Obstructive sleep apnea (OSA) is a disorder characterized by temporary cessation of breathing (apnea) or shallow breathing (hypopnea). The signs and symptoms are repeated apneic and hypopneic episodes during sleep, excessive daytime sleepiness, night sweats, confusion, headaches and reduced attention span. Recent studies have suggested an association between OSA and certain cardiovascular sequelae, such as hypertension and coronary artery disease.

The primary goal of a surgical approach to severe cases of OSA is to resolve or significantly improve the clinical situation, thus avoiding the use of nasal-continuous positive airway pressure (N-CPAP), which is frequently badly tolerated or refused. Empirical studies have suggested that rates for CPAP use range from 30 to 60%. Surgical techniques involving the soft tissues, such as uvulopalatopharyngoplasty, hyoid suspension, partial glossectomy and lingual suspension have given partial but not long-lasting results.

Therefore orthognathic procedures have gained ground. Initially, mandibular advancement alone and more recently, bimaxillary maxillo-mandibular advancement (MMA) and rotation advancement (RA) procedures have been employed. With MMA, all the soft-tissue structures making up the pharyngeal walls are tightened at once; this stops them from collapsing, or reduces this occurrence, by acting on the suprahyoid and palatal muscles and on the lateral musculature of the pharynx. The result is a significant increase in airway space and the resolution of the syndrome in a high (95%) percentage of cases, as well as improved quality of life. While 2D imaging, orthopantomograms and lateral cephalograms have traditionally served as the radiologic standard for airway assessment in OSA and cephalometric measurements are useful for analysing airway size in the sagital plane, they do not depict the three-dimensional (3D) airway anatomy accurately. The most physiologically relevant information is obtained from axial images, perpendicular to the direction of airflow: the axial plane is not visualized on lateral cephalograms. 3D computed tomography (CT)-studies have been used to characterize the airway anatomy and the morphological changes in patients with OSA. A systematic evaluation of OSA patients compared to non-OSA controls, using normative 3D CT upper airway parameters, has been published recently. The results indicate that the presence of OSA is associated with an increase in airway length. Airways that were more elliptical in shape and mediolaterally oriented had a decreased tendency towards obstruction. Only a small number of 3D CT studies with a limited number of patients are available evaluating the morphological changes of the airway in OSA using patients treated with orthognathic surgery procedures. The authors hypothesize that 3D CT analysis of airway size and shape in patients with OSA will provide reliable and clinically useful information to supplement or finally replace that provided by 2D cephalograms.

The purpose of the present study was to investigate the 3D morphological and pathophysiological airway changes in OSA patients following the bimaxillary rotation advancement procedure.

Materials and methods

This is a retrospective study of 17 patients (10 male and 7 female) with OSA who were treated by the third author (HFS). Patients included in this study had severe clinical OSA symptoms, and the diagnosis was confirmed by overnight polysomnogram findings. 11 patients had previously undergone other surgery, such as uvuloplasties, septoplasties, tonsillectomies and adenotomies ( Table 1 ), at different institutions with no long-lasting effect. All patients had been undergoing treatment with N-CPAP for some time but had not tolerated it well.

Table 1

Demographic and functional polysomnogram data for the patients and rotation advancement of the mandible.

No.	Age (years)	Gender	Height (cm)	Surgical history	Polysomnogram		Rotation advancement (mm)		Adjunctive surgeries
					Pre-AHI/h	Post-AHI/h	Mandible antero-posteriorly	Maxilla counter-clockwise
1	56	M	180	UP, SP, TA	60	6	9.0	3.5	G, RT
2	63	M	170	UP	65	9	12.0	4.5	G, SP
3	45	M	175	SP, T	74	13	13.0	5	RT
4	29	F	190	TA, UP	36	4	11.0	3.5	G, SP
5	51	M	177	UP, TA	40	3	15.0	4	G, SP, RT
6	48	F	156	UP	50	10	10.0	4	SP, RT
7	42	M	164	None	55	9	10.5	3.5	G, RT
8	37	M	170	None	60	4	10.4	3	G, RT
9	40	F	175	None	26	3	10.2	5	SP
10	33	M	178	UP, T	45	9	12.8	4	G, RT
11	35	M	180	TA	30	5	9.7	3.4	G, RT
12	32	F	164	None	33	3	9.1	4.3	G, SP
13	28	M	190	SP	27	7	12.0	5	None
14	25	F	170	UP, T	39	11	10.5	4.4	G, SP
15	30	F	171	None	40	8	10.4	4.1	G, RT
16	32	F	172	UP, TA	70	7	10.6	4	G, SP, RT
17	31	M	174	None	65	10	10.0	3	G, RT
Mean	38.64 ± 10.75		173.9 ± 8.64		47.94 ± 15.64	5.64 ± 2.09	11.84 ± 1.82	4.10 ± 0.60
Min	25		156		26	2	9	3
Max	63		190		74	12	15	5

 

M, male; F, female; UP, uvulopalatopharyngeoplasty; SP, septoplasty; T, tonsillectomy; TA, tonsillectomy and adenoidectomy; G, genioplasty; RT, reduction of the inferior turbinate.

The bimaxillary RA procedure was performed in all patients to create harmonic antefacial physiognomies ( Figs. 1 and 2 ). This technique represents a further modification of the MMA procedure. Following a Le Fort I osteotomy and a long sagittal splitting of the mandible, the maxilla was advanced forward and mainly rotated anti-clockwise to create a new inclination angle of the occlusional and maxillary plane. The mean antero-posterior advancement of the mandible was 11.84 ± 1.82 mm, measured perpendicular to the sagittal plane, and the mean anti-clockwise rotation of the maxilla was 4.13 ± 1.01 mm, creating a gap in the posterior part of the zygomatic buttress ( Table 1 and Fig. 3 ). The anterior advancement of the maxilla was 2.1 ± 0.53 mm measured parallel to the maxillary plane. The maxilla was fixed with two to three plates (2.0) on each side.

(a) The typical facial backward type physiognomies of OSA patients and (b) an antefacial profile.

(a) Preoperative profile of an OSA patient, showing a backward physiognomy and (b) postoperatively, a harmonic antefacial physiognomy could be achieved following RA surgery.

Superimposed volumetric representation of the skeleton and the soft tissue. (a) Preoperative and (b) postoperative view following RA surgery.

Following the new anti-clockwise rotated occlusional plane, the mandible could be positioned farther anteriorly, as opposed to the conventional MMA procedure, where the maxilla would be positioned too far forward (>10 mm), thus decreasing the nasolabial angle too much and resulting in an unnatural appearance.

The mandible was fixed with 2–4 bicortical screws on each side. In 13 patients an associated genioplasty was performed, following the technique described by Trauner and Obwegeser. Additional septoplasty was carried out in 8 patients and a reduction of the inferior turbinates in 11 patients ( Table 1 ). Maxillo-mandibular fixation was not necessary but patients used maxillo-mandibular bands for 3–4 weeks. Approximately 3–4 months after the RA procedure, all patients underwent an overnight polysomnogram study.

Image acquisition and analysis

Helical maxillofacial noncontrast CT scans (Evolution 6, Siemens, Munich, Germany) consisting of 2.5 mm axial tomograms, with reconstructions in the axial, coronal and sagittal planes, were used. The patients were in the supine position and were instructed to remain still, to not swallow, to place the tongue against the incisor teeth and to hold their breath at the end of exhalation. The mandible was positioned centrally and the lips were relaxed. A reference line of 50 mm was used to calibrate the measurements for each image. Postoperative scans were completed 3–6 months following RA.

The scans were imported into the analysing software ZIB-Amira ^® (Zuse Institute Berlin). Digital 3D model reconstructions of the airways were made using a semiautomatic region growing method with a fixed Hounsfield threshold value ( Figs. 3–5 ). The superior upper airway boundary was defined at the level of the ethmoid cells and the inferior boundary 2 cm below the base of the epiglottis, consistent with methods described in previous studies. A reliable coordinate system consisting of the Frankfort horizontal plane or basal skull plane (BSP) and a median plane was set up ( Fig. 4 ). The boundaries of the compartments were defined parallel through the BSP, indicating the nasal cavity (compartment A) intersected inferior with the posterior nasal spine, the nasopharyngeal compartment (B) with the tip of the uvula as its inferior boundary, the oropharyngeal compartment (C) intersected inferior with the tip of the epiglottis and the hypopharyngeal compartment (D) with its inferior border 2 cm below the base of the epiglottis ( Figs. 4 and 5 ).

The screen capture displays the 3D-view of the skull, including a coordinate system (a) consisting of the BSP and median plane. The screen capture on the right (b) illustrates the segmentation of the airway, including the setup of axial planes systematically parallel to the BSP.

(a) Pre- and (b) postoperative screen capture displaying the sagittal view. The whole airway including the anatomical compartments (nasal cavity, nasopharynx, oropharynx and hypopharynx) was segmented and visualized. The lengths of the airway including all compartments, including the position of the hyoid bone, were measured according to the BSP. The screen capture (b) following rotation advancement surgery clearly illustrates the shortening of the airway and the change in shape, including the cranial positioning of the hyoid bone.

Airway parameters

Once the 3D digital models were constructed, the airway was systematically analysed using metric, 2D and 3D parameters. The following airway parameters ( Tables 2 and 3 ) were used to analyse the anatomical compartments of the airway: volume (VOL), surface area (SA), length (L), CSA, antero-posterior dimension (AP), and medio-lateral dimension (LAT). The LAT/AP ratio and sphericity describes the 3D shape of the airway. The metric and morphological changes of the position of the hyoidal bone following RA surgery were described, measuring the distance of the hyoidal bone to the BSP (L hyo), as well as the distance between the hyoidal bone and the mandible (L mh) and the angle between the hyoid and the mandible ( Figs. 5 and 6 ). All parameters were measured in a reproducible way according to the BSP ( Fig. 4 ). To determine inter-observer variability, a second operator performed the analysis in 7 randomly selected patients in the study group, independent of the first operator.

Table 2

Definition of anatomical compartments and airway parameters.

Airway compartments	Symbol	Definition
Nasal cavity	A	From ethmoid cells to posterior nasal spine
Nasopharynx	B	From posterior nasal spine to tip of the uvula
Oropharynx	C	From tip of uvula to tip of epiglottis
Hypopharynx	D	From tip of epiglottis to 2 cm below the base of the epiglottis

 

Airway parameter	Symbol	Type	Unit	Definition
Length and size of the airway
Airway space
Total	VOL	3D	ml	Airway space
Nasal cavity	VOL A
Nasopharynx	VOL B
Oropharynx	VOL C
Hypopharynx	VOL D
Surface area	SA		cm 2	Surface area of airway
Total	SA tot	2D
Nasal cavity	SA A
Nasopharynx	SA B
Oropharynx	SA C
Hypopharynx	SA D
Length	L	1D	mm	Length of the airway, measured perpendicular to the basal skull plane (BSP)
Total	L tot
Nasal cavity	L A
Nasopharynx	L B
Oropharynx	L C
Hypopharynx	L D
Cross-sectional area	CSA	2D	mm 2	Cross sectional area of the airway, measured parallel to the basal skull plane
Nasopharynx	CSA B
Oropharynx	CSA C
Hypopharynx	CSA D
Minimum	min CSA
Maximum	max CSA
Average	avg CSA
Medio-lateral distance	LAT	1D	mm	Medio-lateral distance of the cross sections of the airways, measured in the axial planes parallel to the basal skull plane
Minimum	LAT B
Maximum	LAT C
Average	avg LAT
Antero-posterior dimension	AP	1D	mm	Antero-posterior distance of the cross sections of the airways, measured in the axial planes parallel to the basal skull plane
Nasopharynx	AP B
Oropharynx	AP C
Hypopharynx	AP D
Minimum	AP min
Maximum	AP max
Average	avg AP
Shape of the airway
LAT/AP ratio	LAT/AP	Ratio	–	Ratios of the medio-lateral and antero-posterior distances, indicating the geometrical shape of the cross-sectional area of the airway in 2D
Nasopharynx	LAT/AP B
Oropharynx	LAT/AP C
Hypopharynx	LAT/AP D
Minimum	LAT/AP min
Maximum	LAT/AP max
Average	LAT/AP avg
Sphericity ( Ψ )/compactness	Ψ	Formula	–	Mathematical measure of the sphericity ( Ψ ) or compactness
Total	Ψ tot			( Ψ ) = [ π 1/3(6 × VOL) 2/3 ]/SA
Nasopharynx	Ψ A			Indicating the 3D shape of the airway, a flat and less compact object has a Ψ of 0 and a sphere and compact object a Ψ of 1
Oropharynx	Ψ B
Hypopharynx	Ψ C
Position of the hyoid bone
Distance of the mandible to hyoid bone	L mh	1D	mm	Distance of the genial tubercle of the mandible to the hyoid bone
Mandible–hyoid angle	α			Angle between the genial tubercle of the mandible and the hyoid bone
Length of the hyoid to the skull base	L hyo			Length of the hyoid bone to basal skull plane

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