Wear and Migration in Cemented Total Hip Arthroplasty
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Background: In THA the aim is to offer lasting functional improvement and pain relief. Several variables affect the longevity in THA. New materials in the acetabular cup and femoral head components have been developed to reduce wear, and thus improve longevity. Several different designs have been introduced to optimize implant fixation. Component orientation has been suggested as a variable influencing wear in THA. The purpose of this thesis was to compare new and traditional materials and designs features used in cemented THA. We also wanted to investigate whether the acetabular cup inclination angle affected wear.
Methods: 150 patients were randomized to receive five different articular bearings with two different femoral stems. Wear and fixation of the components was evaluated with radiostereometric analysis (RSA) at 2 years follow-up.
Results: The use of HXLPE instead of conventional PE substantially reduced wear at 2 years. The use of oxidized zirconium femoral heads did not reduce wear compared to CoCr. The Charnley Ogee cup was not outperformed by the more recently introduced implants in our study. The Spectron EF femoral stem was more stable than the Charnley flanged 40 stem in our study when evaluated at 2 years. We found no relationship between the inclination angle of the acetabular component and wear or cup migration.
Interpretation: Further follow-up is required to discern differences between CoCr and Oxinium heads with respect to wear, implant durability, and clinical benefits. Based on concerns of the mechanical properties and the lack of long-term clinical follow-up studies, we recommend the use of Oxinium to be restricted to clinical studies. Our results of the HXLPE cup confirm the results of other reports. Initial femoral stem stability is not invariably related to good long-term results. Our results emphasize the importance of prospective long-term follow-up of prosthetic implants in clinical trials and national registries, and stepwise introduction of implants. Concerns other than polyethylene wear and migration must be considered in conjunction with the inclination angle of cemented all-polyethylene acetabular components. An optimal angle of inclination for the acetabular component may be of greater importance with hard-on-hard bearings. We conclude that the Charnley prosthesis still represents a standard against which new implants can be measured.