http://upload.orthobullets.com/topic/1043/images/Xray - Lat - knee dislocation (emedicine)_moved.jpg
http://upload.orthobullets.com/topic/1043/images/Clinical photo - recurvatum (emedicine)_moved.jpg
http://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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Questions (2)

(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? Review Topic


Open reduction through an anteromedial approach, spanning external fixation. If pulses do not return, perform popliteal artery exploration.




Closed reduction in the operating room using a femoral distractor. If pulses do not return, perform on-table angiogram.




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.




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.




Open reduction through a posterior approach, spanning external fixation. If pulses do not return, perform popliteal artery exploration.



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This patient has a posterolateral knee dislocation with a avascular limb. Urgent surgical intervention is warranted. The medial femoral condyle (MFC) has button-holed through the medial capsuloligamentous structures, leaving skin and medial subcutaneous tissues entrapped between the MFC and the joint cavity producing a ‘pucker sign’. An anteromedial approach is necessary. Stabilization is then best achieved with an external fixator. Persistent ischemia (absence of pulses after reduction) is an indication for popliteal artery exploration.

Posterolateral dislocations are caused by a posterior-directed and rotational force, and are often irreducible. Vascular injury arises because of proximal tethering (fibrous adductor hiatus tunnel) and distal tethering (fibrous soleus hiatus tunnel) at the popliteal fossa.

Rihn et al. outlined the treatment algorithm for acutely dislocated knees. If pulses return after reduction, radiographs and evaluation of ABI are indicated. If ABI<0.9, CT angiography or formal angiography is indicated. If ABI >0.9, a period of in-hospital observation is indicated. If pulses remain absent and the limb remains ischemic following reduction, emergent surgical exploration and revascularization in the operating room is necessary. The spanning external fixator supplies enough rigidity to maintain reduction and allows access for serial neurovascular examinations.

Patterson et al. examined knee dislocations with vascular injury in the Lower Extremity Assessment Project (LEAP) study. Of the 18 patients in this group, all required popliteal arterial repair. Overall, 14 patients were treated with limb salvage and 4 patients were treated with an amputation. Patients with salvaged limbs had moderate to high level of disability 2 years after injury.

Figures A and B show the clinical appearance of posterolateral knee dislocation with a ‘pucker sign’. Figures C and D are radiographs showing posterolateral knee dislocation. These radiographs classically show 1 view of the tibia, but another view of the femur. Thus, the AP XR shows an AP of the tibia, but an oblique of the femur. Similarly, the lateral XR shows a lateral of the tibia, and an oblique of the femur. This is because XR technologist determines the AP/lateral projection based on the position of the foot (which follows the tibia).

Incorrect Answers:
Answer 2: Closed reduction is contraindicated because of the risk of skin necrosis, and is also unlikely to be successful because of button-holing. While a femoral distractor is a useful tool to aid reduction, an external fixator is necessary to hold the reduction post-operatively.
Answers 3 and 4: While the limb may be splinted to aid transfer to the operating room, the next step must involve open reduction of the dislocated limb, which can only take place in the operating room. Skeletal traction is unlikely to be successful because of button-holing.
Answer 5: An anterior approach to the knee is necessary to free the entrapped structures.

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(SBQ12TR.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? Review Topic





















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Approximately 40% of low-velocity anterior knee dislocations are associated with popliteal vascular injury.

Anterior knee dislocations, which are the most common of all directional dislocations, are produced by a hyperextension mechanism. This causes the tibia to translate anterior to the femur and the popliteal vessels to stretch, causing intimal tears.

Wascher et al. reviewed the association of vascular injury with traumatic knee dislocations. They showed that 50% of all knee dislocations spontaneously reduce. However, patients who present with reduced knee dislocations have a similar risk of vascular injury (~ 40%) and other concurrent injuries as those who present with a dislocated knee.

Levy et al. reviewed the timing of treatment of multiligament-injured knee injuries arising from acute knee dislocations. They suggest that early operative treatment of the multiligament-injured knee yields improved functional and clinical outcomes compared with nonoperative management or delayed surgery. They noted that repair of the PLC, either acute or delayed, may yield higher revision rates compared with reconstruction options.

Figures A and B show AP and lateral radiographs of an anterior knee dislocation. A video is provided that gives a brief overview of knee dislocations.


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