Transport distraction osteogenesis using nitinol spring: an exploration in canine mandible

Some experiments in rabbits have presented the potential feasibility of using shape memory alloy spring for continuous distraction osteogenesis. To confirm the effectiveness of such method, we established canine models for the exploratory experiments of transport distraction osteogenesis using nitinol springs. Simple devices, including an internal 60-mm long sinusoid-shaped nitinol springs were used in the study. All dogs needed only one operation. In the operation, osteotomy was performed to create a 40-mm unilateral segmental mandibular body defect and a tooth-bearing transport bone disc. After reconstructive fixation of the remnant mandible, the spring was constricted and anchored across the distraction gap to activate transport distraction immediately. At the second experimental stage, an ePTFE sheet was further fixed to protect the defect and distraction gap before closing the incision. Control dogs underwent the same operation except for anchoring of the spring to examine the spontaneous bone regeneration. Automatic bone transportation, as a gradual slowdown process, was observed under the effect of the spring. The transport disc could get to the opposite side of the defect, or stopped halfway when ePTFE sheet intervened. Mandibular reconstruction was achieved in all these dogs and better in dogs with sheet protection. No integrated bone mass was found in the defect of control dogs. The study further proves that continuous distraction osteogenesis using nitinol springs is a practical technique, although the devices need more improvement for better control of the process of distraction and the quality of regenerated bone.