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Abstract:Hemiarthroplasty is one method used to treat osteoarthritic joints. Often, however, an adverse response of the articular cartilage to the metal implants occurs. The purpose of this study was to evaluate and compare the response of a surgically created defect to pyrolytic carbon and cobaltbased alloy hemiarthroplasties. The cartilage on the lateral side of the tibial plateau of a canine knee joint was abraded to create a full-thickness defect. Two small holes were drilled into the exposed subchondral bone. Next, either a carbon or metal implant was placed in the lateral femoral condyle. The implantation period was 1 year. Histologic examination of the tibial defects revealed a smooth bony surface for both implant groups. In addition, there was no evidence of a residual adverse inflammatory response nor of a significant increase in subchondral bone formation for either group. Surface cracks resulting from the presence of the implant were seen in 14% of the carbon implant specimens and in 100% of the metal implants. Fibrocartilage regeneration was seen in 86% of the carbon implants and in 25% of the metal implants. Thus the carbon appears to be better tolerated mechanically compared to wrought cobalt-chromium alloy. Pyrolytic carbon shows promise for use in hemiarthroplasty.