INTRODUCTION: DBM‐based products are most commonly used with autograft, allografts, and possibly BMPs. Very few of these DBM‐based products have been systematically evaluated in vivo. Fewer of these DBM‐based products have been evaluated when combined with autografts, allografts, or DBMs. Previously we have reported fusion variability across different production Lots of these DBM‐based products. Recent studies have shown both intra product variability (lot‐to‐lot variability due to production lots) and inter product variability (product formulations). The purpose of this study was to assess the benefit of a sub efficacious dose of rhBMP‐2, or autogeneous bone added to a DBM‐based product.
METHODS: A L4‐5 posterolateral lumbar spinal fusion was performed on athymic rats with implantation of 3 unique Lots of DBM‐based product (EquivaBone, Etex Co.) with and without subefficious dose of 0.006 mg/ml rhBMP2+DBM‐based product. Each combination was tested on 4 rats total. Fusion success was determined at eight weeks and 6 months with use of radiographs and manual palpation of the vertebral segments. Fisher's exact test and Logistic regression were used to determine the difference and predictive abilities of assayed and added BMPs.
RESULTS: All segments implanted with 0.006 mg/ml rhBMP2/ACS only were not fused; however all segments implanted with the same dose of rhBMP2/ACS combined with DBM‐based product were fused. Also, when 25% DBM and 25%CP was used with 50% ICBG fusion was also seen in all the animals after 6 months.
DISCUSSION: Fusion was not observed with the low dose rhBMP2/ACS only. The higher the quantity of DBM to CP base in the product, the more rapid the bone formation. The optimal ratio between DBM and CP was 75% DBM to 25% CP. Low doses of rhBMP‐2 added to DBM product enhanced remodeling and rapid bone formation at all ratios of DBM to base. As is clinically practice, autogeneous bone added to the DBM‐based product also enhanced rapid bone formation.