Updated: 10/22/2018

Knee Dislocation

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Introduction
  • Overview
    • Knee dislocations are traumatic injuries characterized by a high rate of vascular injury and seen in high and low energy injuries
      • treatment is generally emergent reduction and assessment of limb perfusion
  • Epidemiology
    • incidence
      • 0.02% of orthopedic injuries
      • likely underreported as approximately 50% self-reduce and misdiagnosed
    • demographics
      • 4:1 male to female ratio
    • location
      • tibiofemoral articulation
    • 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, routine walking, or morbidly obese ultra-low injury
      • 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%) 
      • tibial nerve injury is less common
    • fractures
      • present in 60% of dislocations
    • soft tissue injuries
      • patellar tendon rupture
      • periarticular avulsion
      • displaced menisci
  • Prognosis
    • complications frequent and rarely does knee return to a pre-injury state
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 post
      • 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
      • posterior (30-40%)
        • 2nd most common 
        • due to axial load to the flexed knee (dashboard injury)
        • the highest rate of vascular injury (25%) based on Kennedy classification
        • the highest rate 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
        • the highest rate of peroneal nerve injury
      • medial (3%)
        • varus or valgus force
        • usually disrupted PLC and PCL
      • rotational (4%)
        • posterolateral is most common rotational dislocation
        • usually irreducible
        • 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) KDIV has the highest rate of vascular injury (5-15%%) based on Schenck classification

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
  • 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 posterior 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
      • acute reconstruction (<3 weeks) has been shown to lead to improved clinical and functional outcomes
Complications
  • Vascular compromise
    • incidence
      • 5-15% in all dislocations
      • 40-50% in anterior and posterior dislocations 
    • risk factors
      • KD IV injuries have the highest rate of vascular injuries
    • treatment
      • emergent vascular repair and fasciotomies
  • Stiffness (arthrofibrosis)
    • incidence
      • is the most common complication (38%)
    • risk factors
      • more common with delayed mobilization
    • treatment
      • avoid stiffness with early reconstruction and motion
      • arthroscopic lysis of adhesion
      • manipulation under anesthesia
  • Laxity and instability 
    • incidence
      • 37% of some instability, however, redislocation is uncommon
    • treatment
      • arthroscopic lysis of adhesion
      • manipulation under anesthesia
  • Peroneal nerve injury 
    • incidence
      • 25% occurrence of a peroneal nerve injury
      • 50% recover partially
    • risk factors
      • posterolateral dislocations
    • 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 lateral cuneiform. 
 

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(OBQ13.128) A 30-year-old man is the front seat passenger in a motor vehicle accident. He presents with deformity in his knee seen in Figures A and B. Radiographs are seen in Figures C and D. Examination reveals weak foot pulses. After unsuccessful attempts at closed reduction, it is noted that the pulses are no longer palpable and the foot is cool. What is the next step in treatment? Review Topic

QID: 4763
FIGURES:
1

Open reduction through an anteromedial approach, spanning external fixation. If pulses do not return, perform popliteal artery exploration.

69%

(3313/4798)

2

Closed reduction in the operating room using a femoral distractor. If pulses do not return, perform on-table angiogram.

14%

(680/4798)

3

Manual in-line skeletal traction using a calcaneal pin in the emergency room, provisional long-leg splinting. If pulses do not return, perform computed tomography angiography in the radiology suite.

3%

(145/4798)

4

Manual in-line skeletal traction using a proximal tibial pin in the emergency room, provisional long-leg splinting. If pulses do not return, perform standard angiography in the angiography suite.

4%

(169/4798)

5

Open reduction through a posterior approach, spanning external fixation. If pulses do not return, perform popliteal artery exploration.

10%

(463/4798)

ML 3

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PREFERRED RESPONSE 1

(SBQ12TR.5) Figures A and B are radiographs of a 20-year old male athlete that sustained a high impact tackle during a football game. What percentage of these injuries will present with an associated vascular injury? Review Topic

QID: 3920
FIGURES:
1

10%

4%

(161/4265)

2

20%

17%

(709/4265)

3

40%

60%

(2552/4265)

4

70%

15%

(640/4265)

5

90%

4%

(186/4265)

ML 4

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PREFERRED RESPONSE 3
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