Fretting at modular junctions is thought to be a ‘mechanically assisted’ corrosion phenomenon, initiated by mechanical factors that lead to increased contact stresses and micromotions at the taper interface. We adopted a finite element approach to model the head-taper junction, to analyse the contact mechanics at the taper interface. We investigated the effect of assembly force and angle on contact pressures and micromotions, during loads commonly used to test hip implants, to demonstrate the importance of a good assembly during surgery. Models of the Bimetric taper and adaptor were created, with elastic-plastic material properties based on material tests with the actual implant alloy. FE contact conditions were validated against push-on and pull-off experiments. The models were loaded according to ISO 7206-4 and −6, after being assembled at 2-4-15kN, both axially and at a 30° angle. Average micromotions and contact pressures were analysed, and a wear score was calculated based on the contact pressures and micromotions.Background
Methods
The different types of treatment for osteonecrosis of the femoral head have not led to a consensus about which treatment is best for the different stages. Particularly in the later stages of osteonecrosis, the disease still progresses to destruction of the femoral dome. The purpose of our study was to check the outcome of bone impaction grafting used for the head-preserving treatment of severe femoral head osteonecrosis. In order to preserve the femoral head, the sphericity and mechanical properties of the femoral dome must be contained and further collapse prevented. In this prospective study, we included 28 hips in 27 patients who had severe complaints of pain due to an extensive osteonecrotic lesion. The mean age of the patients was 33 years with a mean follow up time of 42 months.Introduction
Methods
