Augmented demineralized bone matrix: a potential alternative for posterolateral lumbar spinal fusion.

Variable osteoinductive potential has been reported between and within production lots of different demineralized bone matrix (DBM) products. This study compared fusion rates of different manufactured lots and augmented formulations of DBM with a dose-response curve of recombinant human bone morphogenetic protein 2 (rhBMP-2) on inactivated DBM carrier in a posterolateral fusion rat model. Lumbar fusions were performed in 145 rats. In the control rats, we implanted autograft, graft alternative, including inactivated DBM, or nothing (ie, no graft). In the study rats, we implanted 1 of 2 BioSETR (RTI Biologics, Alachua, Florida) DBM lots, growth factor-enriched DBM, and inactivated DBM plus rhBMP-2 in different concentrations. Manual palpation revealed fusion rates of 25% (autograft), 0% (inactivated DBM), 17% (DBM donor A), and 36% (DBM donor B). The fusion rate of the most enhanced donor B graft (83%) was higher (P<.05) than that of autograft or unenhanced DBM. Inactivated DBM plus rhBMP-2 fused between 45% and 100%. There was no significant difference between DBM plus rhBPM-2 and the highest enrichment group of donor B. Differences between 2 DBM lots in an athymic rat ectopic bone formation model also were found in the spine fusion model. Enhanced DBM formulations were comparable with inactivated DBM plus rhBMP-2 with respect to performance and could represent a bone graft alternative in spine fusion.

Demineralized bone matrix as an osteoinductive biomaterial and in vitro predictors of its biological potential.

The osteoinductivity of demineralized bone matrix (DBM) varies from donor to donor as a result of varying levels of multiple growth factors, matrix integrity, and artifacts from material processing. Many in vitro assays are currently used for screening the osteoinductivity of DBM. The objectives of this study were to determine the correlation of specific growth factors and in vitro mitotic stimulation to in vivo ectopic bone formation capacity with a large number of DBM samples. Samples were assayed using ELISA methods for BMP-2/4 and TGF-beta1 (n = 304) and cell proliferation using SAOS-2 osteoblasts (n = 239). All samples were then implanted intramuscularly in the abdomen of nude rats. All in vitro assays showed significant variability for any particular level of ostoinductivity determined by in vivo model. A significant, but only very weak, positive correlation to in vivo results was found for TGF-beta1 (r(2) = 0.016), BMP 2/4 (r(2) = 0.065), and SAOS-2 cell proliferation (r(2) = 0.053). The results of this study amplify the notion that a multitude of factors and their relative interplay, rather than a single factor are likely to determine the potency of any particular lot of DBM.