Evaluation of inferior alveolar nerve function during distraction osteogenesis in the dog

Purpose: A series of electrophysiologic studies were performed in a canine model to evaluate inferior alveolar nerve (IAN) function during distraction osteogenesis of the mandible. Materials and Methods: Fourteen dogs, including two controls, were used in the study. Twelve dogs underwent a IO-mm bilateral mandibular lengthening w ith an intraoral bone-borne appliance and midbody osteotomy. By using senso ry nerve action potentials, LAN function was assessed before and immediatel y after surgery, before and at the completion of distraction, and before ne cropsy after 4, 6, or 8 weeks of fixation. Results: Twelve of the 24 nerves showed a complete loss of evoked potential after surgery without recovery at any point throughout the study. Acute ne rve injury caused by either the osteotomy or screw encroachment was identif ied at necropsy. The other 12 nerves showed reproducible responses after su rgery. Eight of these nerves had significant amplitude attenuation of the e voked potentials, which was identified at necropsy as a result of acute inj ury. The remaining four nerves did not show significant evoked potential ab normalities and appeared to be grossly normal at necropsy. During distracti on, the amplitude of evoked potentials in all 12 nerves remained at the pos toperative level, whereas latency showed a significant delay. In 7 of these 12 nerves, various degrees of evoked potential recovery were identified at the completion of the study. Conclusions: The high incidence of acute IAN injury in the current study wa s primarily related to device construction and osteotomy technique. If acut e nerve injury is avoided at surgery, distraction osteogenesis with 10 mm m andibular lengthening appears to produce minimal deleterious effect on LAN function.