Failure of Cemented Constrained Acetabular Component at the Bipolar Outer Femoral Head Interface in Revision Hip Arthroplasty

Constrained acetabular components are used as a salvage option for unstable total hip arthroplasties particularly in elderly low demand patients. Their indications include multiple failed revisions with abductor deficiency, neurologic or neuromuscular impairment, recurrent dislocations where the cause of instability cannot be identified despite well-aligned components. Failure of these components occurred due to increased forces across the bone-component interface or failure of the locking mechanisms. We report a unique mode of failure of a constrained cup through dissociation of the outer femoral bipolar femoral head interface in all-poly cemented constrained components 5-years post implantation with a review of the relevant literature.