Hip Replacement Dislocation

Introduction

  • Dislocation following THA is a common reason for revision
  • Epidemiology
    • incidence 1-3%
    • 70% occur within first month
    • 75-90% posterior
  • Mechanism
    • anterior
      • extension and external rotation of hip
    • posterior
      • flexion, internal rotation, adduction of hip
  • Risk factors
    • prior hip surgery (greatest risk factor)
    • female sex
    • >70-80 years of age
    • posterior surgical approach
      • repairing capsule and reconstructing external rotators brings dislocation rate close to anterior approach
    • malpositioning of components
      • ideal positioning of acetabular component is 40 degrees of abduction and 15 degrees anteversion
      • in general, excessive anteversion increases risk of anterior hip dislocation; excessive retroversion increases risk of posterior hip dislocation
    • spastic or neuromuscular disease (Parkinson’s)
    • drug or alcohol abuse
    • decreased femoral offset (decreases tissue tension and stability)
    • decreased femoral head to neck ratio

Presentation

  • History
    • often reports activity that puts patient in a position that provokes dislocation (hip flexion, adduction, internal rotation)
      • shoe tying
      • sitting in low seat or toilet

Imaging

  • Radiographs
    • recommended views
      • AP pelvis, AP and true lateral of hip
    • findings
      • look for eccentric position of femoral head as an indication of polyethylene wear and risk for impending dislocation

Treatment

Nonoperative

  • closed reduction and immobilization
    • indications
      • two-thirds of early dislocations can be treated with closed reduction and immobilization
    • technique

immobilize with hip spica cast, hip abduction brace, or knee immobilizer

Operative

  • polyethylene exchange
    • indications
      • stable well-aligned implants with extensive polyethylene wear thought to be sole reason for dislocation
  • revision THA 
    • indications
      • indicated if 2 or more dislocations with evidence of
        • implant malalignment
          • vertical acetabular componen
          • acetabular retroversion
        • implant failure
        • polyethylene wear
  • conversion to hemiarthroplasty with larger femoral head
    • indications
      • for soft tissue deficiency or dysfunction
      • contraindicated if acetabular bone is compromised
      • older technique rarely used with development of dual mobility implants
  • resection arthroplasty
    • indications
      • when all options have been exhausted
      • significant bone loss and soft tissue deficiency
      • psychiatric patients who are dislocating for secondary gain

Techniques

  • Revision THA
    • techniques to prevent future dislocation during THA include
      • realign components
        • indicated if malalignment explains dislocation
          • retroverted acetabulum
          • vertical acetabulum
          • short femoral neck
          • lack of femoral neck offset
          • retroverted femoral component
      • head enlargement
        • optimize head-neck ratio
      • trochanteric osteotomy and advancement
        • places abductor complex under tension which increases hip compression force
      • conversion to a constrained acetabular component
        • indications
          • recurrent instability with a well positioned acetabular component due to soft tissue deficiency or dysfunction
      • conversion to dual mobility implant
      • conversion to tripolar construct
    • Adapted with permission from https://orthobullets.com