Cartilage degeneration in the goat knee caused by treating localized cartilage defects with metal implants

The purpose of the current study was to investigate the feasibility of applying defect-size femoral implants for the treatment of localized cartilage defects in a 1-year follow-up model.

In 13 goats, a medial femoral condyle defect was created in both knees. Defects were randomly treated by immediate placement of an oxidized zirconium (OxZr) (n=9) or cobalt-chromium (CoCr) implant (n=9) or left untreated (n=8). Six un-operated knee joints served as a control. Animals were sacrificed at 52 weeks. Joints were evaluated macroscopically. Cartilage quality was analyzed macroscopically and microscopically and cartilage repair of untreated defects was scored microscopically. Glycosaminoglycan (GAG) content, release and synthesis were measured in tissue and medium. Implant osseointegration was measured by automated histomorphometry.

Cartilage repair score of the defects was 13.3+/-3.0 out of 24 points (0=no repair, 24=maximal repair). Articular evaluation scores decreased (indicative of degeneration) in untreated defects and in defects treated with either implant (P<0.05). Macroscopical, microscopical and biochemical analysis showed that the presence of untreated defects and the implants caused considerable degeneration of medial tibial plateau, and to a lesser extent of the lateral compartment. Mean bone-implant contact was extensive and not different between materials (39.5+/-28.1% for OxZr and 42.3+/-31.5% for CoCr) (P=0.873).

Considerable cartilage degeneration was induced in the articulating cartilage of the medial tibial plateau 1 year after creating an osteochondral defect in the medial femoral condyle. Treating this defect with a small metal implant, made of either OxZr or CoCr, could not prevent this degeneration. Further optimization of defect-size implants and their placement is required to make this the therapy of choice for the treatment of local cartilage defects.