Introduction

A knee dislocation is the disruption of the tibiofemoral articulation. An acute knee dislocation is an orthopaedic emergency that can result in severe consequences if untreated. Importantly, knee dislocations do not always present with obvious deformity, making it crucial that the evaluating physician remain clinically suspicious when evaluating patients with knee pain and be aware of proper treatment algorithms (▶Video 37.1).

I. Preoperative

1. 
   

   History and physical examination

   
   
   
   
   1. 
      

      Mechanism—high versus low energy:

      
      
      
      
      1. 
         

         High energy—motor vehicle accident, pedestrian hit by car, crush.

         
         
      2. 
         

         Low energy—athletic injury, misstep (usually with twisting fall), morbidly obese patient.

      
      
   2. 
      

      Appearance:

      
      
      
      
      1. 
         

         Obvious deformity:

         
         
         
         
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           i. Do not delay reduction for formal X-rays (XRs) if obvious deformity is present—reduce immediately.

           
           
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           ii. If irreducible via closed means, there may be interposition of medial tissue from the medial femoral condyle buttonholing through the medial capsule (▶ Fig. 37.1 ). This may require open reduction in the operating room.

           

         
         
      2. 
         

         No obvious deformity. Note that only subtle signs of trauma (swelling, bruising, abrasions) may present since roughly 50% of knee dislocations spontaneously reduce. One must have a high index of suspicion and perform a ligamentous examination for knee stability.

      
      
   3. 
      

      Vascular examination (▶ Fig. 37.2 )—a good vascular exam is crucial as up to 40 to 50% of knee dislocations can be associated with vascular injury. There is approximately an 85% amputation rate with greater than 8 hour interrupted blood flow.

      

      
      
      
      
      1. 
         

         Palpable pulse:

         
         
         
         
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           i. Dorsalis pedis and posterior tibial pulses should be checked immediately and compared to the uninjured limb.

           
           
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           ii. Pulses should be checked serially—pulse may be present initially in 5 to 15% of those with vascular injury (collateral circulation may initially mask injury) and then may decrease or become nonpalpable with time.

           
           
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           iii. Pulses should be documented before and after the reduction along with subsequent serial examination.

           
           
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           iv. If the pulse is not palpable, or unequal to the contralateral (uninjured) limb, use Doppler.

         
         
      2. 
         

         Ankle-brachial index (ABI):

         
         
         
         
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           i. ABI should be measured even if pulse is palpable.

           
           
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           ii. When ABI is greater than 0.9, vascular injury is unlikely (99–100% negative predictive value), continue to monitor with serial examinations.

           
           
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           iii. When ABI is less than 0.9, further testing is needed, like CT angiography or arterial duplex ultrasound (if patient cannot be given contrast). Consult vascular surgery if arterial injury is diagnosed.

      
      
   4. 
      

      Neurologic examination:

      
      
      
      
      1. 
         

         Neurologic examination is important for detecting nerve deficits and detecting vascular injury as nerve injury is significantly associated with vascular disruption.

         
         
      2. 
         

         The common peroneal nerve (CPN) is most commonly injured due to its superficial anatomical location traversing around the proximal fibula near the knee joint.

         
         
         
         
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           i. Injury occurs in up to 40% of knee dislocations.

           
           
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           ii. Sensory (numbness on dorsum of foot and/or dorsum of the first web space) and/or motor deficits (foot drop).

           
           
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           iii. Highly associated with injury to the posterolateral corner (PLC).

         
         
      3. 
         

         Tibial nerve is less likely to be injured due to its protected location and more consistent blood supply.

      
      
   5. 
      

      Examination of knee stability:

      
      
      
      
      1. 
         

         Cruciate ligaments:

         
         
         
         
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           i. Anterior cruciate ligament (ACL):

           
           
           
           
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             Test: Lachman’s test, anterior drawer test (▶ Fig. 37.3 ).

             

           
           
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           ii. Posterior cruciate ligament (PCL):

           
           
           
           
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             Test: posterior sag sign, posterior drawer test (▶ Fig. 37.4 ).

             

             
             
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             Dial test at 90 degrees (combined with PLC injury).

         
         
      2. 
         

         Collateral ligaments:

         
         
         
         
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           i. Medial collateral ligament (MCL):

           
           
           
           
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             Test—valgus stress at 30-degree flexion to isolate MCL (▶ Fig. 37.5 ).

             

             
             
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             Note—laxity to valgus stress at 0 degrees indicates likely presence of cruciate ligament injury in addition to MCL/posteromedial corner injury.

           
           
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           ii. Lateral collateral ligament (LCL):

           
           
           
           
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             Test—varus stress at 30-degree flexion isolates LCL (▶ Fig. 37.6 ).

             

             
             
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             Note—laxity to varus stress at 0 degrees indicates likely presence of cruciate ligament injury in addition to LCL/PLC injury.

         
         
      3. 
         

         PLC:

         
         
         
         
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           i. Composed of LCL, popliteus tendon, popliteofibular ligament, lateral capsule, biceps femoris, iliotibial band, and lateral head of gastrocnemius.

           
           
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           ii. Test—dial test:

           
           
           
           
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             Greater than 10 degrees increased external rotation of foot (when compared to contralateral uninjured limb) with knee in 30-degree flexion ONLY = PLC injury; PCL likely intact.

             
             
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             Greater than 10 degrees increased external rotation of foot with knee in 30- AND 90-degree flexion = PLC and PCL injury.

   
   
2. 
   

   Anatomy (▶ Fig. 37.7 ):

   

   
   
   
   
   1. 
      

      Disruption of the tibiofemoral articulation in any direction—involves damage to at least two ligaments of the knee, often more.

      
      
   2. 
      

      ACL—origin: lateral femoral condyle; insertion: anterior between intercondylar eminences of tibia.

      
      
   3. 
      

      PCL—origin: lateral edge of medial femoral condyle; insertion: tibial sulcus.

      
      
   4. 
      

      MCL—origin: proximal and posterior to medial epicondyle of femur; insertion: proximal: 1.2 cm distal to joint line; distal: medial surface of tibia 6 cm distal to joint line.

      
      
   5. 
      

      PLC:

      
      
      
      
      1. 
         

         LCL—origin: lateral epicondyle of femur; insertion: anterolateral fibular head.

         
         
      2. 
         

         Popliteus—origin: muscle originates posteromedial proximal tibia; insertion: tendon inserts lateral femoral condyle 18.5 mm distal and anterior to LCL femoral origin.

         
         
      3. 
         

         Popliteofibular ligament—origin: musculotendinous junction popliteus tendon; insertion: fibular head.

         
         
      4. 
         

         Arcuate ligament—origin: posterior portion of head of fibula; insertion: popliteus muscle and lateral epicondyle of femur.

         
         
      5. 
         

         Lateral capsule.

   
   
3. 
   

   Imaging

   
   
   
   
   1. 
      

      Radiographs:

      
      
      
      
      1. 
         

         Gross deformity on XR is obvious—immediate reduction should not be postponed for initial XRs.

         
         
      2. 
         

         Since approximately half of knee dislocations will present reduced, subtle signs of knee dislocation on XR should be noted:

         
         
         
         
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           i. Avulsion fractures:

           
           
           
           
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             Segond fracture (▶ Fig. 37.8 )—avulsion of the proximal, lateral tibia near joint line, which occurs due to avulsion of the anterolateral ligament off of the tibia. Considered a pathognomonic sign for ACL tear.

             

             
             
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             Arcuate fracture—avulsion fracture of the proximal fibula, which is significant for a PLC injury.

             
             
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             Rim fracture of the tibia.

           
           
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           ii. Osteochondral defects.

      
      
   2. 
      

      MRI:

      
      
      
      
      1. 
         

         Not necessary for acute evaluation.

         
         
      2. 
         

         Should be obtained after the patient is stabilized in order to fully evaluate ligamentous and meniscal injury and plan for future reconstruction.

   
   
4. 
   

   Classification

   
   
   
   
   1. 
      

      Three classification schemes:

      
      
      
      
      1. 
         

         Kennedy’s (anatomic) classification—based on the direction of tibial displacement but does not provide information on ligaments involved.

         
         
         
         
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           i. Anterior (most common).

           
           
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           ii. Posterior.

           
           
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           iii. Lateral.

           
           
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           iv. Medial.

           
           
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           v. Rotational.

           
           
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           vi. Anterior/posterior: 40 to 50% associated with vascular injury.

         
         
      2. 
         

         Schenck’s classification (▶ Table 37.1 )—based on ligamentous injury (grade III injuries) and allows description of neurologic or vascular injuries.

         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         
         

         Table 37.1 Schenck’s classification

         Type	Description
         KD I	Single cruciate (ACL or PCL) + 1 collateral
         KD II	Dual cruciate (ACL + PCL)
         KD III-M	ACL, PCL, and MCL injury
         KD III-L	ACL, PCL, and LCL + PCL injury
         KD IV	ACL, PCL, MCL, and LCL +PLC injury
         KD V	Dislocation + fracture
         	C = arterial injury; N = nerve injury
         Abbreviations: ACL, anterior cruciate ligament; KD, knee dislocation; LCL, lateral collateral ligament; MCL, medial collateral ligament; PCL, posterior cruciate ligament; PLC, posterolateral corner.