Early Intraprosthetic Dislocation of a Dual Mobility Acetabular Construct after Total Hip Arthroplasty

The concept of a dual mobility (DM) cup has been in existence for more than 40 years and was initially popularized in Europe. Only recently has it started to garner attention in the United States. Its design, consisting of a small femoral head articulating within a larger polyethylene (PE) insert, which articulates with an outer shell, has found increasing use in patients that are at risk for post-operative dislocations. This case report describes a case of recurrent total hip arthroplasty (THA) dislocation managed with the implantation of a DM cup with an acute intraprosthetic dislocation of the DM construct.

A 52-year-old woman underwent an uneventful left THA through a posterior approach. Within 6 weeks of her surgery, she had four dislocations, managed with closed reductions. She then underwent an open revision of her acetabular component with conversion to a DM construct. 5 weeks after her revision, she had another dislocation treated with closed reduction in the operating room, with the resultant eccentric location of the femoral head in the acetabular component. Computed tomography (CT) confirmed intraprosthetic dislocation with the PE liner lodged in the gluteal tissue. She was taken to the operating room with a plan to revise her acetabular component to another DM construct, but with an increase in the anteversion despite initial anteversion being "appropriate" on CT imaging. Intraoperatively, the PE liner was embedded in gluteal tissue as depicted on the CT. The abductors were intact. There was no impingement in extension and maximal external rotation when trialed with a conventional head/liner construct. A new DM construct was then implanted.

Intraprosthetic dislocation is a rare occurrence and unique complication to DM constructs. It is not common in the short-term setting postoperatively to our knowledge, and this case report represents an early report of intraprosthetic dislocation in the literature. Care should be taken during reduction of dislocated DM constructs to avoid intraprosthetic dislocations. Open revisions can be managed with revisions to another DM construct or to a constrained liner construct to maximize stability.