Knee

Question 1

What is the mechanism for knee dislocation?

Answer 1

• High energy
  
  • trauma/RTA
  • commonly dashboard injury- axial load to flexed knee
• Low energy
  
  • often althetic injury
  • generally has a rotational component
  • morbid obesity is a risk factor
• Assoc w significant soft tissue disruption
• 3/4 of ligaments disrupted

Question 2

What is the associated injuries with knee dislocation?

Answer 2

• Vascular injury
  
  • 5-15% all dislocations
  • 40-50% anterior/posterior dislocations
  • due to tethering at the popliteal fossa
    
    • proximal- fibrous tunnel at the adductor hiatus
    • distal - fibrous tunnel at soleus muscle
• Nerve Injury
  
  • Usually common peroneal nerve injury 25%
  • tibial n less common
• Fractures
  
  • present in 60%
  • tibia/femur common

Question 3

What is the classification of knee dislocations?

Answer 3

• On direction of displacement
  
  • Anterior
    
    • most common 30-50%
    • hyperextension injury
    • tears PCL
    • arterial injury = Intimal tear
  • Posterior
    
    • 2nd most common 25%
    • due to axial load to flexed knee = dashboard
    • highest rate of Complete tear of Popliteal A
  • ​Lateral
    
    • ​13% knee dislocations
    • due to varus/valgus force
    • usually tears ACL/PCL
    • Highest rate of peroneal n injury
  • ​Medial
    
    • ​Varus/ valgus force
    • usually PLC & PCL
  • Rotational
    
    • posterolateral most common
    • usually irreducible