Patella femoral joint bearings in total knee replacements have shown low wear (3.1 mm3/MC) under standard gait simulator conditions1. However, the wear in retrieval studies have shown large variations between 1.3 to 45.2 mm3/year2. Previous in vitro studies on the tibial femoral joint have shown wear is dependent on design, materials and kinematics3. The aim of this study was to investigate the influence of the design (geometry) and shape on the wear rate of patella femoral joints in total knee replacements. The Leeds/Prosim knee simulator was used to investigate the wear of two types of commercially available patellae. The PFC Sigma cobalt chrome femoral component was coupled with 2 types of patellae buttons: round and oval dome. The UHMWPE was the same for the both types – GUR1020 GVF (gamma irradiated in vacuum and foiled packed). 25% bovine serum was used as the lubricant. The test were carried out at three conditions – high medial lateral (ML) rotations (<4°) and uncontrolled ML displacement (<4 mm), low ML rotation (<1°) and uncontrolled ML displacement (<4 mm); the physiological gait cycle; and low ML rotation and controlled ML displacement (<1.5 mm). In this abstract the two designs were tested in physiological gait condition (Figure 1). Patella ML displacement and tilt were passively controlled and measured after every 300,000 cycles. A ligament resisting force equivalent to 10 N4 was applied on the lateral side of the patella to avoid patella slip. Five samples of each design were tested for 3 million cycles at a cycle rate of 1 Hz. The wear volume was obtained gravimetrically every million cycles and presented with 95% confidence limits. Statistical significance was taken at p<0.05.Introduction
Materials and Methods
