Does Mandibular Distraction Vector Influence Airway Volumes and Outcome?

Abstract

The goal of mandibular distraction in the Pierre-Robin sequence is to maximally expand the oropharyngeal airway. It has been hypothesized that a steep oblique distraction vector might allow greater airway enlargement compared with horizontal distraction. This study compared vector orientation in relation to airway volume and overall clinical outcome. Micrognathic infants who underwent mandibular distraction with sufficient computed tomographic data were retrospectively reviewed. Demographic, diagnostic, perioperative, and distraction data were recorded. Groups were separated based on distraction vector (group 1, horizontal; group 2, oblique). Airway and mandibular volumes were measured using Mimics (Materialise, Leuven, Belgium). Morphologic and outcomes data were analyzed. Statistics involved 2-tailed t test, Pearson correlation, and analysis of covariance (ANCOVA). Mean age at distraction was 40days, with devices maintained for 82days on average. Fifty percent of patients were girls and 65% had cleft palate. Forty computed tomograms were analyzed. Airway (1,234 vs 3,501mm3; P < .01) and mandibular (5,457 vs 11,827mm3; P < .01) volumes, minimal airway area (12.5 vs 63.7mm2; P < .01), and posterior airway space distance (2.3 vs 9.8mm; P= .04) were significantly increased after distraction. Patients also had clinically improved sleep studies after distraction (apnea hypopnea index, 51.3 vs 5.5; P < .01). Vector analysis showed an average of 5.3° and 14.0° in groups 1 and 2, respectively (n= 10 each). Intergroup analysis showed a trend toward increased airway volume in horizontal vectors (548 vs 255% of preoperative volume; P= .058), with slightly longer distraction length (20.3 vs 16.6mm; P= .17). However, ANCOVA regression analysis showed no difference in the relation between vector and length. Other morphologic data and sleep study outcomes (apnea hypopnea index,7.0vs 3.9; P= .09) also were not statistically different between groups. Longer lengths of distraction correlated with narrower anterior mandibular angle and longer mandibular body length. Substantial airway enlargement occurs after mandibular distraction. Final airway volumes were similar between groups regardless of vector, which was confirmed by multivariate ANCOVA regression. The 2 methods achieved airway stabilization, with clinical outcomes similar between the 2 groups.