A Comparison of Mandibular Distraction Vector Effect on Airway and Mandibular Volumes in Pierre Robin Sequence

Background: The goal of mandibular distraction in Pierre Robin Sequence is to maximally expand the oropharyngeal airway. It has been hypothesized that a steep oblique distraction vector may allow greater airway enlargement. This study compares sagittal versus oblique vectors to assess vector correlation with eventual airway volume.

Methods: IRB approval was obtained from two institutions. Micrognathic infants who underwent mandibular distraction with pre- and post-op CT scans were included. Demographic, diagnostic, perioperative data and distraction protocol, including vector relative to the mandibular border , were recorded. Airway and mandibular volumes were measured using Mimics (Leuven, Belgium). Statistics involved two-tailed t-test and Pearson correlation.

Results: 40 CT scans were analyzed. Mean distraction age was 41 days with devices maintained 82 days on average. Vector axis from the inferior mandibular border was ≤ 10 degrees in group 1 (n=10), and > 10 degrees in group 2 (n=10).  Airway and mandibular volumes, minimal airway area, and PAS distance were all significantly increased following distraction. Inter-group analysis showed no difference in airway measurements (no vector correlation to airway). However, mandibular volume was increased in the oblique group, approaching significance (p=0.07), attributable to greater ramus volume (p=0.03), with similar body volumes between groups. Clinically, patients had improved sleep studies post-distraction.

Conclusions: Significant airway enlargement occurs following mandibular distraction. An oblique vector does not result in a greater volumetric airway increase compared to sagittal elongation, but does confer modest increase in ramus volume. Successful clinical outcomes are achieved using both trajectories. Further work will assess vector influence on overall mandibular morphology and presence/persistence of open bite. 

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