The influence of cup anteversion on total hip arthroplasty dislocation mechanisms

[INTRODUCTION] Dislocation continues to be a common complication of total hip arthroplasty (THA). Many in vitro studies have reported the range of motion (ROM) of the hip, impingement, and dislocation mechanism, but the influence of muscle and soft tissue remains little explored. Many factors affect the prevalence of dislocation after THA, including soft tissue laxity, surgical approach, component position, patient factors, and component design [1]. Bartz et al. investigated the dislocation mechanism using in vitro cadaver simulation with load cables to simulate muscle actions, and reported spontaneous dislocation that occurred without impingement [2]. An in vivo intraoperative study suggested soft tissue traction could be one major reason for subluxation or dislocation with hip flexion and internal rotation [3]. These studies suggest that soft tissue might play an important role for dislocation after THA. In this study, we used a threedimensional numerical model to calculate all muscles forces crossing the hip and predict the soft-tissue tension and force directions. This numerical model has been validated with intraoperative in vivo measurements. The objective of this study was to investigate the effects of the acetabular cup anteversion angles on ROM and dislocation mechanism using a numerical model that includes the effects of softtissue tension.