Purpose: B2A2-K-NS (B2A) is a synthetic receptor-targeted peptide that appears to amplify the biological response to rhBMP-2. In ectopic sites in vivo, B2A augments bony mineralization when combined with demineralized bone matrix. The purpose of this study was to determine if the synthetic peptide B2A2-K-NS coated on osteoconductive granules (B2A/G) enhances autograft fusion in a rabbit bilateral posterolateral spine fusion model.

Method: Sixty skeletally mature New Zealand White Rabbits weighing 4.5–5.5 kg were entered into the study (IACUC #0511251). A single-level, bilateral posterolateral intertransverse process fusion was performed at L4-L5 with autogenous bone or an osteoconductive granule containing several coating concentrations of B2A. Animals were euthanized at 6 weeks post surgery.

Results: Gross examination of the surrounding soft tissues and grafted area showed no adverse reactions to the osteoconductive granules with or without B2A. Radiographic fusion rates were similar to palpation fusion rates across all groups. When assessed by palpation, animals treated with 300 μg B2A/G had 80% fusion while those treated with 100 μg B2A/G (89%) and 50 μg B2A/G had 78% fusion. Animals receiving 0 μg B2A/G (granules only) had a fusion rate of 33% and autograft only animals had a fusion rate of 63%.

Conclusion: In this model the B2A/G composition appeared to function as a graft enhancer and be more efficacious than autograft alone in this model. B2A peptide has a unique mechanism of action in that although it interacts with receptors for BMP-2, the action is mediated only in the presence of BMP-2 or an osteoinductive event. In this model, the decorticated TP and/or autogenous bone may have provided the necessary signals for B2A. These results suggest that B2A/G should be further investigated to determine mechanistic effects and clinical applications