Cartilage damage caused by metal implants applied for the treatment of established localized cartilage defects in a rabbit model

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Abstract
The purpose of the current study was to investigate the feasibility of the application of defect‐size femoral implants in a rabbit model of established cartilage defects and compare this treatment to microfracturing. In 31 New Zealand White rabbits, a medial femoral condyle defect was created in each knee. After 4 weeks, 3 animals were killed for defect baseline values. In the other 28 rabbits, knees were sham‐operated, treated with microfracturing, or treated by placing an oxidized zirconium (OxZr) or cobalt‐chromium (CoCr) implant (∅︁ articulating surface 3.5 mm; fixating pin of 9.1 mm length). These animals were sacrificed 4 weeks after treatment. Joints were evaluated macroscopically. Implant osseointegration was measured by automated histomorphometry, and cartilage repair was scored microscopically. Cartilage quality was analyzed macroscopically and microscopically. Bone–implant contact was 63.2% ± 3.2% for CoCr and 62.5% ± 3.2% for OxZr. Cartilage defects did not show complete healing, nor during subsequent sham‐surgery or microfracturing. For all treatments, considerable cartilage damage in the articulating medial tibia, and degeneration of lateral tibial and femoral cartilage was observed (p < 0.05). Both CoCr and OxZr implant‐treated defects showed an increase of cartilage degeneration compared to microfracturing and sham‐operated defects (p < 0.05). Although only a single short‐term follow‐up period was investigated in this study, caution is warranted using small metal implants as a treatment for established localized cartilage defects because, even after 4 weeks in this model, the metal implants caused considerable degeneration of the articulating surface. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:84–90, 2009

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