[Obturator externus impingement after total hip replacement].

A patient with a painful total hip replacement that is not obviously loose presents a diagnostic challenge. One of the rare causes is psoas impingement syndrome. Because there are several periarticular muscles, further muscle impingements are possible. We report on a case of painful obturator externus muscle impingement on the acetabular cup. On magnetic resonance imaging, a pathologic contact between the obturator externus muscle and the caudal rim of the cup was seen. A positive injection confirmed the pathologic contact.