Abstract

Total hip replacement is a widespread medical procedure, with over 300,000 surgeries performed each year in the US alone. The vast majority of total hip replacements utilize press fit fixation, where the implant cup is physically impacted into the patient's acetabular cavity. Successful seating of the implant requires a delicate balance between inserting the implant deep enough to obtain sufficient primary stability, while avoiding fracture of bone, which causes pain, complications during recovery, and revision surgery. To improve patient outcomes, this surgical field needs assistive technologies that can measure the forces applied during press fit fixation, and provide real-time feedback to guide how much force to apply, and when to stop applying additional forces. The development of such technology, however, requires a greater understanding of the forces experienced at the implant-acetabular cup interface, and the resulting cup insertion and implant stability. Here, we present a preliminary study of acetabular cup insertion into bone proxy samples. We find that as the magnitude of force on the acetabular cup increases, the cup displacement and axial extraction force increase linearly, then plateau. For repeated impacts of a given force, cup insertion and force experienced in bone increase correspondingly and reach a plateaued value over certain number of impacts, which represents rate of insertion. These finding suggest the plausibility of a feedback mechanism that utilizes measured force patterns in bone, implant/bone interface, and impaction tool in relation to rate of insertion to infer optimal primary implant stability in arthroplasty.

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