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 Risk factors 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 login to view 1 more bullet technique login to view 1 more bullet Operative polyethylene exchange indications login to view 1 more bullet revision THA indications login to view 8 more bullets conversion to hemiarthroplasty with larger femoral head indications login to view 3 more bullets resection arthroplasty indications login to view 3 more bullets Technique Revision THA techniques to prevent future dislocation during THA include realign components login to view 6 more bullets head enlargement login to view 1 more bullet utilization of a lateralized liner login to view 1 more bullet trochanteric osteotomy and advancement login to view 1 more bullet conversion to a constrained acetabular component login to view 2 more bullets conversion to dual mobility (DM) implant login to view 3 more bullets conversion to tripolar construct