Biomechanical assessment of regenerate integrity in irradiated mandibular distraction osteogenesis

Background: The role of mandibular distraction osteogenesis for reconstructing mandibular defects following radiation therapy depends on the quality of attenuated bone healing in the regenerate. This study investigated the regenerate properties after radiation therapy using yield and breaking load. The authors hypothesized that both would be significantly reduced in mandibular distraction osteogenesis following radiation therapy compared with mandibular distraction osteogenesis alone. Methods: Male Sprague-Dawley rats underwent left mandibular fractionated 36-Gy preoperative external beam radiation therapy and then 2 weeks of recovery (n = 7) or no radiation therapy (n = 10) before surgery. External fixators were secured and unilateral osteotomies were created behind the third molar, followed by 4 days of latency and then mandibular distraction osteogenesis: 0.3 mm every 12 hours for 8 days (5.1 mm) and 4 weeks of consolidation. Unoperated controls received no radiation therapy (n = 13). Mandibles were tension tested at 0.5 mm/second to failure, and yield and breaking load were determined. Results: There was a significantly lower breaking load for mandibular distraction osteogenesis following radiation therapy compared with mandibular distraction osteogenesis, alone, but there was no significant difference in yield between the groups. Both groups had significantly lower breaking load and yield when compared with unoperated controls. Conclusions: The lowered breaking load in mandibular distraction osteogenesis following radiation therapy reflects the reduced biomechanical quality of the regenerate, despite evidence of radiographic union. These data show that radiographic union is not an adequate outcome measure for regenerate healing and support the need to define quantitative bone-healing metrics in mandibular distraction osteogenesis following radiation therapy before implementation in head and neck reconstruction.