IN-VIVO EVALUATION OF A RESORBABLE OSTEOINDUCTIVE COMPOSITE AS A GRAFT SUBSTITUTE FOR LUMBAR SPINAL-FUSION

The purpose of this prospective animal study was to evaluate the effic acy of a resorbable coral particulate to serve as a carrier with sever al doses of a bovine-derived osteoinductive bone protein mixture. A pr eviously validated rabbit model for posterolateral intertransverse pro cess lumbar spinal fusion was used. Posterolateral intertransverse pro cess arthrodeses were performed at L5-L6 in 64 adult New Zealand white rabbits. The bone graft substitute evaluated consisted of a Biocoral/ collagen composite with one of four doses (0, 100, 300, or 1,000 mu g) of a bovine-derived osteoinductive bone protein extract (BP). Fusions were assessed at 5 weeks by manual palpation, radiography, histology, and biomechanical testing. Use of the Biocoral/collagen carrier witho ut BP resulted in no solid fusions. Biocoral/collagen with 100 mu g BP resulted in solid fusions in 31% (4 of 13) of the rabbits. Biocoral w ith 300 mu g or 1,000 mu g BP resulted in solid spinal fusion in all r abbits (27 of 27). There were no neurologic complications related to t he growth factor or carrier. Small subcutaneous collections of serous fluid were noted in 26% of the animals in the Ist postoperative week, but resolved without problems by the 5th week. Such seromas may limit the clinical utility of this growth factor-carrier combination. Biocor al/collagen combined with the appropriate dose of bovine-derived osteo inductive bone protein extract was efficacious as a bone graft substit ute for achieving posterolateral lumbar spinal fusion in the rabbit mo del. A dose of 300 mu g BP was determined as the threshold to reliably produce solid spinal fusions.