Does the sheep mandible relapse following lengthening by distraction osteogenesis?

Aim: Distraction osteogenesis is a technique used to lengthen the shortened mandible. However, the long term stability of the distracted mandibular bo ne is not known. The aim of this study was to assess if the sheep mandible relapses following lengthening, and to assess the quality of distracted bon e up to 1 year post lengthening. Methods: Twenty-four sheep had bilateral e xternal mandibular distracters applied, with three sheep as controls. Titan ium marker screws were positioned both proximal and distal to the distracti on zone in all sheep. Following a 5 day latency period, the interdental gap was distracted 1 mm/day for 20 days, with a subsequent 20 day consolidatio n period. Ante-mortem serial X-rays were used to assess for relapse by meas uring the distance between the screws. The animals were sacrificed at eithe r 3, 6, 9 or 12 months post-distraction. At post mortem, the distance betwe en the screws was re-measured. The distracted bone was assessed mechanicall y and histologically. Results: The mean mandibular lengthening obtained was 13.2 mm. There was no relapse of the mandible over 12 months. The distract ed bone had attained the strength and stiffness of undistracted bone by 6 m onths post-distraction (p<0.05). Histological evaluation revealed significa nt amounts of lamellar bone by 6 months post-distraction. Conclusions: No r elapse occurred for 12 months post distraction lengthening. The bone formed following distraction was stable and of good quality. These findings lend support to the use of distraction osteogenesis in clinical practice. (C) 20 00 European Association for Cranio-Maxillofacial Surgery.