Dislocation of bipolar hemiarthroplasty: rate, contributing factors, and outcome.

UNLABELLED: Dislocation of bipolar hemiarthroplasty of the hip is a rare complication. The objectives of our study were to assess the incidence, contributing factors, and outcomes of bipolar prosthesis dislocation. From 1974 to 2001, 1812 primary bipolar hemiarthroplasties were done at our institution. Seventy-four percent were done in patients with fractures of the femoral neck. An anterolateral surgical approach was used in 79% of hips, a posterolateral approach was used in 14% of hips, and a transtrochanteric approach was used in 7% of hips. Thirty-two hips dislocated. The cumulative probabilities of dislocation at 1 year, 5 years, 10 years, and 20 years were 1.1% (95% CI range, 0.6%-1.6%), 1.5% (95% CI range, 0.9%-2.1%), 2.1% (95% CI range, 1.2%-3.1%), and 5% (95% CI range, 1.9%-9.6%), respectively. There was no significant association of dislocation with the surgical approach or with the primary operative diagnosis. More than (1/2) of the dislocations occurred within 6 months postoperative. Late dislocations occurred most commonly in patients with Bateman prostheses and osteonecrosis and were associated with inner bearing dissociation. Closed reduction was successful in preventing additional surgery in only 30% of patients. The surgeon must be aware that closed reduction may be unsuccessful, and open reduction with replacement of components may be necessary. LEVEL OF EVIDENCE: Therapeutic study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.