Knee Dislocations

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Introduction

• Usually from a high-impact injury (tackle while leg planted); 
• Outside of sports medicine, we typically see in trauma setting with dashboard injuries
• Nearly 75% of ligaments will be disrupted 
• Associated Injuries:
  • Vascular
    • 5-15% in all dislocation with nearly have occurring in A/P dislocations
  • Nerve
    • Common peroneal nerve injury in 25% of cases!
      • S: Decreased sensation over dorsum of foot sparing the lateral most portion
      • M: loss of dorsiflexion/eversion of the ankle; Loss of EHL -> Foot drop
  • Fractures presenting 60% of cases with femur and tibia being most common 

 
Signs & Symptoms

• Symptoms = Knee pain/instability (brought to knees)
• PE:
  • No deformity!
    • 50% of knee dislocations will spontaneously reduce prior to arrival; very deceptive
  • Swelling, effusion, abrasions
  • Obvious deformity
    • Reduce immediately!!!
• Make sure you assess all ligaments (ACL, PCL, MCL, LCL)
• Vascular exam is key!
  • Number one priority
  • Need to do both BEFORE and AFTER reduction
  • DP/PT pulses 
    • If pulses present/normal àDoes NOT rule-out arterial injury; collateral circulation can mask complete popliteal artery occlusion
    • ABI time!
      • >0.9 = serial examinations
      • <0.9 = CT angiography; consult vascular surgery if needed
    • Diminished/Absent Pulses:
      • Make sure knee is reduced!
      • Time = Muscle
      • IMMEDIATE surgical consult if pulses are still absent following reduction or hard signs of vascular compromise (expanding hematoma, distal ischemia, thrill)
      • Ischemia >8 hours has amputation rate ~85%
  • Pulses present after reduction àABIs àObservation vs angiography

 
Classification

• Kennedy classification for direction of displacement of tibia on femur; Schenck for ligaments
• Anterior
  • Most common (30-50%)
  • Hyperextension injury and usually requires PCL to tear
• Posterior
  • 2ndmost common (25%)
  • Due to axial load on a flex knee
  • *Highest rate of vascular injury, i.e. complete popliteal artery tear
• Lateral and Medical
  • Due to varus/valgus force
  • Lateral dislocation has highest change of peroneal nerve injury

 
Diagnostics:

• XR ànormal if spontaneous reduction
• Look for other fractures (Segond)
• Non-emergent MRI
• CT angiography as above

Treatment:

• Reduce and re-exam!

• This is an ORTHOPEDIC/SPORTS EMERGENCY
• There is one situation where reduction of the knee should not take place.  The “dimple sign” represents buttonholing of the medial femoral condyle through the anterior medial joint capsule.  The sign indicates an irreducible dislocation and closed reduction is contraindicated for the risk of skin necrosis.
• Posterior:
  • Someone holds distal femur, provider pulls longitudinally then anteriorly
  • Be careful; too much force can cause popliteal injury
• Anterior:
  • Counter-traction on proximal tibia
• Once reduced, splint in 20-30 (deg) flexion and re-shoot films
• Most cases require surgical stabilization, consult your orthopedic surgeons
• If ABI >0.9 with strong pulses and normal doppler -> Admit for observation
• ABI <0.9 with asymmetric pulses or abnormal doppler -> consult vascular surgery, obtain CTA