Three-dimensional evaluation of proximal segment positional changes and postoperative stability in bilateral sagittal split osteotomy using the novel index Co-B distance.

The aim of this study was to evaluate three-dimensional changes in the mandibular segments following bilateral sagittal split osteotomy, focusing on the positional relationship between the proximal and distal segments and its impact on postoperative stability. Forty-one patients who underwent Le Fort I osteotomy and bilateral sagittal split osteotomy were retrospectively analyzed using computed tomography at preoperative, early postoperative, and 1-year postoperative stages. Segmental superimposition was performed using stable regions of the proximal segment, and the Co-B distance was introduced as a novel three-dimensional index to assess surgical and postoperative changes. In Class III, a significant increase in the Co-B distance (0.650 ± 0.462 mm) was observed postoperatively. Correlation analysis revealed that greater anterior displacement of the Co in Class III (r = 0.49, p = 0.027) and greater lateral (r = 0.69, p = 0.028) and posterior (r = 0.81, p = 0.004) displacements of the Co in Class II were significantly associated with relapse. These findings suggest that the Co-B distance is a valuable indicator for assessing postoperative stability and emphasize the need to prevent lateral displacement of the condyle, especially in Class II cases, to reduce the risk of relapse.