P7. Percutaneous delivery of recombinant human bone morphongenetic protein-2 augments fusion in a nicotine impaired rabbit fusion model.

Several experiments have shown that delivery of BMP-2 in a delayed fashion from initial surgery may be superior for optimal bone growth. Studies of posterolateral spinal fusion in rabbits have shown that BMP-2 expression physiologically peaks from 4-6 weeks out from surgery. The hypothesis of this experiment was that delayed delivery of ACS/BMP-2 would augment bone growth in a rabbit spine fusion model. By percutaneously delivering ACS/BMP-2 we would be able to deliver osteoinductive material at an optimal time point away from the typical time of surgery application. To determine if controlled delivery of morselized absorbable collagen sponge (ACS) Rh-BMP2 in a delayed manner postsurgery would allow for increased fusion mass in a rabbit spine fusion model. A nicotine-impaired spinal fusion rabbit model. Sixteen male one-year-old rabbits. Histologic, radiologic (radiographic, CT scans) and palpation examinations were performed to determine fusion status and the volume of bone formed. Sixteen male one-year-old rabbits underwent a posterolateral spinal fusion with iliac crest bone graft at L5-L6 while being given nicotine to prevent spinal fusion as previously published. Eight were controls while 8 had morselized RhBMP-2 (4.2mg) injected at the fusion site at 4 weeks postoperatively. At 12 weeks, the rabbits were sacrificed. Histologic, radiologic (radiographic, CT scans) and palpation examinations were performed to determine fusion status and the volume of bone formed. Hematoxylin and eosin (H&E) stain were used for histology. There were 4 of 8 rabbits in the control cohort with bilateral fusion and 6 of 8 rabbits in the BMP-DDC that had bilateral fusion based on CT scan analysis. A student's t-test was used to compare the CT scan measured volume of bone created between control (CC) and RhBMP-2 delayed delivery cohorts (BMP-DDC). Seven of 8 rabbits in the BMP-DDC and 5 of 8 rabbits in the CC formed definitive fusion with a positive palpation exam, bridging bone between transverse processes on CT scan and an x-ray showing fusion. Histologic analysis revealed new remodeled bone within the BMP-DDC. There was increased average volume of bone formed within the BMP-DDC vs the CC (22.6±13.1 vs 11.1±3.6 cm^3, p=0.04) Our study shows that injectable morselized ACS/RhBMP-2 can create twice as much bone within a nicotine-impaired rabbit spine fusion model when delivered 4 weeks out from time of surgery. This abstract does not discuss or include any applicable devices or drugs. [ABSTRACT FROM AUTHOR]