Background: Localized cartilage defects are frequently associated with joint pain, reduced function, and a predisposition to the development of osteoarthritis. The purposes of the current study were to investigate the feasibility of the application of defect-sized femoral implants for the treatment of localized cartilage defects and to compare this treatment, in terms of joint degeneration, with the use of microfracture in a goat model of established cartilage defects.
Methods: In nine Dutch milk goats, a defect in the medial femoral condyle was created in both knees. After ten weeks, the knees were randomly treated by microfracture or by placement of an oxidized zirconium implant. At twenty-six weeks after surgery, the animals were killed. The joints were evaluated macroscopically. Implant osseointegration was measured by automated histomorphometry, and cartilage repair (after microfracture) was scored histologically. Cartilage quality was analyzed macroscopically and histologically. Glycosaminoglycan content and release were measured by alcian blue assay, and the synthesis and release of newly formed glycosaminoglycans were measured by liquid scintillation analysis of the incorporation of 35SO42— in tissue and medium.
Results: The mean bone-implant contact (and standard error) was appropriate (14.6% ± 5.4%), and the amount of bone surrounding the implant was extensive (mean, 40.3% ± 4.0%). The healing of the microfracture-treated defects was extensive, although not complete (mean, 18.38 ± 0.43 points of a maximum possible score of 24 points). The macroscopic cartilage evaluation did not show any significant differences between the treatments. On histologic evaluation, the cartilage of the medial tibial plateau articulating directly against the treated defects demonstrated significantly more degeneration in the microfracture-treated knees than in the implant-treated knees (p < 0.05). This was in accordance with a significantly higher glycosaminoglycan content, higher synthetic activity, and decreased glycosaminoglycan release of the medial tibial plateau cartilage of the implant-treated knees (p < 0.05 for all). On histological analysis, degeneration was also found in the cartilage of the lateral tibial plateau and condyle, but no significant difference was found between the treatments.
Conclusions: Both microfracture and the use of implants as a treatment for established localized cartilage defects in the medial femoral condyle caused considerable (p < 0.05) degeneration of the directly articulating cartilage as well as in more remote sites in the knee. However, in the medial tibial plateau, the metal implants caused less damage than the microfracture technique.
Clinical Relevance: Although this study shows that small metal implants may be more suitable than microfracture in the treatment of localized cartilage defects in the knee, the generalized degeneration found following both treatments should be addressed first.