Intraprosthetic Dislocation Following Dual Mobility Total Hip Arthroplasty: A Retrieval Analysis Study.

Background: Dual mobility (DM) implants in total hip arthroplasty provide excellent range of motion with low dislocation rates. A complication of this design is intraprosthetic dislocation (IPD), where the polyethylene (PE) liner dissociates from the femoral head. In older designs, IPD occurred due to a small head size and late PE wear with head-capture-mechanism failure. Routine retrieval analysis identified concerns regarding IPD of modern implants, and scant reporting in the literature led to this retrospective study.

Methods: A total of 124 (110 primary, 14 revision) DM implants (mean in situ time 2.0 ± 3.1 years) revised by 20 surgeons across Western Australia between July 2014 and August 2023 were assessed. Demographics, clinical information, mechanisms of failure, and observations at revision arthroplasty were analyzed. The retrieval analysis included an assessment of metal and PE wear mechanisms, corrosion between modular components, and extent of bony attachment to acetabular shells.

Results: There were 11 cases of IPD. Of these, 8 (73%) had a documented preceding failed closed reduction, with the remaining 3 revised due to trunnionosis, loosening, and joint instability. Nine out of 11 (82%) cases were female. Although metallic wear and inner-lip impingement of PE bearings were observed, there was no obvious failure mechanism for the other 3 retrieved IPD implants.

Conclusions: Most cases of IPD in DM implants occur after failed closed reduction in the setting of a hip dislocation, suggesting an iatrogenic cause of IPD. No implant-related features could be defined for the remaining cases. Recognizing common failure modes can help with the prevention and treatment of this complication.