Evaluation of respiration of the upper airway after orthognathic surgery for mandibular setback movements: Analysis using cephalogram, 3D-CT, and polysomnography

Abstract

Introduction: Mandibular setback surgery leads to posterior movement of the tongue thereby causing a decrease in airway space, which has often been reported as being a predisposing factor for obstructive sleep apnea (OSA). The purpose of this study was to evaluate respiratory changes of upper airway using polysomnography (PSG) after mandibular setback surgery, under consideration of the relationship with postoperative changes of upper airway in 2D using cephalogram (CG) and 3D using computerized tomography (CT).

Patients and methods: In 23 patients with Class III malocclusion, who were anticipated for two-jaw surgery for great mandibular setback movement (≫ 10mm) in the initial paper surgery, PSG for the evaluation of respiratory changes of upper airway was conducted before and 6 months after surgery. CG for the evaluation of 2D and CT for the evaluation of 3D changes of upper airway were taken preoperatively and 6 months postoperatively. The amount of surgical movement was calculated by superimposition of preoperative CG on immediate postoperative CG. Statistical analysis was done for the preoperative and postoperative changes in PSG, CG, and CT. The relationship between postoperative OSA and mandibular setback was statistically evaluated.

Results: The average mandibular setback amount was 10.53 ± 4.58 mm and the average maxillary amount was 2.09 ± 2.77 mm anteriorly at point A. There was a significant decrease in the antero-posterior (1.34 ± 2.80 mm) and medio-distal (1.49 ± 2.99 mm) dimension of the airway at the level of the soft palate in CT (p < 0.05). There was a significant decrease in the anteroposterior dimension of the airway at the level of the tongue base (2.85 ± 5.88 mm) in CT (p < 0.05). The overall airway volume was decreased in 22 patients after the surgery. The average decrease was 21.76 ± 19.68%. This was evident especially in the oropharynx and hypopharynx, showing a decrease of 24.17 ± 18.76% and 17.04 ± 15.80%, respectively. There was a significant decrease (8.97 ± 12.0%) of the overall airway measured in CG (p < 0.01). There was a significant decrease in the area of the oropharynx and hypopharynx by 22.25 ± 26.86% and 14.94 ± 16.17%, respectively (p < 0.001). The nasopharynx showed a significant increase of the area with 12.25 ± 9.87% (p < 0.001). There was statistically no correlation between the development of OSA and the change in 2D area or 3D volume of the airway. While only one patient had polysomnographic value for mild OSA preoperatively, five patients were diagnosed with mild OSA postoperatively. These five patients had a large amount of mandibular setback (15.42 ± 1.20 mm

p<0.001) and clockwise rotation of mandibular distal segment. Postoperative apnea-hypopnea index (AHI) and respiratory disturbance index (RDI) increased significantly (p < 0.05).

Conclusion: Orthognathic surgery for mandibular setback affects the airway volume, and may also cause postoperative OSA. The risk for this phenomenon occurring may be increased in cases involving large amounts of mandibular setback.