Edge loading is a common wear mechanism in Metal-on-Metal (MOM) hip resurfacing and is associated with higher wear rates and the incidence of pseudotumour. The purpose of this study was to develop a method to investigate the contributions of patient, surgical and implant design variables on the risk of edge loading. We created a mathematical model to calculate the distance from the head-cup contact patch to the rim of the cup and used this to investigate the effect of component position, specific design features and patient activity on the risk of edge loading. We then used this method to calculate the contact patch to rim distance (CPRD) for 160 patients having undergone revision of their MOM hip resurfacing in order to identify any possible associations.Introduction
Method
It has been speculated that impact deformation of thin 1-piece cups used for modern metal-on-metal hip replacement may contribute to early failure. The purpose of this study was to reproduce typical impact deformation and quantify the effect of this on the frictional torque generated at the hip. We tested nine hip couples of three designs (the ASR, BHR and Durom) and three sizes (42mm, 46mm and 50mm). A custom compression device was designed to replicate the in vivo forces and impact deformation of 1-piece metal cups reported in the literature. Each cup was mounted in the device, which itself was mounted on a mechanical testing machine. The cups were compressed with incremental loads up to a maximum of 2000N. At each increment we measured cup deformation, and then the head component was seated into the cup. The hip was lubricated and the head component rotated 60 degrees axially within the cup and the axial torque was measured.Introduction
Methods
