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Knee Dislocation

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Topic updated on 04/01/16 1:58pm
Introduction
  • 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
Classification
  • Descriptive
    • based on direction of displacement of the tibia post
      • anterior
        • most common type of dislocation (30-50%)
        • due to hyperextension injury
        • usually involves tear of PCL
        • arterial injury is generally an intimal tear due to traction
      • posterior
        • 2nd most common type (25%)
        • due to axial load to flexed knee (dashboard injury)
        • highest rate of complete tear of popliteal artery
      • lateral
        • 13% of knee dislocations
        • due to varus or valgus force
        • usually involves tears of both ACL and PCL
        • highest rate of peroneal nerve injury
      • medial
        • varus or valgus force
        • usually disrupted PLC and PCL
      • rotational
        • posterolateral is most common rotational dislocation
        • usually irreducible
  • Schenck Classification
    • based on pattern of multiligamentous injury of knee dislocation (KD)
Schenck Classification
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)
KD IV Injury to ACL, PCL, PMC, and PLC (4 ligaments)
KD V Multiligamentous injury with periarticular fracture
 
Presentation
  • 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
        • do not wait for radiographs, 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
Imaging
  • 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
Treatment
  • Initial Treatment
    • reduce knee and re-examine vascular status
      • considered an orthopedic emergency
      • splint knee in 20-30 degrees of 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
      • indications
        • vascular injury repair (takes precedence)
        • open fx and open dislocation
        • irreducible dislocation
        • compartment syndrome
      • 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
          • recommend early reconstitution
        • PCL 
          • reconstruct prior to ACL reconstruction
        • postoperative
          • recommend early mobilization and functional bracing
Complications
  • 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
  • Vascular compromise
    • in addition to vessel damage, claudication, skin changes, and muscle atrophy can occur

 

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Qbank (5 Questions)

TAG
(SBQ12.5) Figures A and B are radiographs of a 20-year old male athlete that sustained a high impact tackle during a football game. What percentage of these injuries will present with an associated vascular injury? Topic Review Topic
FIGURES: A   B        

1. 10%
2. 20%
3. 40%
4. 70%
5. 90%

PREFERRED RESPONSE ▶
TAG
(OBQ13.128) A 30-year-old man is the front seat passenger in a motor vehicle accident. He presents with deformity in his knee seen in Figures A and B. Radiographs are seen in Figures C and D. Examination reveals weak foot pulses. After unsuccessful attempts at closed reduction, it is noted that the pulses are no longer palpable and the foot is cool. What is the next step in treatment? Topic Review Topic
FIGURES: A   B   C   D    

1. Open reduction through an anteromedial approach, spanning external fixation. If pulses do not return, perform popliteal artery exploration.
2. Closed reduction in the operating room using a femoral distractor. If pulses do not return, perform on-table angiogram.
3. Manual in-line skeletal traction using a calcaneal pin in the emergency room, provisional long-leg splinting. If pulses do not return, perform computed tomography angiography in the radiology suite.
4. Manual in-line skeletal traction using a proximal tibial pin in the emergency room, provisional long-leg splinting. If pulses do not return, perform standard angiography in the angiography suite.
5. Open reduction through a posterior approach, spanning external fixation. If pulses do not return, perform popliteal artery exploration.

PREFERRED RESPONSE ▶
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