Considerations in the Design of Modular Neck Femoral Implants

Recent advances in modularity of total hip replacement offer the surgeon greater intraoperative flexibility to accurately reconstruct the hip joint. As was the case two decades ago with the introduction of modular heads, concerns regarding an additional potential site of implant fracture and particulate debris generation need to be addressed. The goal of this study was to identify key factors in the design, analysis and testing of modular neck implants related to these concerns.

The proximal strength of the implant was investigated under several different loading conditions. Iterations of design, finite element analysis and physical testing revealed that it is important to consider stress state as well as other factors. These factors influence fretting fatigue performance, which in turn affect the strength of the implant design. Various design parameters, including material selection, junction geometry and the amount of version, were found to significantly influence the ability to meet primary hip stem performance expectations. Specifically, the analysis of necks with anteversion and retroversion was critical. Small changes in implant design can profoundly influence the performance of the modular neck implant.

Finally, consideration was given to the neck/stem junction stability via distraction testing. The results demonstrated a distraction strength greater than that of traditional modular head/neck junctions.