Introduction: The changes in mandibular musculature with distraction osteogenesis have not been quantitated. The purpose of this study was to determine the volumetric changes of the medial pterygoid muscle following distraction.

Methods: A retrospective volumetric analysis of the distracted hemimandibles of six human subjects was performed. Four unilateral and two bilateral distraction patients were analyzed. Six sets of CT scans were utilized. Volumetric analysis of the medial pterygoid was performed by calculating the areas of the medial pterygoid muscle on 2D CT slices, and summing the areas to obtain the total volume for the muscle preoperatively and post-distraction.

Results: In four unilateral distraction cases, the average increase of the medial pterygoid muscle volume was 29% on the distracted side of the mandible, and 10% on the contralateral non-distracted side. The average medial pterygoid muscle volume increase in two bilateral distraction cases was 75%.

Conclusions: The medial pterygoid muscle increases in volume with distraction. Furthermore, in unilateral distraction cases, the relative volumetric increase of the medial pterygoid is far greater on the distracted side of the mandible when compared to the non-distracted side of the mandible. This study suggests that muscle is significantly enhanced through distraction osteogenesis.