Controlled Delivery of Low-Dose Bone Morphogenetic Protein-2 Using Heparin-Conjugated Fibrin in the Posterolateral Lumbar Fusion of Rabbits

The heparin‐conjugated fibrin (HCF) system has been developed to deliver bone morphogenetic proteins (BMPs) for a long‐term period and thus enhance bone regeneration. In the present study, we tested the effectiveness of the delivery system for spinal fusion with a very low dose of BMP‐2. A total of 15 rabbits underwent posterolateral lumbar spine, divided into three groups. The control group received only collagen sponges without BMP‐2, another group (BMP‐only group) received collagen sponges loaded with BMP‐2 (10 μg each side), and the last group (BMP/HCF group) received collagen sponges filled with HCF loaded with BMP‐2 (10 μg each side). All animals were euthanized 8 weeks after surgery, and the fusion was assessed by radiographs, manual palpation, computed tomography scan, and mechanical testing. No case in the BMP/HCF group or in the control group achieved solid fusion, while all cases in BMP‐only group showed evidence of solid fusion. BMP/HCF group had significantly lower fusion rate and tensile strength than BMP‐only group at the dose of 10 μg of BMP‐2. The HCF long‐term delivery system with the low dose of BMP‐2 (10 μg) is ineffective for the induction of lumbar posterolateral fusion in the rabbits.