A unique failure mechanism of a constrained total hip arthroplasty: a brief review of the literature.

Constrained acetabular systems are successful in achieving stability in patients with recurrent dislocations, abductor deficiency, or where a source of instability cannot be determined. We report on one patient with 2 dissociations of a tripolar constrained acetabular liner caused by impingement when the patient exceeded the allowed range of motion. The inner liner dissociated from the outer liner, whereas the reinforcing ring remained intact and in place. Despite an extensive literature search, we were unable to find any other published reports concerning this specific mode of failure for this constrained liner. Surgeons should be aware that constrained liners are not infallible and have limitations to range of motion. Maximizing the size of the femoral head may reduce the risk of this mode of failure.