Replacement of the Medial Tibial Plateau by a Metallic Implant in a Goat Model Roel J.H. Custers, 1 Daniel B.F. Saris, 1 Laura B. Creemers, 1 Ab J. Verbout, 1 Mattie H.P. van Rijen, 1 Simon C. Mastbergen, 2 Floris P. Lafeber, 2 Wouter J.A. Dhert 1,3 1 Department of Orthopaedics, University Medical Center Utrecht, P.O. Box 85500 3508 GA Utrecht, The Netherlands, 2 Department of Rheumatology & Clinical Immunology, University Medical Center Utrecht, The Netherlands, 3 Faculty of Veterinary Medicine, Utrecht University, The Netherlands Received 29 April 2009; accepted 4 September 2009 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jor.21021 ABSTRACT: The purposes of the present study were to explore the surgical possibilities for replacement of the medial tibial plateau by a metallic implant in a large animal model and to examine the implications for the opposing cartilage. In six goats, the medial tibial plateau of the right knee was replaced by a cobalt–chromium implant, using polymethylmethacrylate bone cement for fixation. The unoperated left knee served as a control. At 26 weeks after surgery, the animals were killed, and the joints evaluated macroscopically. Cartilage quality was analyzed macroscopically and histologically. Glycosaminoglycan content, synthesis, and release were measured in tissue and medium. All animals were able to move and load the knees without any limitations. Macroscopic articular evaluation scores showed worsening 26 weeks after inserting the implant (p < 0.05). Macroscopic and histologic scores showed more cartilage degeneration of the opposing medial femoral condyle in the experimental knee compared to the control knee (p < 0.05). Higher glycosaminoglycan synthesis was measured at the medial femoral condyle cartilage in the experimental knees (p < 0.05). This study shows that the medial tibial plateau can be successfully replaced by a cobalt–chromium implant in a large animal model. However, considerable femoral cartilage degeneration of the medial femoral condyle was induced, suggesting that care must be taken introducing hemiarthroplasty devices in a human clinical setting for the treatment of postmeniscectomy cartilage degeneration of the medial tibial plateau. ß 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res Keywords: tibial implant; cobalt–chromium; hemiarthroplasty; cartilage degeneration; goat model The knee menisci are wedge-shaped, semilunar discs of fibrocartilage, interposed between the tibia and the condyles of the femur. Damage to, or removal of, the menisci alters static load transmission, shock absorp- tion, joint lubrication, and stabilization of the knee 1–4 and is associated with articular cartilage degenera- tion. 5,6 In the medial compartment, degenerative changes appear to be proportional to the amount of menisci removed and the postoperative period. Several in vivo studies demonstrated that chondral lesions appear earlier and more intensively in the tibial plateau than in the femoral condyle. 7,8 Therefore, a medial meniscectomy in animals is frequently used as a model for knee osteoarthritis. 9 Currently, a growing number of strategies are available to replace menisci that have been irreversibly damaged or that have been operatively removed. Such replacement therapies are promising, but are not completely protective from cartilage degeneration. 10 When tibial cartilage degeneration has progressed extensively, the joint might not benefit from a meniscus replacement. Alternatively, the degenerated medial tibial plateau might be replaced by a metallic prosthesis, to slow the degeneration and conserve the femoral condyle cartilage. Therefore, the purposes of the current study were to use an in vivo goat model to explore the surgical possibilities for replacement of the medial tibial plateau, after a partial medial meniscectomy, by a cobalt–chromium (CoCr) implant and to examine the implications for the opposing cartilage. The contralateral unoperated knees were used as controls. MATERIALS AND METHODS Experimental Design This research was approved by the Institutional Animal Care Committee of the Utrecht University. In adult goats, the right medial tibial plateau was replaced by a CoCr implant (fixed using polymethylmethacrylate bone cement), removing the anterior part of the medial meniscus and leaving the cruciate and the collateral medial ligaments intact. The unoperated left knee served as a control. The animals were killed 26 weeks after surgery. Macroscopic evaluation of the articular compart- ments was performed immediately before replacing the medial tibial plateau and after treatment. Tibial and femoral cartilage quality was evaluated by macroscopic, histologic, and bio- chemical analysis. Animals Six adult female Dutch milk goats with a mean age (and SD) of 2.4  0.28 years and a mean weight of 56.6  8.4 kg were used for surgery. Food and water were given ad libitum. General health and care conditions were monitored by the laboratory animal welfare officer. Implants Implants were custom-manufactured to our design specifica- tions by Smith & Nephew (Memphis, TN, USA). The CoCr components were produced from a cast CoCr alloy (ASTM F75), and the articulating surface was polished (R a < 0.03 mm). The shape of the implant was designed after a study on cadaver knees and testing in a pilot study (Fig. 1). The implant JOURNAL OF ORTHOPAEDIC RESEARCH 1 Correspondence to: Daniel B.F. Saris (T: þ31887556971; F: þ31302510638; E-mail: d.saris@umcutrecht.nl) ß 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.