Hip Arthroplasty Safe Zone: Questioning Historic Assumptions

HCPLive—October 8, 2014

Nearly one in 10 patients who undergo total hip arthroplasty (THA) experience post-operative dislocation. Many factors can contribute to dislocation: previous studies have identified use of a smaller femoral head and a posterolateral surgical approach as increasing dislocation risk. Since 1978, orthopedic surgeons have used the Lewinnek safe zone as a guide for the best position for acetabular components to reduce dislocation risk. Lewinnek et al. defined this zone based on a very small sample size, and some surgeons have questioned its validity.

Researchers from the Hospital for Special Surgery, New York, have published a study indicating that component position alone is not protective against instability.

This study used a large prospective institutional registry to reexamine the question of a safe zone for acetabular component position. They identified patients who experienced a dislocation event within six months after hip arthroplasty surgery. Among the 7,040 patients who underwent this procedure, 2.1% (147) experienced dislocation; this rate is within expected limits. The researchers employed anteroposterior radiographs to measure acetabular component position.

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