Impingement in total hip arthroplasty a study of retrieved acetabular components.

Impingement can damage the acetabular liner, create polyethylene wear, and cause dislocation. We determined the prevalence of impingement, its relation with dislocation, and the influence of patient, surgical, and design factors in 162 components randomly selected from a larger group retrieved between 1990 and 1999. Impingement arc, severity, and wear damage were measured; patient data were obtained from medical records, and component position was determined from radiographs. More than half (56%) showed impingement, including 94% of those removed for dislocation. The occurrence of impingement was significantly increased if the revision diagnosis was dislocation, if the component had a large outer diameter or an elevated rim, and if the femoral component had an extended flanged neck. Implant design, in particular head/neck ratio, can help reduce the prevalence of impingement.