direct blow to the proximal tibia (e.g. knee strikes car dashboard in MVA)
  2. Less common types
    1. Medial dislocation
      1. Results from valgus force
    2. Lateral Dislocation
      1. Results from varus force
    3. Rotary Dislocation
      1. Planted foot with counter rotation of the body
      2. May result in a posterolateral dislocation (non-reducible without surgery)
  • Exam
  1. Perform before and after reduction
  2. Knee deformity
  3. Vascular exam (especially popliteal artery distribution)
    1. Perfusion Assessment
      1. Dorsalis pedis pulse
      2. Posterior tibial pulse
      3. Capillary Refill
      4. Ankle-Brachial Index (ABI)
        1. Normal ABI (as well as pulses, Capillary Refill) may not exclude popliteal artery disruption
    2. Hard signs of vascular injury
      1. Distal pulse loss or ischemia (e.g. pallor, coolness)
      2. Active bleeding
      3. Expanding hematoma
      4. Palpable thrill or bruit over popliteal artery
  4. Neurologic Exam (especially peroneal nerve)
    1. First web space and dorsal foot sensation
    2. Ankle dorsiflexion
  5. Multidirectional instability
    1. Multidirectional instability may be only finding if knee spontaneously reduced prior to presentation
    2. Three of four ligaments are likely injured (ACL Tear, PCL Tear, LCL tear, MCL tear)
  6. Skin changes
    1. Dimple Sign
      1. Anteromedial skinfold at medial joint line
      2. Seen in posterolateral dislocation (not reducible without surgery)
    2. Skin necrosis
      1. Entrapped skin at femoral condyle
    3. Overlying Laceration
      1. Suggests open Knee Dislocation (accompanies 20-30% of Knee Dislocations)
  • Imaging
  1. Knee XRay
    1. Pre-reduction
      1. Do not delay reduction for imaging if any signs of vascular compromise
      2. Evaluates for Fracture
    2. Post-reduction
  2. Vascular Ultrasound
    1. Arterial Doppler Ultrasound
  3. CT Angiogram
    1. Indicated post-reduction if signs of vascular compromise (popliteal artery disruption)
    2. Critical Limb Ischemia requires emergent vascular surgery without delay of angiogram (see below)
  • Precautions
  1. Knee Dislocation is a surgical emergency requiring immediation reduction
  2. Delay in reduction risks limb-threatening vascular compromise
  3. Pre-reduction imaging is only indicated if no signs of vascular compromise
  4. Knee spontaneous reduction prior to presentation
    1. Do not dismiss patient report of "popping out and in sensation" simply as Patella subluxation
    2. Multidirectional instability may be only finding if knee spontaneously reduced prior to presentation
    3. Knee Dislocation may occur with low energy mechanism and confers much higher risk than Patella subluxation
    4. Follow the same vascular evaluation and monitoring if Knee Dislocation is suspected
  5. Have a high index of suspicion for vascular injury (popliteal artery) in up to 20-40% of patients
    1. Vascular injury may be present in up to 9% of cases despite normal distal pulses (high risk of amputation)
      1. Confirm with ABI and Doppler Ultrasound
      2. Obtain CT Angiogram if Ankle-Brachial Index <0.9
    2. More than 50% of Knee Dislocations spontaneously relocate prior to emergency department presentation
      1. Follow post-reduction plan below
  1. Perform knee reduction without delay
  2. Procedural Sedation
  3. Technique (requires 2 providers)
    1. One provider grasps the distal femur to stabilize
    2. Other provider grasps the proximal tibia
      1. Avoid compression at the popliteal fossa (popliteal artery)
      2. Apply longitudinal traction to tibia
      3. Reverse the dislocation if traction alone does not reduce the dislocation
        1. Continue longitudinal traction
        2. Push the tibia posteriorly in anterior dislocation
        3. Pull the tibia anteriorly in posterior dislocation
  4. Splint knee after reduction
    1. Apply Knee Immobilizer or long leg splint
    2. Prevents repeat dislocation in the acute period
    3. Splint in 20 degrees flexion
  5. Failed reduction
    1. Emergent orthopedic Consultation
    2. Posterolateral dislocations are not reducible without surgery
  6. Emergent Surgical Intervention Indications
    1. Prolonged ischemia or other hard signs of vascular injury (see exam above)
    2. Knee reduction fails (e.g. posterolateral dislocation) or cannot be maintained
    3. Open Knee Dislocation
  • Management
  • Evaluate for vascular compromise (popliteal artery injury)
  1. No vascular injury
    1. Findings
      1. Strong dorsalis pedis pulse and posterior tibial pulse
      2. Ankle-Brachial Index >0.9
      3. Bedside arterial duplex Ultrasound normal
    2. Management
      1. Observation hospital stay
      2. Serial distal vascular examinations
      3. Observe for distal extremity paleness, Paresthesias, paralysis
      4. Orthopedic Consultation for reconstructive surgery
  2. Possible vascular injury
    1. Findings
      1. Adequate limb perfusion despite abnormal vascular findings
      2. Asymmetric dorsalis pedis pulse or posterior tibial pulse
      3. Ankle-Brachial Index <0.9
      4. Bedside duplex Ultrasound abnormal
    2. Management
      1. Urgent vascular surgery Consultation
      2. Urgent CT angiogram (or other angiographic assessment of popliteal artery)
  3. Vascular compromise (limb-threatening)
    1. Findings
      1. Weak or absent dorsalis pedis pulse and posterior tibial pulse
      2. Signs of limb ischemia or vascular injury
    2. Management
      1. Emergent vascular surgery Consultation for immediate repair
  • Complications
  1. Popliteal artery injury (32-40% of Knee Dislocations)
    1. Results in limb threatening vascular injury
    2. Popliteal vein injury may also occur
    3. Devascularization results in nearly 100% amputation rate at 8 hours
  2. Peroneal nerve injury (14-35% of Knee Dislocations)
    1. Results in loss of first web space and dorsal foot sensation
    2. Results in loss of ankle dorsiflexion and toe extension
  3. Lower leg Compartment Syndrome
    1. Late finding if due to popliteal artery injury
  4. Deep Vein Thrombosis
  5. Tibial Plateau Fracture
  6. Tibial shaft Fracture
  7. Fibular Head Fracture
  8. Severe knee ligamentous disruption
  • References
  1. Grozenski and Kiel (2019) Crit Dec Emerg Med 33(10):10-1
  2. Mason and Campagne in Herbert (2018) EM:Rap 18(3):12-3
  3. Bachman in Wolfson and Stack (2014) Knee Dislocation and Reduction, UpToDate, accessed 6/5/2014
  4. Kelleher in Brenner (2013) Knee Dislocation, Medscape Emedicine, accessed 6/5/2014