upper airway length decreases after maxillomandibular advancement in patients with obstructive sleep...

J Oral Maxillofac Surg69:677-686, 2011

Three-Dimensional ComputedTomographic Airway Analysis of PatientsWith Obstructive Sleep Apnea Treated by

Maxillomandibular AdvancementZachary Abramson, DMD,*

Srinivas M. Susarla, DMD, MD, MPH,† Matthew Lawler, BA,‡Carl Bouchard, DMD, MSc, FRCD,§ Maria Troulis, DDS, MSc,!

and Leonard B. Kaban, DMD, MD¶

Purpose: To evaluate changes in airway size and shape in patients with obstructive sleep apnea (OSA)after maxillomandibular advancement (MMA) and genial tubercle advancement (GTA).

Materials and Methods: This was a retrospective cohort study, enrolling a sample of adults withpolysomnography-confirmed OSA who underwent MMA ! GTA. All subjects who had preoperative andpostoperative 3-dimensional computed tomography (CT) scans to evaluate changes in airway size andshape after MMA ! GTA were included. Preoperative and postoperative sleep- and breathing-relatedsymptoms were recorded. Descriptive and bivariate statistics were computed. For all analyses, P " .05was considered statistically significant.

Results: During the study period, 13 patients underwent MMA ! GTA, of whom 11 (84.6%) met theinclusion criteria. There were 9 men and 2 women with a mean age of 39 years. The mean body massindex was 26.3; mean respiratory disturbance index (RDI), 48.8; and mean lowest oxygen saturation,80.5%. After MMA ! GTA, there were significant increases in lateral and anteroposterior airway diameters(P " .01), volume (P # .02), surface area (P " .01), and cross-sectional areas at multiple sites (P " .04).Airway length decreased (P " .01) and airway shape (P # .04) became more uniform. The mean changein RDI was –60%.

Conclusions: Results of this preliminary study indicate that MMA ! GTA appears to produce significantchanges in airway size and shape that correlate with a decrease in RDI.© 2011 American Association of Oral and Maxillofacial SurgeonsJ Oral Maxillofac Surg 69:677-686, 2011

Traditional 2-dimensional (2D) analyses of lateralcephalograms have been used to evaluate airway pa-rameters in patients undergoing treatment for ob-

structive sleep apnea (OSA).1-3 More recently, ad-vances in 3-dimensional (3D) imaging and surgicaltechnique have stimulated an interest in computed

Received from the Department of Oral and Maxillofacial Surgery,

Massachusetts General Hospital and Harvard School of Dental Med-

icine, Boston, MA.

*Resident; Former AO/Synthes/MGH Student Research Fellow in

Pediatric Craniomaxillofacial Surgery.

†Resident.

‡AO/Synthes/MGH Student Research Fellow in Pediatric Cranio-

maxillofacial Surgery.

§AO-ASIF/Synthes Fellow in Pediatric Craniomaxillofacial Surgery.

!Associate Professor.

¶W.C. Guralnick Professor and Chairman.

This manuscript was presented in part at the American Associ-

ation of Oral and Maxillofacial Surgeons Annual Meeting, Toronto,

Ontario, Canada, October 16, 2009.

This study was supported by the Hanson Foundation, the AO/

Synthes Research Fellowship in Pediatric Oral and Maxillofacial

Surgery (Z.A., M.L.), the Oral and Maxillofacial Surgery Foundation

Fellowship in Clinical Investigation (S.M.S.), and the Massachusetts

General Hospital Department of Oral and Maxillofacial Surgery

Education and Research Fund (Z.R.A., S.M.S., M.L.) and Center for

Applied Clinical Investigation (S.M.S.).

Address correspondence and reprint requests to Dr Kaban: De-

partment of Oral and Maxillofacial Surgery, Massachusetts General

Hospital, 55 Fruit St, WRN 1201, Boston, MA 02114; e-mail:

[email protected]

© 2011 American Association of Oral and Maxillofacial Surgeons

0278-2391/11/6903-0011$36.00/0

doi:10.1016/j.joms.2010.11.037

677

mailto:[email protected]

tomography (CT)–based 3D airway analysis for diag-nosis, treatment planning, and outcomes assessmentin patients with craniomaxillofacial deformities andOSA.4,5 An association between 3D upper airway anat-omy and the presence and severity of OSA has beenreported.4-10 Airway-altering procedures, such asmaxillomandibular advancement (MMA), with orwithout genial tubercle advancement (GTA), havebeen shown to improve the symptoms of patientswith OSA.11-14 However, the mechanism by whichMMA improves the obstructed airway is not welldocumented.15-17

Three-dimensional CT measurements of airway sizeand shape in asymptomatic men and women by agehave been reported and compared with data frompatients with OSA.18 Airway length above the mean isassociated with the presence of OSA.19 In addition,the combination of a long airway with a decreasedretroglossal lateral-to-anteroposterior ratio has beenfound to correlate with the severity of OSA.20 Theextent to which orthognathic surgery alters these andother 3D airway parameters remains uncertain, be-cause there have been few reports correlatingchanges in 3D airway size and shape with MMA !GTA.16,17

The purpose of this study was to documentchanges in airway anatomy, as measured on 3D CTscans, after MMA ! GTA. The specific aims were 1) toevaluate 3D changes in airway size and shape afterMMA ! GTA, 2) to compare preoperative and post-operative airway anatomy of OSA patients with age-matched asymptomatic control subjects, and 3) tocorrelate airway changes with changes in symptoms.We hypothesized that subjective and objective im-provement in OSA patients would correlate with nor-malization of airway size and shape after MMA !GTA.

Materials and MethodsPATIENTS AND STUDY DESIGNThis was a retrospective cohort study of patients

with OSA treated by MMA ! GTA at the Departmentof Oral and Maxillofacial Surgery, Massachusetts Gen-eral Hospital (Boston, MA), over a 29-month period(August 2007 to December 2009). This study wasapproved by the Partners Institutional Review Board(Protocol #2006P00811). Subjects were included if 1)the diagnosis of OSA was confirmed by overnightpolysomnogram and 2) there were pretreatment andpost-treatment 3D CT scans from the hard palate tothe base of the epiglottis. Patients who did not havepreoperative polysomnograms, had inadequate docu-mentation, or were lacking preoperative or postoper-ative CT scans were excluded.

To assess normalization of airway anatomy, postop-erative airway measures were compared with a stan-dardized set of airway measurements from CT scansof patients without OSA or any sleep-related symp-toms, as reported in a previous study.18

SURGICAL PROCEDUREMMA ! GTA was performed with the patient under

nasoendotracheal anesthesia. Dissection and cortico-tomies for bilateral sagittal split osteotomies wereperformed on both sides of the mandible. Le Fort Iosteotomy was subsequently carried out to mobilizeand advance the maxilla to the planned position, byuse of a fabricated intermediate splint. Wire maxillo-mandibular fixation was applied, and the maxilla wasrigidly fixed at the piriform rims and zygomaticomax-illary buttresses with Synthes titanium plates andscrews (Synthes CMF, West Chester, PA). Maxilloman-dibular fixation was released, the intermediate occlu-sion was verified, and the mandible was then split,mobilized, advanced, and rigidly fixed with either 3positional screws or plates and monocortical screws.GTA was carried out via an anterior sulcus incision. Arectangular block of mandibular symphysis, locatedbetween the canines and containing the lingual at-tachment of the genioglossus muscle, was osteoto-mized, advanced, and rotated 90°.21 The block wassubsequently fixed superiorly and inferiorly to thesurrounding symphyseal bone by use of titaniumscrews. Patients were not placed in maxillomandibu-lar fixation postoperatively. After the procedure, theywere monitored overnight in the postanesthesia careunit or surgical intensive care unit for significant de-saturation or other airway emergencies.

IMAGE ACQUISITIONThe methodology for preoperative and postopera-

tive image acquisition and analysis described in thisarticle has been previously published by ourgroup.18,20,22 In brief, maxillofacial noncontrast CTscans (GE Lightspeed; GE Medical Systems, Milwau-kee, WI) (120 kV and 80 mA) consisting of 2.5-mmaxial tomograms, with reconstructions in the coronaland sagittal planes, were used for this study. Thesestudy parameters were chosen to ensure accuracy ofskeletal and soft tissue images.23 Patients were supineand were instructed to remain still, not to swallow,and to hold their breath at the end of exhalation. Allscans were completed in the craniocaudal direction.

Standardized digital lateral cephalograms were ob-tained as part of preoperative and postoperativeworkup by use of Planmeca Dimax 2 Ceph (Plan-meca, Helsinki, Finland). The x-ray settings were 62 to66 kilovolts (peak) (based on gender and race), 9 to12 mA (based on gender and race), and source-sensordistance of 50 to 60 cm (1.13$ magnification). Radio-

678 CT AIRWAY ANALYSIS AND OSA

graphs were taken with the patient standing in thenatural head position and stabilized by a head holderand ear rods. The mandible was positioned in centricrelation and the lips relaxed. Patients were instructedto place the tongue against the incisor teeth and notto swallow. A reference line of 50 mm was used tocalibrate measurements for each image.

IMAGE ANALYSIS

Scans were imported into a CT-analyzing computersoftware program (3-D Slicer [available as freeware athttp://slicer.org]), developed at the Harvard SurgicalPlanning Laboratory (Brigham and Women’s Hospital,Boston, MA). Digital 3D model reconstructions of theairways were made (Fig 1).23 The superior airwayboundary was defined at the level of the hard palateand the inferior boundary at the base of the epiglottis,consistent with methods described in the litera-ture.16,23 The superior boundary was the axial slicethat best visualized the posterior nasal spine. Theinferior boundary was the axial slice that intersectedthe inflection point made by the base of the epiglottisand the anterior pharyngeal wall. The lateral and pos-terior boundaries of the model consisted of the pha-ryngeal walls and the anterior boundary, the anteriorwall of the pharynx, the base of the tongue, and thesoft palate.

Cephalometric digital radiographs were loaded intothe image-analyzing software program Dolphin (ver-sion 10.0.00.50; Dolphin Imaging & Management So-lutions, Chatsworth, CA), and 2D linear measure-ments of maxillary and mandibular advancementwere made.

AIRWAY PARAMETERSOnce 3D digital models were constructed, the fol-

lowing airway parameters were measured or calcu-lated: volume, surface area, length, average cross-sectional area (CSA), minimum retroglossal area,minimum retropalatal area, minimum CSA, retroglos-sal anteroposterior dimension (AP), retroglossal lat-eral dimension (LAT), LAT/AP ratio, minimum retro-palatal area/retroglossal area, uniformity, and sphericity(%). The reliability and precision of these measure-ments have been documented in a previous investi-gation and were all shown to be highly precise, withintraclass correlation coefficients greater than 0.9.23

CT skeletal landmarks were also identified in themidsagittal plane: genial tubercle and hyoid bone. Thedistance between genial tubercle and hyoid bone wasmeasured. For all OSA patients, height (in centime-ters) was recorded and used to compute a correctedairway length (length/height) (Table 1).22

MEASUREMENT OF MAGNITUDEOF ADVANCEMENTThe magnitude of maxillary and mandibular ad-

vancement was measured in accordance with meth-ods previously described.24,25 For maxillary advance-ment and position, the true horizontal line wasdefined as the sella-nasion line rotated 6° clockwisefrom point S (sella). The posterior vertical referenceline was a line passing through S and perpendicular tothe true horizontal. The anterior vertical referenceline was a line passing through point A and perpen-dicular to the true horizontal. The distance betweenthe anterior and posterior vertical reference lines wasmeasured before and after MMA. The difference be-

FIGURE 1. Three-dimensional CT airway parameters. A, The region of interest extends from the hard palate (HP) to the base of the epiglottis(EB). The retropalatal region extends from the HP to the inferior aspect of the soft palate (SP). The retroglossal region extends from the SP tothe EB, and the retroglossal space (RG) is defined as halfway between SP and EB. B, Length is measured from HP to EB in the midsagittalplane. Volume and surface area are calculated from the 3D digital model. C, On axial cross sections of the airway, 2D areas and lineardimensions can be measured. Within the retroglossal space, the lateral and AP dimensions are measured. CSAs are measured in the axialplane, and the lowest values in the retroglossal and retropalatal regions are recorded. (Modified with permission from Abramson Z, SusarlaS, Troulis M, Kaban LB: Age-related changes of the upper airway assessed by 3-dimensional computed tomography. J Craniofac Surg20:657, 2009 [suppl 1].)Abramson et al. CT Airway Analysis and OSA. J Oral Maxillofac Surg 2011.

ABRAMSON ET AL 679

http://slicer.org

tween the preoperative and postoperative distanceswas the magnitude of maxillary advancement (in mil-limeters). A similar process was used to measure man-dibular advancement, by use of point B.

DEFINITION OF ABNORMALFor the purposes of this study, any airway measure-

ment deviating from the norm that would be ex-pected to increase upper airway resistance was con-sidered pathologic (eg, smaller CSA, longer airway,less uniform airway or decreased posterior airwayspace [PAS], and increased hyoid to mandibular planedistance).

SLEEP- AND BREATHING-RELATED DATASleep- and breathing-related data were collected

preoperatively and postoperatively. Preoperatively,the respiratory disturbance index (RDI), lowest oxy-

hemoglobin saturation, need for continuous positiveairway pressure (CPAP) during sleep, and symptoms(ie, snoring, daytime somnolence, fatigue, difficultybreathing, attention deficit, poor memory, headaches,and falling asleep while driving) were recorded. Post-operatively, the need for CPAP during sleep and thesame sleep- and breathing-related symptoms were re-corded.

STATISTICAL ANALYSISData were entered into a statistical database (SPSS

software, version 13.0; SPSS, Chicago, IL) over thecourse of the study. Descriptive statistics were com-puted to provide an overview of the study population.Bivariate statistics were computed to compare preop-erative and postoperative subjective and objectivedata. Given the small sample size and lack of con-firmed normality within the data set, nonparametric

Table 1. DEFINITION OF AIRWAY PARAMETERS

Airway Parameter Symbol Type Unit Definition

CT: SizeVolume VOL 3D mL Volume of airway from base of epiglottis and

hard palateSurface area SA 2D cm2 Surface area of airwayLength L 1D mm Length from hard palate to base of epiglottisMean cross-sectional area avgCSA 2D mm2 Mean CSA, equal to VOL/LengthMinimum retropalatal area RP 2D mm2 Minimum CSA of retropalatal airway (from

inferior aspect of soft palate to level of hardpalate)

Minimum retroglossal area RG 2D mm2 Minimum CSA of retroglossal airway (from baseof epiglottis to inferior aspect of soft palate)

Minimum cross-sectional area minCSA 2D mm2 Lowest value among RG and RP, lowest CSA ofairway

Lateral dimension of retroglossalairway

LAT 1D mm Lateral dimension of cross section of airway inmiddle of retroglossal area (between base ofepiglottis and inferior aspect of soft palate

Anteroposterior dimension ofretroglossal airway

AP 1D mm Anteroposterior dimension of cross section ofairway in middle of retroglossal area (betweenbase of epiglottis and inferior aspect of softpalate)

Genial tubercle to hyoid bonedistance*

GH 1D mm Distance from genial tubercle to hyoid bone inmidsagittal plane.

CT: ShapeRatio of lateral to anteroposterior

dimensionsLAT/AP Ratio NA Ratio of AP and lateral dimensions

Ratio of minimum retropalatal andretroglossal areas

RP/RG Ratio NA Ratio of RP and RG areas

Airway uniformity* U Ratio NA Airway uniformity, defined as minimum CSAdivided by mean CSA

Sphericity* % Formula NA Mathematical measure of sphericity (how roundan object is). A flat object has a sphericity of0, and a sphere has a sphericity of 1 sphericity(%) # [!1/3(6 $ VOL)2/3]/SA

Abbreviations: 1D, 1-dimensional; NA, not available.NOTE. Modified from Abramson Z, Susarla S, Troulis M, Kaban LB: Age-related changes of the upper airway assessed by

3-dimensional computed tomography. J Craniofac Surg 20:657, 2009 (suppl 1).*Novel parameters not found in the literature.

Abramson et al. CT Airway Analysis and OSA. J Oral Maxillofac Surg 2011.


methods were used. Pearson correlations were com-puted to evaluate associations between the magni-tude of maxillary or mandibular advancement andchanges in CT airway measurements. For all analyses,P " .05 was considered statistically significant.

ResultsFrom 2004 through 2009, 112 patients were eval-

uated for OSA. Twenty-eight patients were treatedwith MMA ! GTA. On the basis of preliminary inves-tigations using 3D CT imaging to aid the diagnosis andmanagement of OSA,18-20,22 we began obtaining pre-operative and postoperative maxillofacial CT scansfor all adults with OSA in August of 2007.

From August 2007 through December 2009, 13patients underwent MMA for treatment of OSA, ofwhich 11 (84.6%) met the inclusion criteria for thestudy. One patient was missing a postoperative CTscan, and one patient had a postoperative CT scanthat was not amenable for analysis because of move-ment artifact. The sample’s mean age was 38.9 & 12.9years (range, 21-55 years), 9 patients (81%) were men,and the mean body mass index was 28.7 & 5.9 kg/m2

(range, 21.5-41.0 kg/m2). All patients complained ofdaytime sleepiness and were unable to tolerate CPAP/

bilevel positive airway pressure. The mean RDI was48.8 & 27.1 events per hour (range, 16.0-111.0 eventsper hour); the mean oxygen saturation nadir was80.5% & 11.4% (range, 60.0%-93.0%). The meanamount of maxillary and mandibular advancementwas 9.2 & 2.7 mm (range, 2.0-12.4 mm) and 10.1 &2.7 mm (range, 4.1-14.5 mm), respectively. Descrip-tive parameters are listed for each patient in Table 2.

Table 3 summarizes the changes in airway size andshape, as assessed by 3D CT. Volume; surface area;average, retropalatal, retroglossal, and minimal CSA;retroglossal lateral and anteroposterior diameters; andgenial tubercle-hyoid distance increased as a result ofMMA ! GTA (P " .04). Postoperatively, airways werealso more uniform (P # .04). Airway length was theonly parameter that became statistically significantlysmaller as a result of MMA ! GTA (P " .01).

A comparison of CT airway parameters betweensubjects with OSA, before and after MMA ! GTA, andasymptomatic adult control subjects without OSA isshown in Table 4. Compared with normal adult con-trol subjects, OSA subjects had longer, narrower, andless uniform airways before MMA ! GTA (P " .01).After MMA ! GTA, volume, surface area, averageCSA, retropalatal CSA, minimal CSA, retroglossal lat-eral diameter, and genial tubercle–to–hyoid distance

Table 2. DESCRIPTIVE DATA FOR STUDY POPULATION (N ! 11 SUBJECTS)

Patient

Demographic Data Preoperative Data Polysomnographic DataSurgical

Advancement

GenderAge(yr)

BodyMassIndex Symptoms Indications

RDI (Events perHour)

SpO2 min(%)

Maxilla(mm)

Mandible(mm)

1 Male 37 26.7 Daytime sleepiness, snoring BiPAP intolerance 51 93 10.67 11.952 Male 31 23.1 Daytime sleepiness, poor

sleepCPAP intolerance 31 85 8.19 10.14

3 Female 21 21.5 Daytime sleepiness,difficulty concentrating

CPAP intolerance 16 89 9.11 10.58

4 Male 49 30 Daytime sleepiness, snoring,sleeping while driving

BiPAP intolerance 54.8 73 10.11 11.96

5 Female 21 26 Daytime sleepiness, snoring,headaches


6 Male 36 26 Daytime sleepiness, snoring,sleeping while driving,poor concentration

CPAP ineffective 111 74 10.41 12.19

7 Male 31 28.9 Daytime sleepiness, fatigue,poor memory


8 Male 37 28.1 Daytime sleepiness CPAP intolerance 51 87 10.14 7.799 Male 55 41 Daytime sleepiness NA 60 1.99 4.06

10 Male 55 26.6 Daytime sleepiness, sleepingwhile driving, poorconcentration


11 Male 55 38 Daytime sleepiness, snoring,fatigue, difficultybreathing

Oral appliancefailure

28 65 10.58 10.13

Abbreviations: BiPAP, bilevel positive airway pressure; NA, not available; SpO2 min, lowest hemoglobin-oxygen saturation.


ABRAMSON ET AL 681

all increased beyond the non-OSA values (P " .04).Postoperative airway length in OSA subjects, thoughsignificantly decreased relative to the preoperativevalue, still remained significantly greater than in con-trol subjects (P " .01).

Subjective and objective assessments are listed inTable 5. The majority of patients (10 of 11) reportedno symptoms after MMA ! GTA. One patient re-ported some mild snoring. The postoperative RDI at 3to 6 months after MMA ! GTA was statistically signif-

icantly lower than the preoperative RDI (P # .01).The increase in oxygen saturation nadir was nearstatistical significance (P # .06).

DiscussionAlthough certain upper airway parameters have

been shown to correlate with the presence and se-verity of OSA,4-10,20 the changes in these parametersafter MMA and correlation with relief of symptoms

Table 3. CT MEASUREMENT OF AIRWAY ANATOMY IN PATIENTS WITH OSA BEFORE AND AFTER MMA

Preoperative Postoperative P Value* Direction

SizeVOL (mL) 12.8 & 5.1 (5.4-19.9) 20.6 & 8.7 (5.6-37.1) .02 1SA 59.0 & 15.8 (30.7-79.9) 74.5 & 13.5 (44.2-92.9) ".01 1Length (mm) 74.8 & 6.5 (66.4-88.2) 70.7 & 7.8 (61.4-84.7) ".01 2Mean CSA (mm2) 168.8 & 57.8 (81.8-243.8) 286.9 & 123.1 (82.2-474.6) .01 1RP (mm) 70.5 & 43 (0-148.7) 206.8 & 127.1 (26.6-452.6) ".01 1RG (mm) 105.8 & 57 (26.0-193.6) 261.2 & 205.5 (32.3-777.6) .04 1Minimum CSA (mm2) 60.5 & 39.3 (0-148.7) 196.2 & 136.6 (26.6-452.6) .01 1LAT (mm) 26.0 & 6.7 (17.3-35.2) 31.6 & 4.5 (23.2-36.7) ".01 1AP (mm) 10.3 & 3.9 (5.2-16.0) 14.6 & 6.0 (5.4-25.2) ".01 1GH (mm) 37.7 & 7.0 (28.7-51.1) 46.0 & 7.4 (32.7-55.4) ".01 1

ShapeLAT/AP 2.7 & 0.7 (1.5-3.8) 2.5 & 0.9 (1.4-4.3) .37 !RP/RG 0.9 & 0.7 (0-2.3) 1.1 & 1.1 (0.3-4.2) .6 !U 0.4 & 0.2 (0-0.7) 0.6 & 0.3 (0.01-1.0) .04 1PSI 0.4 & 0.1 (0.4-0.5) 0.5 & 0.1 (0.2-0.7) .19 !

NOTE. Data are listed as mean & SD (range).*P values computed by use of Wilcoxon signed rank test. P " .05 was considered statistically significant.


Table 4. CT MEASUREMENT OF AIRWAY ANATOMY IN PATIENTS WITHOUT OSA AND THOSE WITH OSA BOTHBEFORE AND AFTER MMA

Non-OSA(n # 17)

Before MMA(n # 11)

P (Non-OSA vsBefore MMA)*

After MMA(n # 11)

P (Non-OSA vsAfter MMA)*

SizeVOL 12.3 & 4.6 12.8 & 5.1 .85 20.6 & 8.7 " .01SA 56.3 & 16.2 59.0 & 15.8 .71 74.5 & 13.5 " .01Length 66.3 & 10.1 74.8 & 6.5 .01 70.7 & 7.8 " .01Mean CSA 181.6 & 55.2 168.8 & 57.8 " .01 286.9 & 123.1 .03RP 80.2 & 52.4 70.5 & 43 .78 206.8 & 127.1 " .01RG 147.0 & 60.1 105.8 & 57 .08 261.2 & 205.5 .08Minimum CSA 73.9 & 39.2 60.5 & 39.3 .4 196.2 & 136.6 .02LAT 22.3 & 7.7 26.0 & 6.7 .19 31.6 & 4.5 " .01AP 10.9 & 4.1 10.3 & 3.9 .82 14.6 & 6.0 .08GH 33.3 & 3.8 37.7 & 7.0 .1 46.0 & 7.4 " .01

ShapeLAT/AP 2.4 & 1.4 2.7 & 0.7 .23 2.5 & 0.9 .46RP/RG 0.6 & 0.4 0.9 & 0.7 .12 1.1 & 1.1 .02U 0.4 & 0.2 0.4 & 0.2 " .01 0.6 & 0.3 .04PSI 0.5 & 0.1 0.4 & 0.1 .71 0.5 & 0.1 .03

NOTE. Data are listed as mean & SD.*P values computed by use of nonparametric methods (Mann-Whitney U test) given the small sample size and lack of

confirmed normality within the data set. P " .05 was considered statistically significant.



have not been well established.11-14 In the sagittalplane, posterior airway space and airway length havebeen shown to improve after MMA and are associatedwith improvement in symptoms.2,15,16,22,26 MMA,however, alters airway anatomy in multiple planes ofspace. Therefore 3D changes in airway parametersmay better predict changes in symptoms, after MMA,than 2D cephalometric measurements. The aims ofthis study were 1) to evaluate 3D changes in airwaysize and shape in patients with OSA after MMA !GTA, 2) to compare preoperative and postoperativeairway measures with adult asymptomatic controlsubjects (not age-matched), and 3) to correlate airwaychanges with changes in subjective reporting ofsymptoms. We hypothesized that the upper airwayafter MMA ! GTA would be shorter in length butlarger in size (volume and CSA) and more uniform andthat it would more closely resemble the airway in thecontrol population. Our findings suggest that, as aresult of MMA ! GTA, the upper airway is enlarged inboth the sagittal and transverse planes and shortenedvertically (Fig 2). These changes all result in de-creased resistance to airflow, as described by Poi-seuille’s equation (Fig 3).

If the upper airway is considered to be a cylinder,resistance to airflow will be inversely proportional tothe fourth power of the airway radius and directlyproportional to airway length based on Poiseuille’slaw. Both sagittal (eg, narrow airways) and vertical(eg, long airways) parameters may increase resistanceto airflow. In addition, the total airway resistance to

flow will be the sum of all obstructions along itslength. Therefore operations that alter multiple com-ponents of upper airway anatomy (eg, MMA ! GTA)should result in larger decreases in resistance to air-flow than those that have a more limited effect (eg,uvulopalatoplasty).

Although many investigators have documented 3Dairway changes with oral appliance therapy,27,28

there are few data regarding 3D airway changes afterMMA surgery.16,17,26,29 Yu et al17 found that the CSAof the narrowest part of the upper airway was in-creased in all dimensions after MMA. Fairburn et al16

examined the effects of MMA on LAT/AP ratio inpatients with OSA and found that both the lateral andanteroposterior dimensions increased after surgeryand the LAT/AP ratio increased at the retroglossallevel. In this study low LAT/AP ratios, correspondingto rounder airways, were also associated with moresevere OSA preoperatively. Although increases inboth the lateral and AP dimensions also occurred afterMMA, the retroglossal LAT/AP ratio did not change, incontrast to the findings of Fairburn et al in 2007. Thisdifference may be the result of the small numbers ofpatients in both studies or the different means bywhich each study selected the retroglossal level.

Airway collapse occurs because of resistance toairflow resulting in a decrease in intra-airway pressurebelow that of the pressure required to maintain pa-tency (critical pressure).30 According to Poiseuille’slaw, resistance is proportional to length and inverselyproportional to the radius to the fourth power. All of

Table 5. SUBJECTIVE CHANGES IN PATIENT-REPORTED SYMPTOMS AFTER MMA " GTA

Patient Preoperative SymptomsPostoperative

Symptoms

Polysomnographic Data

RDI (Events perHour)* SpO2 min (%)†

Preoperative Postoperative Preoperative Postoperative

1 Daytime sleepiness, snoring None 51 7 93 932 Daytime sleepiness, poor sleep None 31 18 85 873 Daytime sleepiness, difficulty concentrating None 16 NA 89 NA4 Daytime sleepiness, snoring, sleeping while

drivingNone 54.8 14 73 87

5 Daytime sleepiness, snoring, headaches None 27 24 91 936 Daytime sleepiness, snoring, sleeping while

driving, poor concentrationNone 111 NA 74 NA

7 Daytime sleepiness, fatigue, poor memory None 38 7 92 908 Daytime sleepiness None 51 NA 87 NA9 Daytime sleepiness None NA NA 60 NA

10 Daytime sleepiness, sleeping while driving,poor concentration

None 48 11 77 90

11 Daytime sleepiness, snoring, fatigue,difficulty breathing

Minimal snoring 28 13 65 NA

Abbreviation: NA, not available.*Preoperative and postoperative RDI compared by use of Wilcoxon signed rank test: P # .01.†Preoperative and postoperative SpO2 min compared by use of Wilcoxon signed rank test: P # .06.


ABRAMSON ET AL 683

the changes in airway anatomy seen in this study arein the direction of decreased airway resistance, that is,larger and shorter airways. Yu et al17 simulated fluiddynamic models and found that a larger upper airwaywith less resistance results in a decreased pressuregradient across the upper airway, effectively loweringcritical pressure.

Polysomnographic studies can be difficult to ob-tain postoperatively because of the relief of symp-toms and lack of patient desire to undergo an addi-tional sleep study. Preoperative and postoperativecomparisons of 3D upper airway anatomy with age-matched asymptomatic control subjects providesupplemental data to assess treatment outcomes inthese patients. The correlation of improvement insymptoms along with normalization of airway sizeis also useful, as is an indirect measure for treat-ment effect. Specifically, if the patient has purelyobstructive sleep apnea, normalization of airwayparameters associated with disease would be ex-pected to result in cure.

In cases in which a central component of diseaseremains because of a hyperactive chemo-reflex (com-

plex sleep apnea), relief of obstruction can exacer-bate the effects of hyperventilation and increase thenumber of apneic events. This is because complexsleep apnea is caused by a hyperactive chemo-reflex,which is triggered by increases in partial pressure ofcarbon dioxide and mediated by hyperventilation,leading to a drop in partial pressure of carbon dioxidebelow the apnea threshold.31 Therefore relief of ob-struction can enhance the effects of hyperventilation,or normal unobstructed ventilation, and trigger theapnea response more frequently.32

On the basis of our referral pattern, our patientbase includes patients with complex sleep apnea inwhom postoperative sleep studies may not improveas much as the clinical symptoms. This may be be-cause of hyperactive chemo-reflex–mediated disease.After MMA ! GTA in patients with complex sleepapnea, respiratory stability and positive sleep archi-tecture may not restore spontaneously within 6months and may require the aid of chemo-modula-tion.31 For this reason, postoperative sleep studiesmay not show improvement and are not used as theprimary outcome measure in this study.

FIGURE 2. Preoperative (blue) and postoperative (purple) retroglossal axial and midsagittal slices of upper airway in patient with OSA. Theincrease in lateral and AP distances, the increase in overall airway size, and the decrease in airway length should be noted. A Shows thecross-section of a pre-operative airway at the level of the retroglossal plane. B Shows a sagittal view of the same pre-operative scan with a3-D reconstructed airway. C and D Show the respective post-operative axial and sagittal views of the airway. Note the increase in size ofthe airway and change in shape demonstrated in C and D relative to preoperative A and B.Abramson et al. CT Airway Analysis and OSA. J Oral Maxillofac Surg 2011.


Though limited by a small sample size, the data inthis study show that there is a global change in thesize and shape of the upper airway as a result of MMA !GTA, in concordance with a decrease in the RDI.Notably, changes in airway volume were stronglycorrelated with the changes in RDI (r # 0.8, P # .03).Given the small sample size and the fact that not allpatients underwent postoperative sleep studies, wewere unable to confirm changes in other airway pa-rameters as predictive of changes in RDI.

Although small sample size is a limitation of thisstudy, statistical significance was achieved, indicatingthat the treatment effect is large enough to be de-tected in a limited sample. However, the small samplesize does limit the ability to generalize the results ofthis study to other populations of OSA patients, inparticular female and pediatric patients. In time, morepatients will be added to this study population toincrease its extrinsic validity. Because control patientshad no symptoms or clinical evidence of breathing- orsleep-related symptoms, they did not have overnightpolysomnograms to confirm the absence of OSA. An-other potential limitation is that the CT scans in thisstudy were done in awake supine patients withoutstandardization of head position. However, the pa-tients served as their own controls and presumablytheir wake status and head position while supinewere similar preoperatively and postoperatively. Al-though CT scans performed on awake patients do notnecessarily reflect the anatomy or physiology of theupper airway during sleep, an abnormal finding onawake CT is likely to be indicative of an abnormal CTfinding during sleep. This is because upper airwaymotor tone is less during sleep, which in theory

should exacerbate any airway constrictions duringwakefulness. This may explain why despite the pit-falls described previously, airway anatomy on supineCT scans can be correlated with the presence andseverity of OSA.

The long-term goal of this project is to evaluate anddocument the efficacy of 3D upper airway analysis forthe purposes of diagnosis, treatment planning, andoutcomes assessment of patients with OSA. The re-sults of this study indicate that in patients with OSA,MMA ! GTA results in airway changes consistentwith a decrease in airway resistance. In this smallgroup of patients, these airway changes were accom-panied by improvements in sleep and breathing asshown by subjective report, polysomnography, andthe ability to sleep without CPAP.

Acknowledgments

The authors acknowledge Dr Thomas Dodson for his input re-garding study design and statistical analysis.

References1. Guilleminault C, Riley R, Powell N: Obstructive sleep apnea

and abnormal cephalometric measurements. Implications fortreatment. Chest 86:793, 1984

2. Riley RW, Powell NB, Li KK, et al: Surgery and obstructivesleep apnea: Long-term outcomes. Otolaryngol Head NeckSurg, Mar 122:415, 2000

3. Partinen M, Guilleminault C, Quera-Salva M, et al: Obstructivesleep apnea and cephalometric roentgenograms. The role ofanatomic upper airway abnormalities in the definition of ab-normal breathing during sleep. Chest 93:1199, 1988

4. Chen NH, Li KK, Li, et al: Airway assessment by volumetriccomputed tomography in snorers and subjects with obstruc-tive sleep apnea in a Far-East Asian population. Laryngoscope112:721, 2002

5. Li H, Chen N, Wang C, et al: Use of 3-dimensional computedtomography scan to evaluate upper airway patency for patientsundergoing sleep disordered breathing surgery 129:336, 2003

6. Lan Z, Itoi A, Takashima M, et al: Difference of pharyngealmorphology and mechanical property between OSAHA pa-tients and normal subjects. Auris Nasus Larynx 33:433, 2006

7. Vos W, De Backer J, Devolder A, et al: Correlation betweenseverity of sleep apnea and upper airway morphology based onadvanced anatomical and functional imaging. J Biomech 40:2207, 2007

8. Verin E, Tardif C, Buffet X, et al: Comparison between anatomyand resistance of upper airway in normal subjects, snorers andOSAS patients. Respir Physiol 129:335, 2002

9. Caballero P, Alvares-Sala R, Garcia-Rio F, et al: CT evaluation ofthe upper airway in healthy subjects and in patients withobstructive sleep apnea syndrome. Chest 113:111, 1998

10. Schwab RJ, Gupta KB, Gefter WB, et al: Upper airway and softtissue anatomy in normal subjects and in patients with sleep-disordered breathing; Significance of lateral pharyngeal walls.Am J Respir Crit Care Med 152:1673, 1995

11. Boyd SB: Management of obstructive sleep apnea by maxillo-mandibular advancement. Oral Maxillofac Surg Clin North Am21:447, 2009

12. Lye KW, Waite PD, Meara D, et al: Quality of life evaluation ofmaxillomandibular advancement surgery for treatment of ob-structive sleep apnea. J Oral Maxillofac Surg 66:968, 2008

13. Prinsell JR: Maxillomandibular advancement surgery in a site-specific treatment approach for obstructive sleep apnea in 50consecutive patients. Chest 116:1519, 1999

FIGURE 3. Rationale for decreased airway resistance after MMA.Shorter and wider airways (postoperatively) offer less resistance toairflow, in accordance with Poiseuille’s law.Abramson et al. CT Airway Analysis and OSA. J Oral MaxillofacSurg 2011.

ABRAMSON ET AL 685

14. Sher AE, Schechtman KB, Piccirillo JF: The efficacy of surgicalmodifications of the upper airway in adults with obstructivesleep apnea syndrome. Sleep 19:156, 1996

15. Li KK, Guilleminault C, Riley RW, et al: Obstructive sleepapnea and maxillomandibular advancement: An assessment ofairway changes using radiographic and nasopharyngoscopicexamination. J Oral Maxillofac Surg 60:526, 2002

16. Fairburn SC, Waite PD, Vilos G, et al: Three-dimensionalchanges in upper airways of patients with obstructive sleepapnea following maxillomandibular advancement. J Oral Max-illofac Surg 65:6, 2007

17. Yu CC, Hsiao HD, Lee LC, et al: Computational fluid dynamicstudy on obstructive sleep apnea syndrome treated with max-illomandibular advancement. J Craniofac Surg 20:426, 2009

18. Abramson Z, Susarla S, Troulis M, et al: Age-related changes ofthe upper airway assessed by 3-dimensional computed tomog-raphy. J Craniofac Surg 20:657, 2009 (suppl 1)

19. Susarla S, Abramson Z, Dodson T, et al: Cephalometric mea-surement of upper airway length correlates with the presenceand severity of obstructive sleep apnea. J Oral Maxillofac Surg68:2846, 2010

20. Abramson Z, Susarla S, August M, et al: Three-dimensional com-puted tomographic analysis of airway anatomy in patients withobstructive sleep apnea. J Oral Maxillofac Surg 68:354, 2010

21. Li KK, Riley RW, Powell NB, et al: Obstructive sleep apneasurgery: Genioglossus advancement revisited. J Oral MaxillofacSurg 59:1181, 2001

22. Abramson Z, Susarla S, Tagoni J, et al: Three-dimensional com-puted tomographic analysis of airway anatomy. J Oral Maxillo-fac Surg 68:363, 2010

23. Kim KD, Ruprecht A, Wang G, et al: Accuracy of facial softtissue thickness measurements in personal computer-based

multiplanar reconstructed computed tomographic images.Forensic Sci Int 155:28, 2005

24. Lye K, Waite P, Wang D, et al: Predictability of prebent ad-vancement plates for use in maxillomandibular advancementsurgery. J Oral Maxillofac Surg 66:1625, 2008

25. Turvey T, Bell B, Phillips C, et al: Self-reinforced biodegradablescrew fixation compared with titanium screw fixation in man-dibular advancement. J Oral Maxillofac Surg 64:40, 2006

26. Eggensperger N, Smolka K, Johner A, et al: Long-term changesof hyoid bone and pharyngeal airway size following advance-ment of the mandible. Oral Surg Oral Med Oral Pathol OralRadiol Endod 99:404, 2005

27. Kyung SH, Park YC, Pae EK: Obstructive sleep apnea patientswith the oral appliance experience pharyngeal size and shapechanges in three dimensions. Angle Orthod 75:15, 2005

28. Smith SD: A three-dimensional airway assessment for the treat-ment of snoring and/or sleep apnea with jaw repositioningintraoral appliances: A case study. Cranio 14:332, 1996

29. Lee CH, Kim JW, Lee HJ, et al: An investigation of upper airwaychanges associated with mandibular advancement device usingsleep videofluoroscopy in patients with obstructive sleep ap-nea. Arch Otolaryngol Head Neck Surg 135:910, 2009

30. Patil SP, Schneider H, Schwartz AR, et al: Adult obstructivesleep apnea: Pathophysiology and diagnosis. Chest 132:325,2007

31. Thomas RJ: Strong chemoreflex modulation of sleep-breathing:Some answers but even more questions. J Clin Sleep Med 212,2009

32. Corcoran S, Mysliwiec V, Niven AS, et al: Development ofcentral sleep apnea after maxillofacial surgery for obstructivesleep apnea. J Clin Sleep Med 5:151, 2009


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