Defining the Safe Zone for the Low Medial Horizontal Cut in the Sagittal Split Osteotomy.

Purpose: A recent modification of the sagittal split osteotomy (SSO) utilizes a medial cut placed at the level of the mandibular occlusal plane (low) and terminating anterior to the retrolingular fossa (short). The purpose of this work was to evaluate the position of the inferior alveolar nerve (IAN) relative to the medial mandibular ramus cortex in patients undergoing SSO utilizing a low medial cut.

Methods: This was a retrospective, cross-sectional evaluation of patients evaluated at a tertiary-care center for facial skeletal deformities who were candidates for mandibular orthognathic surgery. Patients were included as study subjects if they had medical-grade computed tomography (CT) scans as part of preoperative planning. The measure of interest was the closest distance from the medial cortex to the IAN for a horizontal osteotomy placed at the level of the mandibular occlusal plane, as measured on CT scans using an automated process. Descriptive statistics were computed to identify the proximity of the IAN to the medial cortex as a function of the length of the medial horizontal osteotomy.

Results: Forty-seven patients (94 SSO sites) with a mean age of 18.7 ± 3.3 years were included as study subjects. Twenty-six subjects had a primary diagnosis of congenital craniofacial anomaly; 21 subjects had a primary dentofacial deformity. For medial ramus osteotomy lengths of 7.5 mm, 10 mm, 12.5 mm, 15 mm, and 20 mm, the closest distances to the IANs were 9.8 ± 2.5 mm, 8.3 ± 2.5 mm, 6.5 ± 2.4 mm, 4.8 ± 2.1 mm, and 2.9 ± 1.6 mm, respectively.

Conclusion: When utilizing the low medial cut in the SSO, the IAN is reliably found ≥ 5 mm away from the medial cortex of the ramus when the osteotomy length is < 15 mm.