Factors influencing condylar position after the bilateral sagittal split osteotomy fixed with bicortical screws

Multiple articles have discussed condylar position after bilateral sagittal split osteotomy (BSSO). However, previous studies have been limited to two-dimensional evaluation of condylar position. The purpose of this study was to evaluate change in condylar position after a BSSO fixed with bicortical screws using three-dimensional computed tomography to assess the factors that may influence the ultimate position of the condyle after surgery.

Seventeen patients underwent isolated mandibular advancement involving a BSSO with rigid fixation. Reformated axial computed tomography was done 1 week before and 8 weeks after surgery. Movements evaluated included 1) medial-lateral, 2) superior-inferior, 3) anterior-posterior, and 4) condylar angulation. Three separate factors were analyzed to study their effects on the four movements noted: 1) amount of mandibular advancement, 2) amount of proximal segment rotation, and 3) preoperative shape of the mandible. A linear regression analysis was used with statistical significance set at P<.05.

Eight weeks after a BSSO and mandibular advancement, most cases showed displacement of the condyle medially, posteriorly, superiorly, and angled medially. The amount of mandibular advancement did not correlate with medial-lateral change of the condyle. The amount of advancement correlated with the condyle angulation and superior-inferior changes in condyle position. There was no correlation between amount of advancement and medial or anterior-posterior change in condyle position. There also was no correlation between any of the condylar movements and the degree of proximal segment rotation or the shape of the mandible.

There are obvious changes in condyle position after a BSSO. These changes appear to be influenced mainly by factors other than amount of advancement, degree of proximal segment rotation, and shape of the mandible.