Mechanisms of failure of total hip replacements: lessons learned from retrieval studies.

The value of implant retrieval analysis in orthopaedic surgery has been well recognized. Prosthetic devices retrieved for cause at revision surgery (for implant failure) or devices retrieved postmortem from patients with clinically successful reconstructions provide a unique set of specimens that can be studied to evaluate the effect of the implant on the host environment and the effect of the host environment on the implant. A systematic analysis of retrieved components, in combination with histologic, radiographic, and clinical data can provide valuable insights into the mechanisms of failure of the biomaterials used in joint replacement applications. From the hip implant retrieval studies reported to date, it has been established that the local reaction to particulate wear debris initiates the formation of a granulomatous tissue that ultimately invades the bone-implant interface and results in aseptic loosening. Cement mantle defects, noncircumferential porous coatings, and screw holes can serve as preferential access pathways for the progression of this granulomatous process yielding distinctive patterns of implant loosening and osteolysis. Continued surveillance of retrieved devices is strongly recommended to deepen our understanding of implant failure mechanisms and to evaluate the impact of newer designs and materials on the performance of joint replacement devices.