The Effects of Incremental Maxillomandibular Advancement Surgery on Airway Morphology

Abstract

Obstructive sleep apnea (OSA) is a growing epidemic, affecting up to 7% of the population. Characterized by noctural airway obstruction, OSA is associated with long‐term health effects. To treat this, maxillomandibular advancement surgery (MMA) may be used to expand the dimensions of the pharynx by advancing the maxilla and mandible. Despite positive outcomes, the underlying MMA mechanisms are poorly understood, nor are the ideal advancement parameters defined. The objective of the current study is to investigate the relationship between MMA advancement and resulting airway changes. MMA surgery was performed on five cadaveric specimens. The mandible and maxilla were incrementally advanced using KLS Martin distraction devices. Beginning at baseline, specimens underwent a CT scan at each subsequent 2mm advancement to 14mm (Siemens Medtronic O‐Arm Imaging System; 0.415×0.415×0.833mm,120 kVp, 32 mA, 240 mAs). Segmentation and analysis of changes in airway dimensions were performed in AMIRA (5.3.3, Mercury Computer Systems/3D Viz Group). Linear dimensional changes were measured using a digital ruler at pre‐defined anatomical borders. Superior and inferior boundaries of the airway were defined as the level of the hard palate and base of epiglottis respectively. Length was measured between these boundaries. Anterior/posterior (AP) limits were delineated by a plane perpendicular to the Frankfort horizontal at the base of the tongue and lateral (LAT) dimensions were determined by averaging widths at 25, 50, 75% of AP distance in the same plane. Airway volume was calculated at each 2mm advancement from baseline to 14mm. Normalized results, presented as percent change from baseline, indicate that at 14mm overall mean volumetric increase was 176.5±11.7% mean overall AP increase of 89.5±7.7%, and mean LAT increase was 105.4±8.0%. Maximal incremental changes for volume and AP occurred at 4mm advancement (34.2±23.7% and 21±17%, respectively). In contrast, maximal incremental change for LAT occurred at 10mm (26.5±29.8%). Simultaneously, total length decreased on average, 12.2±0.9% with the maximal decrease at 2mm (‐3.2±1.7%). Incremental morphological changes in the human airway during MMA indicates overall volumetric increase at 12.6% per mm advancement with maximal volumetric enhancement rates happening early in the surgery (17.1%/mm at 4mm). The mechanism of this change is bimodal with maximal rate of AP expansion occurring early (10.5%/mm at 4mm) while later maximal LAT expansion (13.3%/mm at 10mm). Ongoing analysis examines pharyngeal shape change and airflow resistance to better understand functional consequences of MMA.