Predictive Soft Tissue Airway Volume Analysis in Mandibular Distraction: Pushing The Envelope in Surgical Planning for Obstructive Sleep Apnea

Analysis of Upper Airway Flow Dynamics in Robin Sequence Infants Using 4-D Computed Tomography and Computational Fluid Dynamics

Robin Sequence (RS) is a potentially fatal craniofacial condition characterized by undersized jaw, posteriorly displaced tongue, and resultant upper airway obstruction (UAO). Accurate assessment of UAO severity is crucial for management and diagnosis of RS, yet current evaluation modalities have significant limitations and no quantitative measures of airway resistance exist. In this study, we combine 4-dimensional computed tomography and computational fluid dynamics (CFD) to assess, for the first time, UAO severity using fluid dynamic metrics in RS patients. Dramatic intrapopulation differences are found, with the ratio between most and least severe patients in breathing resistance, energy loss, and peak velocity equal to 40:1, 20:1, and 6:1, respectively. Analysis of local airflow dynamics characterized patients as presenting with primary obstructions either at the location of the tongue base, or at the larynx, with tongue base obstructions resulting in a more energetic stenotic jet and greater breathing resistance. Finally, CFD-derived flow metrics are found to correlate with the level of clinical respiratory support. Our results highlight the large intrapopulation variability, both in quantitative metrics of UAO severity (resistance, energy loss, velocity) and in the location and intensity of stenotic jets for RS patients. These results suggest that computed airflow metrics may significantly improve our understanding of UAO and its management in RS.

Virtual Planning and 3D Printing in Contemporary Orthognathic Surgery

Orthognathic surgery is a powerful tool to improve facial balance, form, and function. Virtual planning and three-dimensional printing has improved our ability to visualize complex anatomy, consider various iterations and execute complex movements, and create accurate splints, plates, and cutting guides. This article will outline the distinct advantages of the use of virtual surgical planning over traditional planning, and it will explore the utility of computer-aided design and technology within contemporary orthognathic surgery, including its expanded applications and limitations.

Analysis of Airway and Midface in Crouzon Syndromes

BACKGROUND

Crouzon syndrome is associated with severe respiratory impairment of the upper airway due in part to midfacial dysmorphology. We calculated the distinctive nasal diameter and pharyngeal airway volume in patients with Crouzon syndrome and compared them with age-matched control subjects.

METHODS

Children with computed tomography scans in the absence of surgical intervention were included. Computed tomography scans were digitized and manipulated using Surgicase CMF (Materialise). Craniometric data relating to the midface and airway were collected. For all linear measurements, mean percent increases or decreases were calculated relative to the size of control subjects, and volumetric assessment of the airway was tabulated. Statistical analysis was performed using t test.

RESULTS

Twenty-six computed tomography scans were included (control n = 17, Crouzon n = 9). All children were in early mixed dentition. Pharyngeal airway volume was decreased in patients with Crouzon syndrome relative to control subjects by 46% (P = 0.003). The distance from the posterior tongue to the posterior pharyngeal wall decreased 31% when comparing the Crouzon group versus the control (P = 0.04).

CONCLUSIONS

Three-dimensional analysis revealed notably decreased pharyngeal and nasal airway volumes in patients with Crouzon syndrome, but nasal bone tissue and soft tissue measurements showed very little change between patients and control subjects.

Airway Morphological Changes in Pierre Robin Sequence: A Retrospective Study

Objective:

To investigate airway morphology changes in patients with Pierre Robin sequence (PRS) pre–/post–mandibular distraction osteogenesis (MDO) and to compare morphologic changes to age-matched controls.

Design:

Retrospective case–control study.

Setting:

Urban, academic, tertiary medical center.

Patients, Participants:

Fifteen patients with PRS after MDO to relieve upper airway obstruction (UAO) (2008-2018); age-matched controls for post-MDO patients.

Interventions:

Mandibular distraction osteogenesis, curvilinear internal mandibular distractors.

Main Outcome Measures:

(1) Physiologic improvement after MDO (apnea–hypopnea index; minimum oxygen saturation); (2) airway size (volume, surface area, length, mean/minimum cross-sectional area), shape (lateral:anterior–posterior ratio, cross-sectional area ratios, uniformity, sphericity), and changes with MDO; and (3) post-MDO airway size, shape versus age-matched controls.

Results:

Airway size increased after MDO (volume, P = .01; surface area, P = .02; length, P = .01), as did cross-sectional area (mean, P = .02; minimum, P = .02; minimum retropalatal, P = .05, mid-retroglossal, P = .02). Post-MDO PRS airways were larger than controls (volume, P < .01; surface area, P < .01; length, P < .01, cross-sectional area, P = .03). Airway shape remained nonuniform and flat post-MDO; control airways were round. Two syndromic patients required repeat MDO and had subphysiologic post-MDO airway cross-sectional area. Post-MDO PRS patients with supraphysiologic cross-sectional area along the entire airway had no UAO recurrence.

Conclusions:

In this small, heterogenous patient sample, MDO increases airway size, may preferentially affect the retropalatal airway, and often results in supraphysiologic airway dimensions. These retropalatal changes may be important in relieving severe UAO in patients with PRS. Generalizability of our results is limited by small cohort size and patient heterogeneity.

Airway Volume Simulation in Virtual Mandibular Distraction: A Cohort Study

BACKGROUND

The authors investigated the accuracy of virtual surgical planning in predicting airway volume changes after mandibular distraction in patients with Pierre Robin sequence and associated tongue-based airway obstruction.

METHODS

The authors completed a single-institution retrospective review of patients for whom virtual surgical planning was used during mandibular distraction osteogenesis for treatment of tongue-based airway obstruction. Preoperative airway volume, virtual surgical planning-predicted airway volume, and postoperative airway volume were calculated from three-dimensional computed tomographic scans using industry software. A blinded institutional radiologist also calculated pre- and post-operative airway volumes. Pre- and post-operative polysomnography was used to titrate the endpoint of mandibular lengthening.

RESULTS

Eleven patients were included in the study. Mean apnea-hypopnea index (5.42 ± 4.53 versus 44.96 ± 20.57; p < 0.001) and mean nadir oxygen saturation (70.3 ± 9.72 percent versus 82.9 ± 9.62 percent; p = 0.003) improved with mandibular distraction. There was moderate correlation between predicted and actual mandibular distraction lengths (R = 0.65; p = 0.003). There was a strong correlation between predicted and industry-calculated actual post-distraction airway volume (R = 0.99; p < 0.001). There was no significant correlation between actual mandibular distraction length and industry-calculated actual post-distraction airway volume for the entire cohort (R = 0.05; p = 0.49), but correlation approached significance by institutional calculations. No significant correlation existed between industry and institutional-calculated percentage change in post-distraction airway volume (R = 0.06; p = 0.57).

CONCLUSIONS

Predictive airway volume calculation may be an effective adjunct to determine anatomic endpoint of mandibular distraction but small sample size, operator and software variability, and patient airway morphology may confound firm conclusions. Further studies are warranted.