Mandibular Foramen Position Predicts Inferior Alveolar Nerve Location After Sagittal Split Osteotomy With a Low Medial Cut

To evaluate whether the distance between the mandibular occlusal plane and mandibular foramen predicts inferior alveolar nerve (IAN) position after the sagittal split osteotomy (SSO) when using a low medial horizontal osteotomy (Posnick's modification).This was a retrospective cohort study of patients undergoing bilateral SSOs with the medial osteotomy placed at the level of the mandibular occlusal plane. The primary predictor variable was the vertical distance between the mandibular foramen and mandibular occlusal plane. The primary outcome was IAN position after SSO: contained within the proximal segment or freely entering the distal segment. Secondary predictor variables were age, gender, primary diagnosis, and type of surgery. Descriptive, bivariate, and regression statistics were computed.Thirty-one patients underwent 62 SSOs using a low medial cut; the sample's mean age was 19.6 ± 3.0 years, and 16 subjects were female. Twenty-three subjects had a primary diagnosis of craniofacial anomaly, and 26 subjects underwent bimaxillary surgery. The IAN was contained within the proximal segment in 28 SSOs (45.2%). The distance between the mandibular occlusal plane and mandibular foramen was greater in SSOs where the nerve was contained within the proximal segment (6.9 ± 2.5 mm) versus freely entering the distal segment (4.5 ± 2.7 mm, P .001). A receiver-operator characteristic curve identified a threshold distance of greater than 5 mm as predictive of the IAN being contained within the proximal segment (sensitivity, 0.89; specificity, 0.85; area under the curve, 0.84; P .001). When the mandibular foramen was greater than 5 mm above the mandibular occlusal plane, there was an increased odds of the IAN being contained within the proximal segment (odds ratio, 48.3; 95% confidence interval, 10.5, 222.8; P .001).The distance between the mandibular occlusal plane and mandibular foramen predicts the position of the IAN after SSO when using a low medial horizontal osteotomy.