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 recent literature suggests a significantly higher risk of neurovascular injury in morbidly obese patients 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