Hydroxylapatite supported Dacron plugs for repair of isolated full-thickness osteochondral defects of the rabbit femoral condyle: mechanical and histological evaluations from 6-48 weeks.

The early degeneration of neocartilage commonly observed after experimental cartilage repair is attributed in part to the impaired cartilage-bone mechanics caused by an insufficient regrowth of the subchondral bone plate. In order to enhance bone regrowth after cartilage repair Dacron plugs supported by hydroxylapatite were implanted into 3 mm diameter full-thickness defects of both medial femoral condyles in 21 rabbits. In addition, the plug in one knee of each animal was wrapped with autologeous periosteum from the proximal tibia. The repair sites were evaluated at 6, 12, 24, and 48 weeks. Except for the mechanics of the repair site at 24 weeks additional periosteum did not improve the overall results. In specimens with additional periosteum the compression compliance of the repair sites improved gradually from abnormal high to almost normal values at 24 weeks, but were found softened again at 48 weeks. All other repairs were softer than normal cartilage at all time intervals. In all specimens a well-defined but irregularly shaped, subchondral bone plate had developed by 12 weeks. The neocartilage was initially thicker than normal cartilage, but the thickness decreased gradually and reached normal values by 48 months. Neocartilage formation with moderate morphological scores appeared already at 6 weeks, but the scores did not improve with time. High variations in quality of the regenerated tissue, from insufficient regeneration to hyaline-like cartilage, were found at all time intervals, but none of the specimens had developed normal cartilage. Most knees had a low-grade synovitis and some had particle debris.