86. Why are DBMs so variable? Influence of fibers, carrier, and tissue bank

Abstract

BACKGROUND CONTEXT Demineralized bone matrix (DBM) is widely used in spinal fusion. Most DBMs are particles combined with a carrier to provide putty-like handling. Demineralized bone fibers (DBF) are a formulation where allograft bone is demineralized in long fibers so the resulting DBF product is cohesive on its own. It has been suggested that 100% DBF products with no carrier may offer improved performance over particle-based DBMs with carrier. PURPOSE The objective of this study was to evaluate the variability of in vivo performance of DBFs from five different tissue banks with various differences in composition in a posterolateral fusion model. STUDY DESIGN/SETTING Seven different commercially available DBMs were evaluated from five different tissue banks: Four 100% DBFs, two DBFs with carrier, and one particle-based DBM with carrier. PATIENT SAMPLE Not applicable. OUTCOME MEASURES Not applicable. METHODS Single-level posterolateral fusion was performed in athymic rats. Fusion was assessed bilaterally after 4 weeks by manual palpation, radiograph and microCT (mCT) for bridging bone. Fusion mass maturity was assessed using an mCT grading scale and by histology. Statistical analysis was performed using Fishers Exact Test for categorical data, Kruskal-Wallis Test for non-parametric data, and linear regression for the relationship between fusion rate and % carrier. RESULTS Fusion end point assessments of manual palpation, radiography and mCT were closely concordant for all groups. The mCT fusion rates for the 100% DBF groups varied from 0 to 100%. The DBFs with carrier had mCT fusion rates of 0 to 81%. Within the same tissue bank, DBFs with carrier had slightly lower fusion rates than 100% DBF products, although differences did not reach statistical significance. For the DBM particulate with carrier, the fusion rate was 38%. There was an inverse linear correlation between fusion rate and percentage carrier composition (R2 = 0.99) for the carrier-containing groups. Histology and CT maturity grading revealed substantial differences in the quality of bone formation in the fusion mass, even among groups with similar fusion rates. CONCLUSIONS There were large variations in fusion performance for seven commercially available DBF/DBMs in an established preclinical fusion model. The fusion outcomes in this study suggest a detrimental effect of carrier on fusion outcomes. Among 100% DBF products, there were large variations in performance, suggesting that fiber composition alone does not guarantee outcomes. DBM variability is likely driven by variations in allograft processing conditions at different tissue banks, including differences in donor quality, fiber geometry, demineralization, storage, and sterilization procedures. In the absence of definitive clinical evidence, surgeons should carefully consider the tissue bank source using available data in valid animal models when selecting their DBF or DBM grafts. FDA DEVICE/DRUG STATUS Grafton (Approved for this indication), DBX Putty (Approved for this indication), Optium Putty (Approved for this indication).