The effect of the transverse component of the hip reaction on cement mantle stresses in a model of an implanted Exeter™ prosthesis

Abstract

Clinical studies have attributed considerable importance to the torsional loading of prosthetic femoral implants; however, the effect of this load has frequently been neglected in load simulations of the hip. The objective of this study, therefore, is to investigate the effects of the transverse joint load component in a model analysis of the proximal femur. Cement mantle stresses in a three-times full-size model of an Exeter™ total hip replacement were investigated using three-dimensional embedded strain transducers. Six sites were analysed for two separate loading configurations, namely the two-dimensionally loaded single-legged stance and the ‘toe off’ phase of gait which represents a three-dimensional hip reaction. Results showed a considerable variation in stem/cavity contact conditions due to the application of the transverse load component. Furthermore, large distal bending stresses are induced in the sagittal plane, with considerable shearing stresses due to torsion evident at all sites. The study highlights the significance of the transverse load and emphasizes the considerable limitations of finite element studies in modelling realistic load-dependent interface conditions.