Development of a hip joint mathematical model to assess implanted and non-implanted hips under various conditions.

While total hip arthroplasty does generally improve patient quality of life, current systems can still yield atypical forces, premature component wear, and abnormal kinematics compared to native joints. Specifically, common complications include instability, separation, sliding, and edge loading within the hip joint. Unfortunately, evaluating potential solutions to these issues can be costly and time-consuming. Fortunately, mathematical modeling is an accurate and efficient tool that can be used to evaluate potential solutions. A forward dynamics mathematical model of the hip allows users to virtually insert a hip implant into a theoretical patient and observe the predicted postoperative mechanics. The objective of this study is therefore to develop, validate, and use a fully functional forward solution mathematical model that allows for a comparison between various hip implant designs and a determination of factors leading to in vivo hip separation, instability, and edge loading. The model presented herein has been validated kinetically against telemetric data and kinematically against fluoroscopic data. It was determined through this research that shifting of the joint rotation center during total hip arthroplasty has the potential to yield postoperative instability, and surgical errors can exacerbate these outcomes. However, the relationships between subject-specific joint shifting and hip instability are extremely complex, and therefore it becomes essential for surgeons to focus on implanting components as accurately as possible to minimize these risks.