Patient-Specific Component Alignment in Total Hip Arthroplasty

Abstract

Appropriate component alignment is critical for improving stability, maximising bearing performance and restoring native biomechanics after total hip arthroplasty (THA). Due to the large variation in patient morphology and pelvic kinematics, current technologies lack definition of what constitutes the optimal target alignment for an individual. Analyses of large series of problematic THAs confirm that apparently well-orientated components on standard radiographs can still fail due to functional component malalignment. Evidently, previously defined “safe zones” are not appropriate for all patients as they do not consider the dynamic behaviour of the hip joint. The first goal of this thesis was to understand the variation in patients’ pelvic kinematics to demonstrate the clinical importance of functional cup orientation. Secondly, the variation in femoral morphology across the THA population was investigated in consideration of how that might affect femoral component positioning. From these findings, a commercially-scalable method of analysing each patient’s individual hip dynamics prior to THA was developed. This enabled an optimal component alignment to be chosen for each patient, accounting for their specific morphology and dynamics. Finally, we developed a simple intraoperative method to achieve the predetermined optimal alignment utilising 3D printed custom guides. The end result is the Optimized Positioning System™ (OPS™), comprising preoperative dynamic planning and patient-specific instrumentation for delivery of a patient’s optimal component alignment. The technology has been commercialised globally and used in over 5,000 primary total hip replacements to date.