The Bioadaptive Changes in the Pharyngeal Airway and Hyoid Position Following Mandibular Setback Surgery: A Cephalometric Study

Abstract

Objective: Patients who underwent bilateral sagittal split osteotomy with mandibular setback had been evaluated using lateral cephalograms to identify sites of mechanical obstruction that predispose to airway obstruction. The bioadaptive changes that occur in the peri-airway structures in the post-operative period were evaluated. Methods: The hard and soft tissue landmarks used in cephalometry were used to trace and measure the pharyngeal airway space (PAS) and changes in position of hyoid. Amount of mandibular setback, PAS width, PAS area and changes in the hyoid position were recorded. The difference in pre- and post-operative values measured from cephalometric tracings were analyzed statistically using repeated measure ANOVA. Results: The results demonstrated a significant reduction in PAS width and area corresponding to the decrease in length of mandible after BSSO setback. The decrease in PAS width was found to be 41% of the amount of mandibular setback at 6 months. The mean mandibular setback recorded at 6 months was 8.2 mm. The mean reduction in PAS width registered at 3 and 6 months were 3.8 mm and 3.4 mm (p value 0.001),marginally reclaiming the PAS width at 6 months. The mean reduction in PAS area at 3 and 6 months were 1.6 cm2 and 2.1cm2 (p value 0.009) demonstrating no recovery in the PAS area. The hyoid was displaced posteriorly and inferiorly; the mean displacements in the posterior direction at 3 and 6 months were 2.6 mm and 2 mm (p value 0.013) and inferior direction were 3 mm and 4 mm. Conclusion: Mandibular setback surgery has the potential for narrowing the pharyngeal airway space with a significant reduction in PAS width and area, that could predispose to OSA. The results demonstrate that bioadaptive changes of the hyoid are greater post-surgery and tend to settle in the direction of its pre-surgical position in the anteroposterior plane and drift inferiorly in the supero-inferior plane in an attempt to restore the airway space.