GP2d - How Do Orthognathic Surgical Movements Affect the Postoperative Upper Airway Volume and Maximum Constriction Area?

Due to the intimate association of the upper airway with the maxillomandibular complex, orthognathic surgery may have a significant impact on the patient’s posterior airway volume (PAV). The purpose of this study is to quantify and correlate preoperative and immediate postoperative changes in the volume and maximum constriction area (MCA) in the posterior airway after orthognathic surgical movements.
This retrospective cohort study analyzed both presurgical and postsurgical airway of 39 patients who underwent orthognathic surgery by single surgeon (WDP) from January 9, 2013, and February 9, 2017. The cases were stratified into maxillary advancement, maxillary impaction, mandibular advancement, mandibular setback, genioplasty and a combination of any above movements. All CBCT imaging were acquired at the same facility using iCAT Next Generation Dental with the same protocol. DICOM files were uploaded onto Dolphin 3D. The Dolphin Superimposition Module was used to align the pre- and postoperative CBCT at the cranial base and the lateral cephalometric radiograph generated. Horizontal and vertical measurements of orthognathic movements were obtained via superimposition of pre- and postoperative lateral cephalometric tracing (Figure 1). The Dolphin Sinus/Airway tool was utilized to obtain PAV based on anatomic location: nasopharynx, oropharynx and hypopharynx (Figure 2). Cross-sectional MCA and their locations were obtained with same boundaries used to measure the airway volume (Figure 3).
Linear and volumetric measurements obtained in Dolphin were averaged on Excel. With model-based means, the presence or absence of each surgical movement was analyzed using ANOVA, with all factors included simultaneously in the ANOVA. Pearson correlation coefficients and scatterplots were used to assess the associations between measurements. A 2-sided 5% significance level was used for all tests. Analyses were performed using SAS version 9.
The study included 39 patients: 13 males, 26 females, mean age 30.89.
The greatest MCA percentage change was in maxillary impaction+mandibular advancement+genioplasty with +170.89%. The same group saw the largest increase in total airway volume at +59.18%, largest change in oropharynx sub-volume at +92.03%, and largest horizontal pogonion advancement of +20.50mm.
A decrease in airway volume was seen in maxillary advancement+mandibular setback group at -11.07%, with the least change in MCA at +18.43% and a loss of oropharynx volume at -15.20%.
Largest nasopharynx increase was in maxillary advancement+mandibular setback+genioplasty at +45.54%.
Largest hypopharynx change was in mandibular advancement+genioplasty at +78.60%.
Both mandibular advancement and maxillary impaction+mandibular advancement+genioplasty groups had the largest loss in hypopharynx volume at -20.72% and -19.68% respectively.
The maxillary advancement+mandibular advancement group had 5 of 5 patients with changes to the MCA location. No changes in MCA location were seen in isolated mandibular advancement group. 14 of 39 patients saw a change in MCA location.
Hypopharynx volume, total volume, post op MCA, L1 X, Pog X were significantly higher for genioplasty vs no genioplasty. MCA percent change was significantly lower for mandibular setback than no mandibular setback. Postop MCA showed weak negative association with ANS Y. MCA percent change showed weak positive associations with L1 X and Pog X and weak negative association with PNS Y. There were no associations with nasopharynx, hypopharynx volume percent change. Oropharynx and total percent volume change showed moderate positive associations with L1 X and Pog X.

Positive correlations between L1 X/Pog X and volume/MCA changes indicated mandibular horizontal advancements tend to increase oropharynx/total volume. Genioplasty by itself was associated with increase in hypopharynx/total volume and MCA. Association of L1 X in genioplasty group showed that Class 2 patients in this sample tend to require concurrent genioplasty. MCA has a negative association with clockwise rotation and its location was likely to change with bimaxillary advancement.

Figure 1- Lateral Cephalometric Tracing Superimposition

Figure 2- Posterio Airway Sub Volume Boundaries

Figure 3- Sinus/Airway Mapping for Maximum Constriction Area and Volume