Finite Element Analyses on Total Hip Arthroplasty DislocationMechanisms

Abstract

This study is aimed to calculate the range of motion of total hip arthroplasty (THA) until implant-to-implant impingement and dislocation occur, and to calculate resisting moments to dislocate the hip using non-linear finite element (FE) methods. To analyse the dislocation objectively and to clarify the distinction between implant-to-implant impingement and dislocation, three-dimensional FE models of hybrid THA components were generated. In this study, posterior dislocation-prone maneuvers such as flexion, adduction, internal rotation, and their combinations were analysed. The analyses were started with the femoral component oriented in a manner corresponding to the hip being flexed to the impingement occurrence angles at various internal rotation and adduction angles. The muscle forces were also considered by applying hip joint forces during the analyses. As results, the angles of internal rotation and adduction affected both impingement and dislocation angles of flexion. The flexion angles both at impingement and at dislocation decreased by increasing the internal rotation angles. Although the peak flexion moment todislocate the hip joint increased by increasing the internal rotation angle, it didn't always increase with an increase in the adduction angle. The highest value of the peak flexion moment to dislocate the hip was observed at 30° of internal rotation. Conversely, the lowest value of the peak flexion moment was observed at 10° of adduction. This lowest value means that the hip joint is easy to be dislocated at this adduction angle by an external torque.