Abstract
In vivo and in vitro studies of ceramic on ceramic (COC) bearings have demonstrated that swing phase microseparation followed by the impact of the femoral head on the superior acetabular insert rim leads to accelerated wear. However, resultant wear remained low. The wear of ceramic on polyethylene (COP) and metal on metal (MOM) couples under swing phase microseparation is unknown, this study aimed to compare the wear of these total hip replacements under standard and microseparation conditions.
A physiological hip simulator was used, loads and motions were applied to approximate in vivo conditions. Microseparation was achieved by displacing the femoral head inferiorly during swing phase, the head contacted the inferior cup rim and was laterally displaced. On heel strike the head contacted the superior cup rim prior to relocation. Components (as shown in table 1) were tested for 5 million cycles, at a frequency of 1 hertz in 25% (v/v) new born calf serum. Under standard conditions, wear of COC and MOM bearings was significantly lower than wear of COP couples. Under microseparation conditions the COC and MOM wear increased by 4 and 25 times respectively. Microseparation conditions reduced wear of COP couples by a factor of 4. Creep deformation and damage to the UHMWPE cup rim was observed, however, wear remained low. It is postulated that this reduction in polyethylene wear is due to the separation of the components in swing phase improving the entrapment of lubricant, hence wear is reduced via a squeeze film lubrication mechanism.
These abstracts were prepared by Mr Peter Kay. Correspondence should be addressed to him at The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
