Knee Dislocation

Basics

Description

  • Defined by the position of the tibia in relation to the distal femur:
    • Anterior dislocation:
      • Most common
      • Hyperextension mechanism
      • Disruption of the posterior capsule, posterior cruciate ligament (PCL), and often the anterior cruciate ligament (ACL)
    • Posterior dislocation:
      • Second most common
      • Direct blow to the anterior tibia with the knee flexed at 90 degrees, “dashboard injury”
    • Medial dislocation:
      • Varus stress causing tear to the ACL, PCL, and lateral collateral ligament (LCL)
    • Lateral dislocation:
      • Valgus stress causing tear to the ACL, PCL, and medial collateral ligament (MCL)
      • Rotatory
      • PCL remains intact as the tibia rotates around the femur
  • Associated injuries:
    • Popliteal artery injury:
      • Associated with up to 40% of dislocations
      • High rates of arterial disruption due to anatomic tethering, proximally and distally
      • Disruption leads to intimal tears or transection and often delayed thrombosis
      • Very high rate of limb loss if vascular repair is delayed >8 hr
    • Peroneal nerve injury:
      • Associated with 25% of dislocations
      • Tethered proximally and distally to fibular neck
      • Injury due to traction or transection, most often with medial or rotatory dislocations
      • Permanent footdrop in >50% of patients, partial recovery another 25%

Etiology

  • High energy:
    • Fall from height, motor vehicle crashes, and auto vs. pedestrian accidents
  • Low energy:
    • Athletic injury (most often football), trampoline fall
  • Ultra-low energy:
    • Obese individuals
    • Routine walking

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