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