Intraprosthetic dislocation of a contemporary dual-mobility design used during conversion THA.

Although dual-mobility sockets have been in clinical use for decades in other parts of the world, they recently gained popularity in the United States as an option for primary and revision total hip arthroplasty (THA). Improvements in dual-mobility socket technology include articulation with a metal insert impacted into a metal shell and a femoral head made of highly cross-linked polyethylene. The results and complications associated with the use of dual-mobility sockets employing these technologic advancements are not known. Specifically, intraprosthetic dislocation is a well-known complication of these implants and has been reported extensively in the literature. To the authors' knowledge, its occurrence in a modern dual-mobility socket has not been reported. The authors report a case of early intraprosthetic dislocation of a contemporary dual-mobility design used to convert a patient to THA after failed fixation of intertrochanteric hip fracture. At retrieval, there was evidence that the outer bearing may have ceased moving, causing localized focal impingement of the implant neck on the retentive ring. The authors theorized that external hip impingement (pelvic against trochanter) and previous surgery that led to the formation of scar tissue could have caused the outer bearing surface to cease its motion. This ultimately led to impingement of the femoral component neck on the retentive ring, which led to the intraprosthetic dislocation. Dual-mobility cups provide an attractive option to decrease wear and improve stability. Further research is needed to establish the ideal construct design and materials.