Abstract
Background
High cup abduction angles generate increased contact stresses, higher wear rates and increased revision rates. However, there is no reported study about the influence of cup abduction on stresses under head lateralisation conditions for ceramic-on-Ceramic THA.
Material and method
A finite elements model of a ceramic-on-ceramic THA was developed in order to predict the contact area and the contact pressure, first under an ideal regime and then under lateralised conditions. A 32 mm head diameter with a 30 microns radial clearance was used. The cup was positioned with a 0°anteversion angle and the abduction angle was varied from 45° to 90°. The medial-lateral lateralisation was varied from 0 to 500 microns. A load of 2500 N was applied through the head center.
Results
For 45° abduction angle, edge loading appeared above a medial-lateral separation of 30 μm. Complete edge loading was obtained above 60 μm medial-lateral separation. For 45 degrees inclination angle, as the lateralisation increased, the maximal contact pressure increased from 66 MPa and converged to an asymptotic value of 205 MPa. A higher inclination angle resulted in a higher maximum contact pressure. However, this increase in contact pressure induced by higher inclination angle, became negligible as the lateral separation increased
Discussion Both inclination angle and lateral displacement induced a large increase in the stresses in Ceramic-on-Ceramic THA. Edge loading appeared for a small lateralisation. The influence of acetabular inclination angle became negligible for a lateral displacement above 240 μm, as the stresses reached an asymptotic value.
