Magnitude of Horizontal Advancement is Associated With Apnea Hypopnea Index Improvement and Counter-Clockwise Maxillary Rotation After Subcranial Distraction for Syndromic Synostosis.

Subcranial midface distraction is used to treat central midface deficiency in syndromic synostosis. Our aim was to determine which maxillary movements were associated with improvement in measures of obstructive sleep apnea.
This was a retrospective cohort study that reviewed patients with syndromic midface retrusion and documented sleep apnea who underwent subcranial midface distraction via either Le Fort 3 osteotomy or Le Fort 2 osteotomy with zygomatic repositioning. The predictor variables measured on cephalograms were the magnitude and direction of midface and mandibular movements. The primary outcome was the change in the apnea hypopnea index (AHI) from polysomnography before and after surgery. The secondary outcomes were volumes of upper airway containing bone spaces calculated from computed tomography scans. Data analysis included linear regression to estimate the effect of distraction vectors on bone space volumes and AHI changes.
We included 18 patients primarily with Crouzon or Apert syndrome. The magnitude of distraction in a horizontal direction was the most significant factor for AHI improvement and primarily expanded the nasopharyngeal space, but with a smaller impact on the oral cavity space. Clockwise palate rotation was most influenced by a downward direction of distraction, with 24° below horizontal creating a neutral advancement. The greater the magnitude of advancement, the more likely a counterclockwise rotation was observed.
Horizontal magnitude of advancement had the greatest impact on AHI improvement. Vertical lengthening and closure of anterior open bite deformities can be done without compromising airway results as long as total advancement is not compromised. Palate rotation is best controlled by a downward distraction vector, but counterclockwise rotation increases with greater advancement.