Abstract
Introduction: Wear, and the resultant loosening and revision, of Total Hip Replacements (THRs) remains the limiting factor in the long term success of the prosthesis. Over 1 million Total Hip Replacements (THRs) are implanted each year, of which about 15% are revisions, most of which are a consequence of loosening of either femoral or acetabular components. This is frequently caused by either the mechanical (Wroblewski, 1986) or biological (Besong et al, 1997) response to the wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular component.
In a previous study Bennett (2002, 2000) has demonstrated that the walking patterns of THR patients 5 years post operation directly correlated with the wear of the acetabular component, as measured radiographically. The present study considers THR patients 10 years post-operatively, ensuring more accurate wear measurements and more meaningful outcome measures.
Materials and Methods: Gait Analysis was performed on a number of THR patients following routine review using a Vicon 370 data capture system and a lower body marker set. This data was processed using Polygon software and joint angles were derived for the hip in the sagittal, coronal and transverse planes. A computer simulation was used to determine the path which each of 20 points on the prosthetic femoral head traces on the acetabulum during walking.
Results: It was found that patients exhibited different patterns of movement ranging from liner to multi-directional. Normal subjects have previously been found to exhibit multi-directional movement. Patients with mult-directional movement showed evidence of greater wear (Bennett et al., 2000).
Discussion and conclusion: Linear movement causes orientation hardening and wear resistance while multi-directional movement cause increased shear and greater wear rates. These differences in movement loci have a significant influence on UHMWPE wear rate and the long term survival of the implant.
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.
References:
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