This article presents a case of early intraprosthetic dislocation of a dual-mobility hip prosthesis after revision total hip arthroplasty for instability. A 70-year-old woman was revised to a dual-mobility cup for multiple hip dislocations. She dislocated the dual-mobility construct twice, which was closed reduced. Postreduction radiographs after the second closed reduction showed that the femoral head was eccentrically positioned within the acetabular shell, raising suspicion for intraprosthetic dislocation or disassociation between the femoral head and the mobile polyethylene liner. After closed reduction, the patient reported a mobile, golf ball-size mass deep to the posterior lateral incision and new onset of crepitus. Magnetic resonance imaging verified complete intraprosthetic dissociation between the femoral head and mobile polyethylene liner, which was located between the gluteus medius and minimus. The dual-mobility cup was revised to a constrained socket with retention of the femoral stem. The patient recovered uneventfully without further instability.
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