Repair of a Critical Porcine Tibial Defect by Means of Allograft Revitalization

Background: The authors previously described the generation of vascularized bone in a pig model, using a hemimandibular allograft scaffold, adipose-derived stem cells, recombinant human bone morphogenetic protein-2, and periosteum. This study tests the hypothesis that this allograft revitalization technique is as effective as vascularized autograft for repairing critical bony defects. Methods: Three groups of pigs had 3-cm defects created in their bilateral tibial diaphyses for repair using rigid fixation and one of three modalities. Negative control tibias were repaired with allograft tibia alone. To simulate repair using vascularized autograft, the osteotomized bone in positive control animals was left in situ, with the posterior periosteum intact. Experimental animals' defects were repaired with allograft tibia packed with autologous adipose-derived stem cells and recombinant human bone morphogenetic protein-2, with native periosteum intact. After 8 weeks, unilateral midgraft osteotomies were performed to assess graft healing potential. Serial radiographs and terminal micro-computed tomography and histology enabled evaluation of healing. Results: At week 7 after ostectomy, no negative control tibias had healed (zero of six) whereas most positive control (five of six) and all experimental tibias (six of six) had healed. Unilateral midgraft osteotomies were performed at 8 weeks to assess graft ability to heal. As expected, no negative control tibias (three of three) had radiographic union 7 weeks later. However, all positive control (two of two; p = 0.05) and experimental (three of three; p = 0.01) tibias had healed their repeated osteotomies by this time. Conclusion: Similar to vascularized autograft, revitalized allograft successfully repaired a critical tibial defect, including after refracture, suggesting that this technique may be an alternative to osseous free flaps.