Acute Disassembly and Dissociation of a Dual-Mobility Next-Generation Prosthesis

The use of bipolar components in hip surgery was introduced more than 40 years ago with the rationale of a dual-mobility hip implant. This design used a small femoral head that would decrease the rate of wear because of the smaller surface area but would still provide implant stability because of the larger outer shell that articulated with the acetabulum, decreasing dislocation rates. In April 2011, the E1 Active Articulation Hip System (Biomet, Warsaw, Indiana) was introduced to the orthopedic market. It is considered to be part of the next generation of bipolar designs, with similar designs available from competing companies, such as Stryker (Mahwah, New Jersey). These designs merge the concept of an articulating outer shell with an all-polyethylene spacer with the primary articulation of a ceramic head and an outer polyethylene shell spacer. This case report describes disassembly and dissociation at the site of the primary articulation of a bipolar system that occurred between the ceramic femoral head and the outer all-polyethylene articulating shell in a patient who had revision total hip arthroplasty because of metallosis. The patient had a stable nonpainful metal-on-metal arthroplasty at first, immediately after the initial procedure. Although previous intraprosthetic dislocations (also called retentive failures) have occurred, this case has several unique features. [Orthopedics.2016; 39(5):e980-e983.].