OBJECTIVE: To assess bone grafting strategies in the chronic caprine tibial defect (CCTD) model. METHODS: Forty-nine female Spanish Boar goats, aged 5±1 years, underwent the CCTD model. Segmental defects were created by excising 5 cm of tibial diaphysis, 9 cm of periosteum, and 10 g of muscle, followed by stabilization with an intramedullary locking nail and an antibiotic polymethylmethacrylate spacer. After four weeks, the spacer was removed. Defects were then grafted with one of five randomly assigned bone grafting strategies: 1) autogenous cancellous bone (ACB) (N=10); 2) mineralized cancellous allograft (MCA) (N=10); 3) MCA+ autologous bone marrow aspirate (BMA) (N=9); 4) MCA+bone morphogenetic protein-2 (BMP-2) (N=10); and 5) MCA+BMP-2+BMA (N=10). The primary outcome was total bone volume (tBV) measured by MicroCT at twelve weeks. Secondary outcomes included MicroCT measurements of radial percent bone volume and moment angle of inertia, and cortical bone bridging assessed by radiographs, ranked from the most to least bony healing by three trained independent reviewers. RESULTS: Animals with MCA+BMP-2 (4542.1 mm3, P=0.026) and MCA+BMP-2+BMA (3633.1 mm3, P=0.006) grafts showed higher median tBV within the central 2.5 cm of the defect compared to animals with MCA+BMA grafts (12.3 mm3). Median tBV within the central 2.5 cm did not differ significantly between animals grafted with ACB (486.8 mm3) and those with MCA+BMP-2 (4542.1 mm3) or MCA+BMA+BMP-2 (3633.1 mm3) grafts. Adding unprocessed BMA to either MCA (MCA: 2.7 mm3 versus MCA+BMA: 12.3 mm3) or MCA+BMP-2 (MCA+BMP-2: 4542.1 mm3 versus MCA+BMA+BMP-2: 3633.1 mm3) did not significantly increase median tBV within the central 2.5 cm. CONCLUSION: In the CCTD model, BMP-2 had a positive effect on tBV, comparable to and trending greater than ACB. This study supports using a composite of MCA+BMP-2 for large segmental bone defects, while the effect of unprocessed BMA requires further evaluation.
Piuzzi et al. (Tue,) studied this question.