Cartilage-on-Cartilage Articulating System as a Wear Benchmark for Artificial Replacement Materials

A multidisciplinary study – with applications in engineering, tribology, biomechanics, orthopedics, biochemistry and biology – was conducted to establish a wear system that could be used to critically evaluate candidate artificial materials for clinical application in diarthrodial joint rehabilitation. More specifically, this study was conducted to examine the effects of articulating artificial materials against live cartilage by direct comparison to a model that articulated cartilage on cartilage. The goal of this study was met by addressing the following specific aims: 1) To modify the current material-on-cartilage setup to accommodate a cartilage-on-cartilage articulating system; 2) To investigate the effects of using synovial fluid as a lubricant in material-on-cartilage wear experiments as opposed to culture media; 3) To establish a cartilage-on-cartilage articulating system as a benchmark for material-on-cartilage wear experiments. Wear testing was performed in which cobalt chromium alloy (CoCrMo) balls or cartilage strips secured to polymer adapters were articulated against flat cartilage explants. All samples were cultured in constant temperature (37 ºC), humidity (95%) and CO2 level (5%) five days prior to wear testing. In order to apply load (40 N) and motion (±30° ball rotation; 5.2 mm migrating contact) a joint-motion simulator was used. A total of 16200 cycles at 0.5 Hz equally spread over three testing days was applied. A current method of articulating material on cartilage was modified to accommodate articulation of cartilage strips against flat cartilage explants. It was observed that synovial fluid performed significantly better than culture media as a lubricant with respect to maintaining the integrity of the cartilage matrix. It was also observed that cell viability of the explants significantly decreased when synovial fluid was used as the lubricant. The cartilage-on-cartilage model performed significantly better than the material-on-cartilage model with respect to maintaining matrix integrity, cell viability and surface topography characteristics during wear testing. Overall, the findings of this study have improved the current tribological methods of evaluating articular cartilage as well as candidate artificial materials for use in clinical joint rehabilitation treatments. Specifically, this study is directly applicable to clinical studies that facilitate hemiarthroplasties. The findings of this study may also lead to further development of critical evaluation methods and treatments involving articular cartilage and artificial materials.