| Description |
This dissertation presents a series of research projects aimed at uncovering the causes of severe wear in ceramic-on-ceramic (CoC) hip prostheses and at devising novel contact and wear test methods that accurately replicate its root cause mechanics. CoC prostheses can provide lower wear rates than other types of prostheses; however, their clinical adoption has been inhibited by reports that they are liable to squeak annoyingly. Prior authors have theorized that acetabular edge loading is a precursor to squeaking. In this dissertation, one project has demonstrated the suitability of Hertzian contact theory for predicting the contact mechanics of edge-loaded CoC implants. Another project has shown that a small manufacturing artifact on the edge of ceramic acetabular liners exacerbates edge-loading wear. A third project has discovered the key to reproducing lubricated, recurrent CoC squeaking in vitro using a novel testing approach. The culminating project has engineered a novel approach to averting the CoC squeaking problem. This project has designed and validated a new wear test method to efficiently evaluate ceramic materials' edge-loading wear performance. The new method uses simply shaped surrogate test specimens to substitute for full-scale ceramic hip implants, with the surrogates designed to accurately replicate the severe edge-loading contact stresses of the implants. Three series of wear tests were performed, one using the new approach with surrogate specimens, and the other two using a more direct but complicated approach with edge-loaded full-scale implants; each series included three different ceramic material pairs. The first key outcome was that the surrogate test series yielded the same wear factor ranking as the two series performed using the more complicated method. The second key outcome was that the materials exhibited similar temporal trends in the measured friction force, which implies that the materials became damaged and fragmented by essentially the same mechanisms. These congruent results, comparing surrogate and full-scale test methods, demonstrate that the project has achieved its overarching objective of developing a simple, surrogate specimen wear test that will facilitate screening a larger pool of candidate new materials, at early stages in their development, for their wear performance under severe edge-loading contact stresses. |
