Session IX - Basic Science
Evaluation of INFUSE Bone Graft in a Canine Critical Size Defect: Effect of Sponge Placement on Healing
Purpose: Critical factors in healing large traumatic bony defects using bone morphogenetic proteins (BMPs) include maintenance of defect space and a source of cells. This study evaluated the healing potential of BMP-2 soaked onto an absorbable collagen sponge (rhBMP-2/ACS, INFUSE Bone Graft, Medtronic Sofamor Danek, Memphis, TN) combined with morcellized allograft bone compared to allograft or autograft bone alone. The study also determined whether the rhBMP-2/ACS position relative to the soft-tissue cell source affected healing.
Methods: 21 adult male dogs received bilateral 2.5-cm critical size segmental defects in the midulna. Each defect received the equivalent of 3 cc of graft material: morcellized cancellous allograft, autograft, or mixtures of allograft + rhBMP-2/ACS. The sponge was morcellized and uniformly mixed with allograft, rolled around the allograft, or folded and placed over the allograft adjacent to the muscular soft-tissue cell source. Two rhBMP-2 concentrations were investigatedclinical (1.5 mg/ml) and canine (0.43 mg/ml). Healing was assessed over a 12-week study period using radiographic, biomechanical, and histologic techniques.
Results: The mixture of rhBMP-2/ACS with allograft regardless of concentration or sponge placement resulted in complete radiographic, mechanical, and histologic healing superior to that demonstrated with autograft bone. By 4 weeks all 30 defects treated with the rhBMP 2/ACS + allograft mixtures were completely bridged radiographically with new bone. By 12 weeks, 5 of 6 autograft-treated defects were radiographically bridged and had a mean torsional strength that was 48% of intact ulna strength. The BMP-2 treated defects had a mean torsional strength that was 97% of intact ulna strength. The canine concentration resulted in a higher mean torsional strength (118%) than that of the clinical concentration (81%). Histologically, significant amounts of new bone and extensive callus formation were observed for the rhBMP-2/ACS treated defects regardless of rhBMP-2 concentration and sponge placement. None of the defects treated with allograft bone were healed at 12 weeks postoperatively.
Conclusion/ Significance: rhBMP-2/ACS combined with allograft bone healed critical size defects better than autograft bone and provides an effective means for grafting large bony defects in trauma and reconstructive procedures.