P4. Autologous blood coagulum as a native carrier for rhBMP6 induces new bone formation and posterolateral lumbar spine fusion in rabbits and sheep

Abstract

BACKGROUND CONTEXT RhBMP2 soaked in bovine tendon collagen and synthetic ceramics composite as well as rhBMP7/OP1 lyophilized in bovine bone collagen particles with additive carboxyl-methyl cellulose have been evaluated for posterolateral lumbar fusion (PLF). We investigated rhBMP6 delivered in autologous blood coagulum (ABC), a native carrier (scaffold), with and without allograft bone particles (ALLO) to induce new bone formation and promote posterolateral lumbar spine fusion (PLF) in rabbit and sheep. PURPOSE To evaluate the efficacy of RhBMP6 with autologous blood coagulum (ABC) alone or with ABC and allograft (ALLO) will induce a successful posterolateral spinal fusion in animal models. STUDY DESIGN/SETTING Preclinical evaluation of spine fusion in animal models. PATIENT SAMPLE Multiple experimental groups of rats, rabbits and sheep. OUTCOME MEASURES Radiographic and histologic evaluation for bone formation and spinal fusion. METHODS An autologous bone graft substitute (ABGS) was fabricated by dispersing rhBMP6 in ABC with and without ALLO and evaluated for bone induction in rat subcutaneous implants and to promote bone formation in posterolateral lumbar fusion in preclinical models. The cellular response of bone induction and the quantity and quality of newly formed bone were examined by histology, radiographs, micro-CT analyses at various time intervals. RESULTS ABGS with and without ALLO induced new bone formation in rat implants. ALLO alone induced formation of multinucleated foreign body giant cells (FBGCs). However, ALLO plus ABC decreased the formation of FBGCs. The addition of rhBMP6 to ABC/ALLO, resulted in fewer or no FBGCs. In Rabbits, the groups with ABC alone or with ALLO did not fuse. The 50 micrograms rhBMP6 group only 2 out of 4 animals successfully fused. In the 100 micrograms, 200 micrograms and 400 micrograms rhBMP6 groups all animals successfully fused. In sheep, the groups with ABC or ABC with ALLO failed to fuse. In the rhBMP6 187.5 micro grams/ml group with ABC and instrumentation fusion was achieved in 83% (10/12 animals). In the 187.5 micro grams/ml group with ABC, ALLO and instrumentation, fusion was achieved in 93% (11/12 animals). Bone formation occurred uniformly within ABGS implants where the ALLO was replaced by the newly formed bone via creeping substitution. CONCLUSIONS RhBMP6 with autologous blood coagulum (ABC) alone or with ABC and allograft (ALLO) induced a robust bone formation in posterolateral spinal fusion in preclinical models. FDA DEVICE/DRUG STATUS RhBMP6 (Not approved for this indication).