knee dislocation

Question 1

Associated injuries

Answer 1

• 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
  • ligaments injuries

Question 2

Prognosis

Answer 2

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

Question 3

Classification

Answer 3

1. Kennedy classification
2. Schenck Classification

Question 4

Kennedy classification

Answer 4

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
• 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
  • 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
  • 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

Question 5

Schenck Classification

Answer 5

Schenck Classification

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

Question 6

vascular exam

Answer 6

• 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

Question 7

stability

Answer 7

• 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

Question 8

Radiographs

Answer 8

• 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

Question 9

Nonoperative

Answer 9

• 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

Question 10

Operative

Answer 10

• 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)

Question 11

Early ligamentous reconstruction (<3 weeks)

Answer 11

• 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

Question 12

Complications

Answer 12

1. Vascular compromise
2. Stiffness (arthrofibrosis)
3. Laxity and instability
4. Peroneal nerve injury

Question 13

Vascular compromise

Answer 13

• 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

Question 14

Stiffness (arthrofibrosis)

Answer 14

• incidence
  
  • 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

Question 15

Laxity and instability

Answer 15

• incidence
  
  • 37% of some instability, however, redislocation is uncommon
• treatment
  
  • arthroscopic lysis of adhesion
  • manipulation under anesthesia

Question 16

Peroneal nerve injury

Answer 16

• 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 foot