Optimizing demineralized freeze-dried bone allograft for treating bone defects

Demineralized freeze-dried bone allograft (DFDBA) is used clinically for treating bone defects, in part because of its osteoinduction ability. However, there is considerable controversy concerning its effectiveness in this regard. We developed an in vivo assay to examine whether variability in commercial preparations of DFDBA exist among bone banks, and between batches within individual bone banks. DFDBA (14 batches from 6 bone banks) was implanted in muscle pouches in the calf of nude mice. After 56 days, the implanted tissue was harvested and histologic sections were examined for the presence of new bone using a semi-quantitative grading system. The same sections were analyzed by histomorphometry to determine the area of new bone and the area of residual DFDBA. This study showed that considerable variability did exist. We then examined 27 batches from a single bank to determine if the variability could be due to donor age or gender. The results indicated that bone from donors over 50 years of age had little or no bone induction ability. We also compared DFDBA from young, adult, and old rats and found that the DFDBA became remineralized in a donor-age dependent manner indicating biochemical differences exist as a function of age. Finally, we showed that inactive DFDBA could be used as an osteoconductive substrate for rhBMP-2, thus making even poor DFDBA clinically useful.