Repair of large osteochondral defects with mix-mosaicplasty in a goat model

Osteochondral defects in weight-bearing regions must be repaired with cartilage and subchondral bone support simultaneously, as well as the integration between the 2, particularly in young, active patients. In this study, a new method called mix-mosaicplasty was used to reconstruct large osteochondral defects (6-mm diameter) in the weight-bearing region of the femoral condyle of goats. Two periosteum-bone plugs and 1 osteochondral plug harvested from the proximal tibia and intertrochlea groove were assembled to fill the defects in a mosaic mode. The goats were euthanized 16 weeks postoperatively, and the result of the repair process was assessed using macroscopy, morphologic analysis, electron microscope observation, glycosaminoglycan assay, and magnetic resonance imaging. Sixteen weeks postoperatively, the superficial surface of the defective region was covered with regenerated cartilage, and the periosteum-bone plugs were combined with each other. However, cleavage between cartilage plugs was noted. The donor site, which was filled with periosteum-bone plugs, was regenerated with fibrocartilage-like tissue. The repaired tissue was composed of small chondrocyte-like cells arranged tightly within an evenly distributed extracellular matrix containing type II collagen. Cells of the regenerated tissue in periosteum-bone plugs were smaller and distributed more densely. Electron microscopy demonstrated regular matrix fibers and abundant organelles within the repaired tissue. No significant differences of glycosaminoglycan content were observed between reconstructed tissue and normal hyaline cartilage. Magnetic resonance imaging revealed the healing process between plugs other than the control group. The new technique of mix-mosaicplasty can reconstruct full-thickness osteochondral compound defects in the weight-bearing region of the femoral condyle.