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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
  • 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
        • 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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