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Updated: Dec 24 2023

THA Dislocation

  • summary
    • THA Dislocation is a complication following THA and may occur due to patient noncomplicance with post-operative restrictions, implant malposition, or soft-tissue deficiency.
    • Diagnosis can be made with plain radiographs of the hip. CT of the pelvis can assist with assessing for implant malpositioning.
    • Treatment is closed reduction of the hip. Surgical management with possible revision THA is indicated for irreducible dislocations, recurrent instability, and implant malposition.
  • Epidemiology
    • Incidence
      • 1-3%
      • 70% occur within first month
      • 75-90% posterior
  • Etiology
    • Mechanism
      • anterior
        • extension and external rotation of hip
      • posterior
        • flexion, internal rotation, adduction of hip
      • prior hip surgery (greatest risk factor)
      • conflicting evidence regarding patient gender
      • higher comorbidity burden
      • BMI < 20 or > 35
      • use of meta-on-poly or metal-on-metal bearing surfaces
      • use of cemented components
      • 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
      • prior spinal fusion or fixed spinopelvic alignment
      • polyethylene wear
        • common cause of late instability occuring >5 years after procedure
  • 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
        • cross-table lateral
      • findings
        • increased acetabular inclination > 60°
        • increased acetabular anteversion > 20°
        • aceabular retroversion
        • look for eccentric position of femoral head as an indication of polyethylene wear and risk for impending dislocation
    • CT scan
      • indications
        • to assess for implant malposition 
  • 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 component
              • acetabular retroversion
            • implant failure
          • techniques
            • see below
      • 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
  • Technique
    • 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
        • utilization of a lateralized liner
          • increases femoral offset
        • 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
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