Demineralized allogeneic bone matrix for cartilage repair.

We tested the chondrogenic potential of demineralized allogeneic bone matrix (DABM) in the repair of osteochondral defects. In 42 adult rabbits, a 5-mm2 or 15-mm2 defect was created bilaterally in the intercondylar groove of distal femur. DABM was inserted directly in 37 defects, whereas in 35 it was inserted after previous placement in muscle for 4, 16, or 19 days. Another 12 defects were left empty, serving as controls. Subgroups of animals were killed at 6, 12, 18, and 26 weeks. The distal femora were excised and prepared for histologic evaluation in hematoxylin-eosin and toluidine blue. Cartilage-like repair tissue was observed in the majority of defects. However, there was a great variability in the experimental groups without any clear relationship to type of DABM implant, defect size, or postoperative time. Even individual knees exhibited varying stages of cartilage differentiation. Overall, DABM placed in muscle for 19 days appeared to yield the best repair of the defects. The most consistent findings of the present study were bone formation in the marrow of distal femur and, notably, the absence of bone differentiation toward the joint surface. Hence, it seems that the synovial environment prevents bone formation otherwise induced by DABM in vascular tissue. Although tissue formed in articular defects supplemented with DABM is of cartilaginous differentiation, which is retained over time, it is of highly variable quality. Hence, the described approach has to be optimized before it can be applied for the purpose suggested.