منو منو

Knee Dislocation


  • SUMMARY

    • Knee dislocations are high energy traumatic injuries characterized by a high rate of neurovascular injury.

    • Diagnosis is made clinically with careful assessment of limb neurovascular status. Radiographs should be obtained to document reduction. 

    • Treatment is generally emergent reduction and stabilization with assessment of limb perfusion followed by delayed ligamentous reconstruction. 

  • EPIDEMIOLOGY

    • Incidence

      • rare

        • 0.02% of orthopedic injuries

        • likely underreported as approximately 50% self-reduce and are misdiagnosed

    • Demographics

      • 4:1 male to female ratio

    • Location

      • tibiofemoral articulation (knee joint)

    • Risk factors

      • morbid obesity is a risk factor for "ultra-low energy" knee dislocations with activities of daily living

  • PATHOPHYSIOLOGY

    • Mechanism of injury

      • high-energy vs low energy

        • high energy is usually from MVC, crush injury, fall from a height, or dashboard injury resulting in axial load to a flexed knee

        • low energy may be from an athletic injury or routine walking

      • hyperextension injury leads to anterior dislocations

      • posteriorly directed force across the proximal tibia (dashboard injuries) leads to posterior dislocations

    • Associated injuries

      • vascular injury

      • nerve injury

        • usually common peroneal nerve injury (25% incidence) 

           

        • tibial nerve injury is less common

      • fractures

        • present in 60% of dislocations

      • soft tissue injuries

        • patellar tendon rupture

        • periarticular avulsion

        • displaced menisci

  • ANATOMY

    • Osteology

      • the knee is a ginglymoid joint and consists of tibiofemoral, patellofemoral and tibiofibular articulations

    • Ligaments

      • PCL, ACL, LCL, MCL, and PLC are all at risk for injury

      • main stabilizers of the knee given the limited stability afforded by the bony articulations

    • Blood supply

      • popliteal artery injuries occur often due to tethering at the popliteal fossa

        • proximal - fibrous tunnel at the adductor hiatus

        • distal - fibrous tunnel at soleus muscle

      • geniculate arteries may provide collateral flow and palpable pulses masking a limb-threatening vascular injury

    • Biomechanics

      • the normal range of motion of 0-140 degrees with 8-12 degrees of rotation during flexion/extension

  • CLASSIFICATION

    • Descriptive

      • Kennedy classification based on the direction of displacement of the tibia

      • Kennedy classification 

        (based on the direction of displacement of the tibia)

      • Anterior (30-50%) 

      • most common

        due to hyperextension injury

      •  usually involves tear of PCL

      •  an arterial injury is generally an intimal tear due to traction

      • the highest rate of peroneal nerve injury

      •  
      •  
      • Posterior (30-40%)

      •  2nd most common

      •  due to axial load to the flexed knee (dashboard injury)

      • the highest rate of vascular injury based on Kennedy classification

         has highest incidence of a complete tear of the popliteal artery

         

      •  
      •  
      • Lateral (13%)

      •  due to a varus or valgus force

      •  usually involves tears of both ACL and PCL

      •  
      • Medial (3%)

      •  varus or valgus force

      •  usually disrupted PLC and PCL
      •  
      • Rotational (4%)

      •  usually irreducible

      •  posterolateral is most common rotational dislocation

      •  buttonholing of femoral condyle through the capsule
      •  
    • Schenck Classification

      • based on a pattern of multiligamentous injury of knee dislocation (KD)

      • Schenck Classification

        (based on the number of ruptured ligaments)

      •  
      • KD I

      • Multiligamentous injury with the involvement of the 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).

      •  
      • KD IV

      • Injury to ACL, PCL, PMC, and PLC (4 ligaments)

        Has the highest rate of vascular injury (5-15%%) 

      •  
      • 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

          • may present with subtle signs of trauma (swelling, effusion, abrasions, ecchymosis)

        • obvious deformity

          • reduce immediately, especially if absent pulses

          • "dimple sign" - buttonholing of medial femoral condyle through the medial capsule 

              

            • indicative of an irreducible posterolateral dislocation

            • a contraindication to closed reduction due to risks of skin necrosis 

               

      • 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 on injured and contralateral side

        • if pulses are present and normal

          • does not indicate the absence of arterial injury

            • collateral circulation can mask a complete popliteal artery occlusion

          • measure Ankle-Brachial Index (ABI) on all patients with suspected KD 

             

            • if ABI >0.9 

               

              • then monitor with serial examination (100% Negative Predictive Value)

            • if ABI <0.9

              • perform an 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%

          • imaging contraindicated if it will delay surgical revascularization

          • if pulses present after reduction then measure ABI then consider observation vs. angiography

      • neurologic exam

        • assess sensory and motor function of peroneal and tibial nerve as nerve deficits often occur concomitantly with vascular injuries

      • stability

        • diagnosis based on instability on physical exam (radiographs and gross appearance may be normal)

        • may see recurvatum when held in extension 

        • assess ACL, PCL, MCL, LCL, and PLC

  • IMAGING

    • Radiographs

      • recommended views

        • pre-reduction AP and lateral of the knee 

          • 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

        • post reduction AP and lateral of the knee

      • optional views

        • 45-degree oblique if fracture suspected

    • CT

      • indications

        • fracture identified on post reduction plain films

        • obtain post reduction CT for characterization of fracture

      • findings

        • tibial eminence, tibial tubercle, and tibial plateau fractures may be seen

    • MRI

      • indications

        • obtain MRI after acute reduction but prior to hardware placement

        • required to evaluate soft tissue injury (ligaments, meniscus) and for surgical planning 

  • TREATMENT

    • Nonoperative

      • emergent closed reduction followed by vascular assessment/consult

        • indications

          • considered an orthopedic emergency

        • vascular consult indicated if

          • pulses are absent or diminished following reduction

          • if arterial injury confirmed by arterial duplex ultrasound or CT angiography

      • immobilization as definitive management

        • indications (rare)

          • successful closed reduction without vacular compromise

          • most cases require some form of surgical stabilization following reduction

        • outcomes

          • worse outcomes are seen with nonoperative management

          • prolonged immobilization will lead to loss of ROM with persistent instability

    • Operative

      • open reduction

        • indications

          • irreducible knee

          • posterolateral dislocation

          • open fracture-dislocation

          • obesity (may be difficult to obtain closed)

          • vascular injury

      • external fixation

        • indications

          • vascular repair (takes precedence)

          • open fracture-dislocation

          • compartment syndrome

          • obese (if difficult to maintain reduction)

          • polytrauma patient

      • delayed ligamentous reconstruction/repair

        • indications

          • instability will require some kind of ligamentous repair or fixation

          • patients can be placed in a knee immobilizer until treated operatively

            • improved outcomes with early treatment (within 3 weeks)

  • TECHNIQUE

    • Closed reduction

      • approach

        • anterior dislocation - traction and anterior translation of the femur

        • posterior dislocation - traction, extension, and anterior translation of the tibia

        • medial/lateral - traction and medial or lateral translation

        • rotatory - axial limb traction and rotation in the opposite direction of deformity

      • splinting

        • 20 to 30 degrees of flexion

    • Open reduction

      • approach

        • midline incision with a medial parapatellar arthrotomy

      • soft tissue

        • the medial capsule may need to be pulled over medial condyle if buttonholed

        • acute associated soft tissue injuries (patellar tendon rupture, periarticular avulsion, or displaced menisci) may benefit from acute repair

      • bone work

        • periarticular fractures may be fixed acutely or spanned with external fixator depending on surgeon preference

      • instrumentation

        • place knee-spanning external fixator in 20-30 degrees of flexion with knee reduced in AP and sagittal planes

    • Early ligamentous reconstruction (<3 weeks)

      • approach

        • arthroscopic versus open

          • arthroscopic may not be possible if large capsular injury and creates a risk of fluid extravasation and compartment syndrome

          • PLC and PMC require open reconstruction given subcutaneous nature and proximity to neurovascular structures

      • soft tissue work

        • arthroscopic reconstruction of ACL and/or PCL

        • address intraarticular pathology (menisci, cartilage defects, capsular injury)

        • open repair versus reconstruction of collateral ligaments

      • outcomes 

         

        • recent systematic review suggests that patients who undergo staged reconstruction have a higher likelihood of having good to excellent outcomes

        • acute (< 3 weeks) reconstruction is associated with a higher incidence of residual instability and stiffness that is resistant to nonoperative interventions

  • COMPLICATIONS

    • Vascular compromise

      • incidence

        • 5-15% in all dislocations

        • 40-50% in anterior or posterior dislocations 

           

      • risk factors

        • KD IV injuries have the highest rate of vascular injuries

      • treatment

        • emergent vascular repair and prophylactic fasciotomies

    • Stiffness (arthrofibrosis)

      • incidence

        • most common complication (38%) 

           

      • risk factors

        • more common with delayed mobilization

      • treatment

        • avoid stiffness with early motion

        • arthroscopic lysis of adhesion

        • manipulation under anesthesia

    • Laxity and instability

      • incidence

        • 37% of some instability, however, redislocation is uncommon

      • treatment

        • bracing

        • revision reconstruction

    • Peroneal nerve injury

      • incidence

        • 25% occurrence of a peroneal nerve injury

        • 50% recover partially

      • risk factors

        • male gender

        • increased BMI

        • associated fibular head fracture

      • treatment 

        • AFO to prevent equinus contracture

        • neurolysis or exploration at the time of reconstruction

        • nerve repair or reconstruction or tendon transfers if chronic nerve palsy persists

        • dynamic tendon transfer involves transferring the posterior tibial tendon (PTT) to the foot 

           

  • PROGNOSIS

    • Complications frequent and rarely does knee return to a pre-injury state

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