Spring-mediated mandibular distraction osteogenesis

Successful performance of distraction osteogenesis requires rigorous patient compliance with a daily activation regimen of a percutaneous screw. Previous clinical studies have found that failure of patient compliance with this regimen is the most common complication leading to technical failure of the distraction process. The authors have developed an internalized spring-mediated device for mandibular distraction osteogenesis that can potentially abrogate the risks associated with patient compliance by allowing for automated distraction across an osteotomy. Twenty adult New Zealand White rabbits underwent unilateral mandibular osteotomy. A segment of nickel-titanium shape memory alloy reinforced at both ends with a pinball was fashioned into an inferiorly based arc and secured to the mandible with stainless steel wire. On postoperative day 12, spring activation commenced by cutting a wire binding the two pinballs to one another. Animals were observed for 6 weeks before they were killed. Radiographic studies and decalcified histologic analysis were performed on extracted mandibles. Temperature- and displacement-dependent properties of the shape memory alloy were also examined. Five animals were excluded from the study due to infection, nonunion, or device failure. A mean distraction of 1.2 mm in the distracted hemimandible relative to the nonoperated hemimandible was found (P <.001, two-tailed paired t test). The maximum distraction achieved in an experimental specimen using the spring distractor was 3.7 mm. There were no other histologic or radiographic differences found between study specimens and specimens subjected to traditional distraction methods. Biomechanical testing of the shape memory alloy revealed a temperature-dependent increase in force at body temperature compared with room temperature and a reduction in force with increased displacement of the spring. This study demonstrates the feasibility of spring-mediated distraction osteogenesis across an osteotomy. As the field of distraction osteogenesis matures, the next level of sophistication in the clinical development of devices will incorporate technology that permits fully internalized and automated distraction to occur.