https://upload.orthobullets.com/topic/1043/images/Xray - Lat - knee dislocation (emedicine)_moved.jpg
https://upload.orthobullets.com/topic/1043/images/Clinical photo - recurvatum (emedicine)_moved.jpg
https://upload.orthobullets.com/topic/1043/images/MRI - coronal - knee dislocation (emedicine)_moved.jpg
  • Devastating injury resulting from high or low energy
    • high-energy
      • usually from MVC or fall from height
      • commonly a dashboard injury resulting in axial load to flexed knee
    • low-energy
      • often from athletic injury
      • generally has a rotational component 
      • morbid obesity is a risk-factor
  • Pathoanatomy
    • associated with significant soft tissue disruption
    • 3/4 of ligaments generally disrupted
  • Associated injuries
    • vascular injury
      • 5-15% in all dislocations
      • 40-50% in anterior/posterior dislocations 
      • due to tethering at the popliteal fossa
        • proximal - fibrous tunnel at the adductor hiatus
        • distal - fibrous tunnel at soleus muscle
    • nerve injury
      • usually common peroneal nerve injury (25%)
      • tibial nerve injury is less common
    • fractures
      • present in 60%
      • tibia and femur most common
  • Prognosis
    • complications frequent and rarely does knee return to pre-injury state
  • Descriptive
    • Kennedy classification based on direction of displacement of the tibia post
      • anterior (30-50%)
        • most common 
        • due to hyperextension injury
        • usually involves tear of PCL
        • arterial injury is generally an intimal tear due to traction
      • posterior (25%)
        • 2nd most common 
        • due to axial load to flexed knee (dashboard injury)
        • highest rate of vascular injury (25%) based on Kennedy classification (direction of dislocation)
        • highest rate of complete tear of popliteal artery
      • lateral (13%)
        • due to varus or valgus force
        • usually involves tears of both ACL and PCL
        • highest rate of peroneal nerve injury
      • medial (3%)
        • varus or valgus force
        • usually disrupted PLC and PCL
      • rotational (4%)
        • posterolateral is most common rotational dislocation
        • usually irreducible
        • buttonholding of femoral condyle through capsule
  • Schenck Classification
    • based on pattern of multiligamentous injury of knee dislocation (KD)
Schenck Classification (based on number of ruptured ligaments)
KD I Multiligamentous injury with involvement of ACL or PCL
KD II Injury to ACL and PCL only (2 ligaments)
KD III Injury to ACL, PCL, and PMC or PLC (3 ligaments). KDIIIM (ACL, PCL, MCL) and KDIIIL (ACL, PCL, PLC, LCL). KDIIIM has highest rate of vascular injury (31%) based on Schenck classification
KD IV Injury to ACL, PCL, PMC, and PLC (4 ligaments)
KD V Multiligamentous injury with periarticular fracture
  • Symptoms
    • history of trauma and deformity of the knee
    • knee pain & instability
  • Physical exam
    • appearance
      • no obvious deformity
        • 50% spontaneously reduce before arrival to ED (therefore underdiagnosed)
        • may present with subtle signs of trauma (swelling, effusion, abrasions)
      • obvious deformity
        • reduce immediately, especially if absent pulses
        • "dimple sign" - buttonholing of medial femoral condyle through medial capsule
          • indicative of an irreducible posterolateral dislocation 
          • a contraindication to closed reduction due to risks of skin necrosis 
    • stability
      • diagnosis based on instability on exam (radiographs and gross appearance may be normal)
      • may see recurvatum when held in extension 
      • assess ACL, PCL, MCL, LCL, and PLC
    • vascular exam
      • priority is to rule out vascular injury on exam both before and after reduction
        • serial examinations are mandatory
        • palpate the dorsalis pedis and posterior tibial pulses
      • if pulses are present and normal 
        • does not indicate absence of arterial injury 
          • collateral circulation can mask a complete popliteal artery occlusion
        • measure Ankle-Brachial Index (ABI) post   
          • if ABI >0.9  
            • then monitor with serial examination (100% Negative Predictive Value)
          • if ABI <0.9
            • perform arterial duplex ultrasound or CT angiography
            • if arterial injury confirmed then consult vascular surgery
      • If pulses are absent or diminished 
        • confirm that the knee joint is reduced or perform immediate reduction and reassessment
        • immediate surgical exploration if pulses are still absent following reduction  
          • ischemia time >8 hours has amputation rates as high as 86%
        • if pulses present after reduction then measure ABI then consider observation vs. angiography
  • Radiographs 
    • may be normal if spontaneous reduction 
      • look for asymmetric or irregular joint space
      • look for avulsion fxs (Segond sign - lateral tibial condyle avulsion fx)
      • osteochondral defects
  • MRI 
    • required to evaluate soft tissue injury (ligaments, meniscus) and for surgical planning 
    • obtain MRI after acute treatment
  • Initial Treatment
    • reduce knee and re-examine vascular status
      • considered an orthopedic emergency
      • splint in 20-30° flexion 
      • confirm reduction is held with repeat radiographs in brace/splint
      • vascular consult indicated if
        • if arterial injury confirmed by arterial duplex ultrasound or CT angiography
        • pulses are absent or diminished following reduction
  • Nonoperative
    • indications
      • limited and most cases require surgical stabilization
  • Operative
    • emergent surgical intervention with external fixation
      • indications
        • vascular repair (takes precedence)
        • open fx and open dislocation
        • irreducible dislocation
        • compartment syndrome
        • obese
        • multi trauma patient
      • technique
        • vascular intervention 
          • perform external fixation first
          • excision of damaged segment and repair with reverse saphenous vein graft
          • always perform fasciotomies after vascular repair
    • delayed ligamentous reconstruction/repair post
      • indications
        • generally instability will require some kind of ligamentous repair or fixation
        • patients can be placed in a knee immobilizer for 6 weeks for initial stabilization
          • improved outcomes with early treatment (within 3 weeks) 
      • technique
        • PLC
          • early reconstruction before ACL reconstruction
        • postoperative
          • recommend early mobilization and functional bracing
  • Stiffness (arthrofibrosis)
    • is most common complication (38%)
    • more common with delayed mobilization
  • Laxity and instability (37%)
  • Peroneal nerve injury (25%)
    • most common in posterolateral dislocations
    • poor results with acute, subacute, and delayed (>3 months) nerve exploration
    • neurolysis and tendon transfers are the mainstay of treatment
    • Dynamic tendon transfer involves transferring the posterior tibial tendon (PTT) to the lateral cuneiform. 
  • Vascular compromise
    • in addition to vessel damage, claudication, skin changes, and muscle atrophy can occur

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