Abstract
Introduction: The acetabular cup comprises a 3mm thick bearing surface of UHMPE, a 1.5mm backing of 30% carbon fibre reinforced polybutyleneterephthalate (CFRPBT). Young’s modulus, of CFRPBT layer is similar to natural subchondral bony plate. The cup deforms, when loaded, with the surrounding acetabular bone so that micro-motion at the bone-prosthesis interface is reduced. We measured BMD in the periacetabulum
Method: BMD was analysed for 2 years (n=11 females) with Mean Barthel Index at 2 years 19. Regions of interest were defined according to De-Lee and Charnley (ROI I-III) for the acetabulum. BMD during follow-up was compared with immediate post-operative values. Mean precision error (CV%) was 1.8±0.87%.
Results: By 2 years the mean BMD in HA cup was 0.73gms/cm2 representing a decrease of 7% and 0.78gms/cm2, which representing a 4% decrease with the non-HA cup. With the HA cup at 2 years we measured an increase in ROI I of 3% and a reduction in ROI II and III of 3% and 20% respectively. With the non-HA cup at 2 years we measured an increase in ROI II of 7% and a reduction in ROI I and III of 3% and 16%. There was a significant difference (p< 0.05) in the BMD changes measured in non-weight bearing zone III and one of the weight bearing zones (zone II).
Conclusion: Changes in BMD measured reflect a pattern of maximally reduced stress in zone III followed by zone II and least in the load bearing axis of the acetabulum zone I.
Theses abstracts were prepared by Mr Peter Kay. Correspondence should be address to him at The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
