Long-Term Skeletal Relapse Following Mandibular Advancement With Bilateral Sagittal Split Osteotomy

Abstract

The purpose of this retrospective cohort study is to identify the independent risk factors for long-term skeletal relapse following mandibular advancement with bilateral sagittal split osteotomy. Univariate and multivariate linear regression analyses were performed including 9 common risk factors for relapse as independent variables and horizontal/vertical long-term (≥2 years) skeletal relapse as the dependent variable, respectively. Ninety-six patients including 66(68.8%) females, with an average age of 29.7±10.5 years, were analyzed. We found 1.6±1 mm horizontal and 0.9±0.7 mm vertical long-term skeletal relapse over an average follow-up of 3.8±1.8 years after initial mandibular advancement of 8.8±2.4 mm. Multivariate analyses identified age, preoperative mandibular plane angle, bimaxillary surgery, counterclockwise mandibular rotation, and the magnitude of mandibular advancement to be significantly associated with horizontal long-term skeletal relapse. Preoperative mandibular plane angle, counterclockwise mandibular rotation, and the magnitude of mandibular advancement were significantly associated with vertical long-term skeletal relapse. Our results showed that preoperative mandibular plane angle, the magnitude of mandibular advancement, and counterclockwise mandibular rotation of the mandible were independent risk factors for both horizontal and vertical long-term skeletal relapse. Although long-term skeletal relapse cannot be avoided entirely, understanding the independent risk factors and their contributions will optimize treatment planning and long-term stability. The sencond study aims to identify an interaction effect among risk factors for long-term skeletal relapse following mandibular advancement with bilateral sagittal split osteotomy. The study sample consisted of 96 patients who underwent mandibular advancement with bilateral sagittal split osteotomy. Predictor variables analyzed for interaction effect included gender, age, preoperative temporomandibular joint symptoms, mandibular plane angle, single/double jaw surgery, clockwise/counterclockwise mandibular rotation, the magnitude of mandibular advancement, concomitant genioplasty, the type of fixation, and follow-up duration. Multivariable interaction analyses were applied to detect a significant interaction among these risk factors. Stratification analyses and 2-way full factorial interaction analyses were performed to demonstrate how the interaction influenced the associations between covariates and relapse. The interactions of gender and mandibular rotation(p=0.006), as well as the mandibular plane angle and mandibular rotation(p=0.002), were statistically significant with horizontal long-term skeletal relapse. No significant interaction for vertical long-term skeletal relapse was identified. The present study shows that females or patients with a mandibular plane angle ≥ 30° who underwent counterclockwise mandibular rotation were predisposed to greater horizontal long-term skeletal relapse, compared to those who underwent clockwise rotation. Therefore, we recommend judicious use of counterclockwise rotation to minimize the relapse, especially in females and patients with high mandibular plane angle.