Advancing Hemiarthroplasty: Predicting in vivo performance of cartilage bearing systems through benchtop and ex vivo testing.

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ABSTRACT The ultimate goal of this research program is to advance hemiarthroplasty performance. Hemiarthroplasty involves replacement of one of the articular joint surfaces with an artificial bearing surface. It offers a clear benefit in patients with localized cartilage damage, preserving the healthy bone and cartilage in the joint to maximize future treatment options. And hemiarthroplasty is inherent in the replacement of individually diseased carpal (wrist) or tarsal (foot) bones, which have multiple articulations with neighboring bones. Currently, hemiarthroplasty outcomes vary dramatically by the joint involved and by the type of bearing surface used to articulate with the opposing cartilage. Failure most often occurs by degeneration of the opposing articular surface. A critical challenge in advancing hemiarthroplasty performance is the ability to identify bearing surfaces that will maintain healthy cartilage. There are numerous candidate biomaterials that might be suitable for use as hemiarthroplasty bearing surfaces, including metals, ceramics, and polymers, as well as specialized coatings, such as titanium nitride and pyrolytic carbon. However, the performance of these materials has been mixed, due in large part to the lack of standardized and validated testing methodologies. Accordingly, the specific objective of this project is to develop a model where benchtop and ex vivo testing can predict the cartilage response to hemiarthroplasty bearing system wear in a fit-for-purpose large animal model. This goal will be achieved by completing three specific aims. In the first, we will characterize the material and mechanical properties of eight candidate hemiarthroplasty bearing surfaces (2 metals, 4 polymers, 1 ceramic, and 1 pyrolytic carbon) using standard benchtop mechanical tests (roughness, wettability, modulus, hardness, and wear testing against cortical bone). In the second, we will characterize the cartilage bearing performance of each of the candidate biomaterials by wear testing them against bovine cartilage plugs in a joint motion-simulating biotribometer, using proteoglycan/glycosaminoglycan (PG/GAG) and hydroxyproline as measures of cartilage matrix degradation and live/dead assays as a measure of cell damage. In the third, we will test four of the 8 materials from Aims 1 & 2 as bearing surfaces in a novel unicompartmental tibial hemiarthroplasty model in the Yucatan minipig, measuring cartilage damage (macro- and microscopic), synovial inflammation, cartilage thickness, and osteophyte bone formation at 52 weeks. And finally, we will develop a statistical model where the data from Aims 1 and 2 can be used to predict the outcome in Aim 3. The work outlined in this proposal will yield a model where benchtop and ex vivo testing can predict the cartilage response to hemiarthroplasty. This project will provide a crucial tool needed to accelerate the design, development, and FDA clearance of new hemiarthroplasty bearing surfaces, resulting in a significant benefit for millions of patients afflicted with degenerative joint disease.