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Effects of orthognathic surgery on pharyngeal airway and respiratory function during sleep in patients with mandibular prognathism
Int. J. Oral Maxillofac. Surg. 2014; 43: 1082–1090 http://dx.doi.org/10.1016/j.ijom.2014.06.010, available online at http://www.sciencedirect.com
Clinical Paper Orthognathic Surgery
Effects of orthognathic surgery on pharyngeal airway and respiratory function during sleep in patients with mandibular prognathism
T. Uesugia,*, T. Kobayashia, D. Hasebea, R. Tanakab, M. Ikeb, C. Saitoa a
Division of Reconstructive Surgery for Oral and Maxillofacial Region, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan; b Division of Oral and Maxillofacial Radiology, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
T. Uesugi, T. Kobayashi, D. Hasebe, R. Tanaka, M. Ike, C. Saito: Effects of orthognathic surgery on pharyngeal airway and respiratory function during sleep in patients with mandibular prognathism. Int. J. Oral Maxillofac. Surg. 2014; 43: 1082– 1090. # 2014 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The aim of this study was to determine changes in overnight respiratory function and craniofacial and pharyngeal airway morphology following orthognathic surgery. The subjects were 40 patients in whom mandibular prognathism was corrected by orthognathic surgery: a one-jaw operation in 22 patients and a two-jaw operation in 18 patients. Morphological changes were studied using cone beam computed tomography immediately before surgery and at more than 6 months after surgery, and the apnoea–hypopnoea index (AHI) was measured with a portable polysomnography system. Pharyngeal airway volume was decreased significantly after surgery, especially in the one-jaw operation group. AHI was not changed significantly after surgery in either group, although AHI in one patient in the one-jaw operation group was increased to 19 events/h. There was no significant change in pharyngeal airway morphology in that patient, but he was obesity class 1 and was 54 years old. In conclusion, some patients who are obese, have a large amount of mandibular setback, and/or are of relatively advanced age may develop sleep-disordered breathing after mandibular setback; a two-jaw operation should therefore be considered in skeletal class III patients who have such risks because it decreases the amount of pharyngeal airway space reduction caused by mandibular setback surgery.
Mandibular setback surgery for mandibular prognathism can reduce the space in the pharyngeal airway,1–14 and it has been suggested that it might induce sleep-disor0901-5027/0901082 + 09
dered breathing, typified by obstructive sleep apnoea syndrome (OSAS).4–6,12 We have previously reported cases in whom reduction of the pharyngeal airway space
Key words: mandibular setback surgery; jaw deformity; cone beam computed tomography; pharyngeal airway; respiratory function during sleep. Accepted for publication 23 June 2014 Available online 12 July 2014
and OSAS were caused by mandibular setback surgery.5 OSAS is a potentially life-threatening disorder caused by repetitive narrowing and obstruction of the pha-
# 2014 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Airway changes after orthognathic surgery ryngeal airway during sleep, and it has been associated with loud snoring and apnoea. OSAS is regarded as one of the risk factors of hypertension, ischaemic myocardial diseases, and cerebral vascular diseases.15 It is also thought to be one of the causes of traffic accidents. Lateral cephalograms have been used widely to evaluate craniofacial and pharyngeal airway morphology,1,2,4–9,12– 14,16–18 and lateral cephalometric measurements are useful for analyzing airway size on the sagittal plane; however, they do not accurately reflect the three-dimensional (3D) airway anatomy. Therefore, 3D imaging has been preferred in recent years for evaluating changes of the pharyngeal after orthognathic surairway gery.3,7,10,11,19–25 Conventional spiral computed tomography (CT) and magnetic resonance imaging (MRI) have been the methods of choice for obtaining 3D information on craniofacial and pharyngeal morphology,3,7,11,19,24–26 but their use is limited because of the costs and/or the greater radiation exposure. Cone beam computed tomography (CBCT) is a recently introduced technology that has been used for 3D analyses of craniofacial and pharyngeal morphology because the radiation exposure and the cost are decreased compared with those of conventional CT.10,20–23,27 We are interested in the effects of orthognathic surgery on the pharyngeal airway and respiratory function during sleep in patients with mandibular prognathism. The aim of this study was to determine whether orthognathic surgery causes OSAS with morphological changes after orthognathic surgery in patients with mandibular prognathism. In this study we investigated changes in overnight respiratory function with a portable polysomnography (PSG) system and examined 3D morphological changes in the maxillomandibular skeleton and pharyngeal airway using CBCT before and after orthognathic surgery.
A), and a combination of Le Fort I osteotomy and bilateral sagittal split osteotomy was performed in 18 patients who had mandibular prognathism combined with maxillary retrusion, asymmetry, and/or open bite (group B). None of the subjects had symptoms of OSAS such as snoring or apnoea, and no cases of cleft palate or craniofacial syndrome were included. The mean age of the subjects at surgery was 23 years (range 16–54 years). All of the subjects received pre- and postoperative orthodontic treatment, and osteosynthesis was achieved using a titanium miniplate and resorbable fixation devices. Maxillomandibular fixation was performed 1 day after surgery and was maintained for 14 days. As a control group, 16 subjects (nine males and seven females) with normal occlusion and no symptoms of sleep-disordered breathing underwent the same CBCT examinations as those performed in the patients. The mean age of the control subjects was 26 years (range 21–38 years). The study protocol was approved by the institutional ethics committee and informed consent was obtained from all subjects. Imaging procedure
All of the patients underwent CBCT examinations (CB MercuRay; Hitachi Medical Corporation, Tokyo, Japan) for assessment of craniofacial and pharyngeal morphology before surgery (T0) and at more than 6 months after surgery (mean 9 2.1 months, range 6–12 months) (T1). For the control group, two CBCT images were taken repeatedly on separate days to assess the accuracy of CBCT analyses. The subjects sat upright with the Frankfort horizontal plane parallel to the floor and with centric occlusion. CBCT data of
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the maxillofacial regions were acquired with a 0.38-mm voxel size and 512 512 matrices, using 120 kVp, 15 mA, 9.6-s scan time, and 12-inch detector field. The CBCT data were converted into DICOM (digital imaging and communication in medicine) format, and 3D images of the craniofacial and pharyngeal airway morphology were reconstructed with a 3D image analysis system (INTAGE Realia Pro; Cybernet Systems Co., Ltd, Tokyo, Japan). Since small deviations in the position of the head from ideal are bound to occur, reconstructed 3D images taken before surgery were corrected and re-aligned using the Frankfort horizontal (FH) plane (XY plane), coronal plane (XZ plane), and midsagittal plane (YZ plane) as references. The FH plane was defined by the bilateral uppermost point on the bony external auditory meatus (porion) and lowest point on the right inferior borders of the bony orbit (orbitale). The coronal plane was defined as a plane passing through bilateral porions and perpendicular to the FH plane. The midsagittal plane was defined as a vertical plane passing through the most anterior point of the frontonasal suture (nasion) and perpendicular to the FH plane and coronal plane (Fig. 1). Next, the coordinates of the 3D images obtained at more than 6 months after surgery were adjusted and conformed to the coordinates of the preoperative standardized images by superposition of four anatomical landmarks: nasion (N), posterior clinoid process (PCP), and bilateral most inferior points of the mastoid process (MsR, MsL) (Fig. 2). Measurements of skeletal changes
Unified 3D images were exported in DICOM format and imported into OsiriX (ver. 3.5.1; Pixmeo, Geneva, Switzerland)
Materials and methods
This prospective study included 40 patients (21 males and 19 females) in whom mandibular prognathism was corrected surgically during the period June 2010 to March 2012; agreement to participate in this study was obtained before surgery. There were no drop-outs. The patients were divided into two groups according to the type of orthognathic surgery done. Bilateral sagittal split osteotomies were performed in 22 patients with simple mandibular prognathism (group
Figure 1. Configurations of the three reference planes. Axial (XY) plane: Frankfort horizontal (FH) plane passing through the bilateral uppermost points on the bony external auditory meatus (porion) and lowest point on the right inferior borders of the bony orbit (orbitale). Coronal (XZ) plane: plane passing through bilateral porions and perpendicular to the FH plane. Midsagittal (YZ) plane: vertical plane passing through the most anterior point of the frontonasal suture (nasion) and perpendicular to the FH plane and coronal plane.
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Uesugi et al. part of the epiglottis. The pharyngeal airway was divided into two regions: the nasopharynx (between the upper border of the nasopharynx and PNS planes) and the oropharynx (between the PNS and lower part of the epiglottis planes) (Fig. 4). The two airway volumes were calculated from the voxel numbers of preand postoperative 3D images, and the average of the cross-sectional areas (ACSA) was calculated to exclude the influence of length of the pharyngeal airway. To evaluate the anatomical characteristics of the oropharyngeal airway, the largest transverse width (LTW), anteroposterior length (APL), and cross-sectional area (CSA) of the four axial sections (nasal, palatal, oropharyngeal, and tongue sections) were calculated from the preand postoperative 3D images (Figs. 4–7). Accuracy of CBCT analyses
this line. The pogonion was defined as the most anterior point on the osseous contour of the chin corresponding to this vertical line (Fig. 3).
All measurements were performed by a single examiner to reduce measurement errors. In order to determine the accuracy of CBCT analyses, differences in coordinate values of ANS, PNS, and pogonion between the two CBCT images taken repeatedly in the control group were examined three times and the averages of maximum differences were calculated. Differences in pharyngeal airway measurements between the two CBCT images were also calculated.
Measurements of pharyngeal airway morphology
Measurement of the apnoea–hypopnoea index (AHI)
Pharyngeal airway morphology was analyzed from the unified DICOM data by means of two 3D imaging software programs: INTAGE Realia Pro and ImageJ (ver.1.47a; National Institutes of Health, Bethesda, MD, USA). The pharyngeal airway was defined as the region between horizontal planes passing through the upper border of the nasopharynx and lower
Overnight polysomnography (PSG) using a portable PSG system (PulSleep LS-120; Fukuda Denshi Co., Ltd, Tokyo, Japan) was performed at T0 and T1. The AHI was calculated as the sum of apnoea and hypopnoea events per hour of sleep. An apnoea event was defined as the cessation of airflow for more than 10 s, and a hypopnoea event was defined as 70% of a
Figure 2. Reference points for superposition of anatomical landmarks. (A) Axial (XY) view. (B) Midsagittal (YZ) view. (C) Midsagittal (YZ) view. (D) Coronal (XZ) view. PCP: posterior clinoid process identified on axial (XY) and midsagittal (YZ) views. MsR, MsL: bilateral most inferior points of the mastoid process identified on coronal (XZ) and midsagittal (YZ) views.
to assess movement of the maxilla and mandible. Changes in coordinate values of the ANS, posterior nasal spine (PNS), and pogonion were calculated from the 3D images at T0 and T1. Positive values were assigned to anterior, inferior, and rightward movements. In this procedure, it is difficult to define the pogonion in an asymmetric case because the most anterior point on the osseous contour of the chin is changed after surgery. The pogonion was therefore determined as follows: first, a line was drawn parallel to the y-axis passing through the most anterior point on the osseous contour of the chin corresponding to mental spines in the XY plane, and then a vertical line to yaxis was drawn on the YZ plane matching
Figure 3. Reference points for analyses of skeletal changes. (A) Axial (XY) view of the maxilla. (B) Axial (XY) view of the mandible. (C) Midsagittal (YZ) view. ANS: anterior nasal spine identified on axial (XY) and midsagittal (YZ) views. PNS: posterior nasal spine identified on axial (XY) and midsagittal (YZ) views. Pogonion: most anterior point on the osseous contour of the chin identified on axial (XY) and midsagittal (YZ) views.
Airway changes after orthognathic surgery
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Figure 4. Measurement of pharyngeal airway morphology. (A) Lateral airway image obtained using a volume rendering technique. The pharyngeal airway was defined as the region between horizontal planes passing through the upper border of the nasopharynx and lower part of the epiglottis. The black rectangle indicates the measurement range. (B) Lateral view of the extracted airway. (C) Frontal view of the extracted airway. Dotted lines indicate the four axial sections for pharyngeal airway measurements: N, nasal section; P, palatal section; O, oropharyngeal section; T, tongue section.
normal breath and/or a 4% drop in SpO2 during sleep. Statistical analysis
Mean values and standard deviations were calculated for all measured parameters. Since it could not be assumed that the parameters had normal distributions, Friedman’s test was used to determine whether changes in each parameter had significance in their groups. After the significance of the parameters was proved, Wilcoxon’s matched-pair signed rank sum test was used to assess the significance of differences in paired parameters in each
group. Spearman’s correlation analysis was performed to assess the correlation between each parameter. Probabilities of less than 0.05 were accepted as significant. Data were analyzed using IBM SPSS Statistics 20 for Windows (IBM Corp., Armonk, NY, USA). Results
The mean body mass index (BMI) values of the patients at T0 and T1 were 21.1 kg/ m2 (range 15–34.4 kg/m2) and 20.9 kg/m2 (range 15.2–33.8 kg/m2), respectively. The mean BMI values in the control group at the first and second measurements were
22.1 kg/m2 (range 17.8–26.4 kg/m2) and 22.1 kg/m2 (range 17.8–26.1 kg/m2), respectively. There were no significant differences between the mean BMI values. Accuracy of CBCT analyses
The differences in coordinate values of ANS, PNS, and pogonion between the two CBCT images of the control group were in the range 0.24–0.48 mm on average, which seemed to be acceptable accuracy (Table 1). For the pharyngeal airway measurements, the differences in volumes were 0.4 to 0.1 cm3, the difference in ACSA was 0 cm2, the differences in CSA 0.07 to on four axial planes were 0.13 cm2, and the differences in LTW and APL on four axial planes were 0.8 to 0.8 mm (Table 2). Skeletal changes following orthognathic surgery
The maxilla moved in an anterosuperior direction and rotated clockwise on average in group B, and the mandible moved posterosuperiorly at pogonion on average in both groups. There was no significant difference in the amounts of mandibular movement between the two groups, although the amount of movement in group A was greater than that in group B (Table 3). Pharyngeal airway changes following orthognathic surgery
Figure 5. Four axial sections for pharyngeal airway measurements. (A) Nasal section: plane passing through the Eustachian orifice (Eo) and parallel to the FH plane. (B) Palatal section: plane passing through the PNS and parallel to the FH plane. (C) Oropharyngeal section: plane passing through the most prominent point of the palatine tonsil to the pharyngeal airway (Pt) and parallel to the FH plane. (D) Tongue section: plane passing through the most posterior point of the lingual radix (Plr) and parallel to the FH plane.
Oropharyngeal airway volume, LTW on four axial planes, and APL and CSA on two axial planes of the oropharyngeal area, were significantly decreased in group A at more than 6 months after surgery
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Uesugi et al. the pogonion was significantly correlated with reductions in the volume of the pharynx and LTW, APL, and CSA in the palatal section in group A (Table 7). In group B, the amount of superior movement at the pogonion was significantly correlated with a reduction in only CSA in the palatal section (Table 8). There was no correlation between AHI and BMI, age, or pharyngeal airway changes in either group. Discussion
Figure 6. Cross-sectional area (CSA) measurements of the pharyngeal airway. (A) Ordinal axial bone image. (B) Binarized image from which the air density area of the pharyngeal space was extracted and measured on four axial sections.
Figure 7. Linear measurements of the pharyngeal airway. (A) Anteroposterior length (APL) of the pharyngeal airway. (B) Largest transverse width (LTW) of the pharyngeal airway. APL and LTW were each measured on four axial sections.
(Table 4). In contrast, only APL of the nasal section was significantly increased in group B at more than 6 months after surgery (Table 5). Table 1. Differences in coordinate values between the two CBCT images in the control group (n = 16). Differences in coordinate values, mm ANS x-Axis y-Axis z-Axis PNS x-Axis y-Axis z-Axis Pogonion x-Axis y-Axis z-Axis
0.46 0.4 0.31 0.41 0.24 0.26 0.48 0.39 0.42
CBCT, cone beam computed tomography; ANS, anterior nasal spine; PNS, posterior nasal spine.
Measurements of AHI
There was no significant difference between AHI values before and at more than 6 months after surgery in either group, and there was no significant difference between the two groups at any stage (Table 6). One patient was diagnosed with moderate OSAS after surgery because AHI increased to 19 events/h from the preoperative 14.9 events/ h. He was a 54-year-old male with obesity class 1 (BMI of 34.4 kg/m2 before surgery and 33.8 kg/m2 more than 6 months after surgery) who underwent one-jaw surgery. He did not have subjective symptoms of OSAS before or at more than 6 months after surgery, but showed a large amount of mandibular setback at surgery (10.1 mm backward at pogonion), although there was no significant change in the pharyngeal airway.
Correlations
Spearman’s correlation analysis showed that the amount of superior movement at
Several reports have suggested that mandibular setback surgery might induce disordered breathing.4–6,9,12 Sleepdisordered breathing typified by OSAS has been identified as a major cause of sleep disturbance and is typically recognized by symptoms such as extreme daysleepiness, severe snoring, time obstruction of the pharyngeal airway, and hypoxaemia during sleep. Obstruction that causes episodes of apnoea is the result of collapse of the pharyngeal airway and usually occurs at the oropharynx or velopharynx. Genetic and environmental factors for the development of obstructive sleep apnoea have been linked to obesity, skeletal conditions such as a short mandibular body and mandibular retreat, large tongue or uvula, shape of the airway, age, and ethnicity.16,28 To prevent the development of obstructive sleep apnoea after mandibular setback, it is important to evaluate the risk and to design a plan for orthognathic surgery, which is what we have done. In this study, the effects of mandibular setback surgery on craniofacial and pharyngeal morphology and on respiratory function during sleep were investigated. Since the airway is a 3D space surrounded by soft tissues, 3D image analysis is necessary for accurate assessment. The recently introduced CBCT examination has the advantages of a lower radiation dose and lower cost than those of other CT systems such as spiral CT. Therefore, we used CBCT to quantify the 3D changes in skeletal and pharyngeal airway morphology after orthognathic surgery. The volumes of the nasopharyngeal and oropharyngeal regions, ACSA, and APL, LTW, and CSA on four axial planes, were calculated in the present study as an alternative approach to the analysis of anatomical characteristics of the pharyngeal airway. Our CBCT analysis method appears to have acceptable accuracy, although the standard deviations of the differences in CSA on each axial plane were greater than those of the other parameters.
Airway changes after orthognathic surgery Table 2. Differences in pharyngeal airway measurements between the two CBCT images in the control group (n = 16).a Volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) ACSA (cm2) Nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
First
Second
Difference
8 4.2 15.4 7.9 23.4 11.9 2.83 1.25
7.9 3.7 15.8 8.7 23.7 12.1 2.87 1.27
0.1 0.8 0.4 2.7 0.3 3 00
4.53 1.39 19.4 4.2 22.8 3.3
4.53 1.32 19.1 4.1 23 2.3
0 0.3 0.3 1.2 0.2 1.7
5.54 2.33 20.5 3.8 20.9 3.6
5.48 2.29 20.7 3.7 20.8 3.7
0.06 0.77 0.2 1.3 0 1.3
2.59 1.75 10.5 4.3 18.3 6.8
2.67 1.8 10.7 3.9 19.1 6.7
0.07 0.51 0.2 1.6 0.8 3.1
2.93 1.29 11.1 2.8 29.8 5.7
2.8 1.39 10.3 3 30.3 4.8
0.13 0.52 0.8 1.7 0.6 2.7
CBCT, cone beam computed tomography; ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Values are given as the mean standard deviation.
It appears that the cross-sectional surfaces on four axial planes of the pharyngeal airway are affected by a slight inclination of the head, because the pharyngeal airway is composed of soft tissues with complex configurations such as the soft palate, tongue base, and pharyngeal recess. On the other hand, it appears that linear measurements are almost unchanged on the same axial planes because indicators of linear measurement such as the deepest point of the pharyngeal wall do not change significantly with a slight inclination of the head. Recently, several techniques to assess 3D skeletal and pharyngeal airway Table 3. Positional changes in skeletal reference points following orthognathic surgery.a Group A (n = 22) ANS x-axis y-axis z-axis PNS x-axis y-axis z-axis Pogonion x-axis y-axis z-axis
Group B (n = 18)
– – –
0.2 0.9 0.6 1.2 0.3 0.9
– – –
0.3 0.5 2.1 0.9 1.0 1.5
1.6 2.6 4.9 2.2 1.0 1.4
1.1 4.6 3.2 3.2 1.8 2.4
ANS, anterior nasal spine; PNS, posterior nasal spine. a Values are given as the mean standard deviation, in mm.
changes after orthognathic surgery with images have been CT reported.3,7,10,11,23,27 Some authors3,7,23 have reported the pharyngeal airway space to be reduced mainly in the oropharynx region after mandibular setback surgery. Similarly, oropharynx volume, total pharynx volume, ACSA, N-LTW, P-LTW, OCSA, O-APL, O-LTW, T-CSA, T-APL,
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and T-LTW in the one-jaw surgery group were significantly decreased in the present study, though only N-APL was significantly increased in group B. On the other hand, Park et al.23 reported that there was no significant reduction in the pharyngeal airway space after mandibular setback surgery and suggested that the pharyngeal airway might transform to preserve pharyngeal airway capacity in the changed environment after mandibular setback surgery. In the present study, superior mandibular movements at the pogonion showed correlations to reductions in the pharyngeal airway mainly in the palatal section in both groups. Even though the amount of superior movements at the pogonion in group B was greater than that in group A, pharyngeal airway volume was not decreased significantly in group B. One possible reason for this is that maxillary advancement was combined with mandibular setback in group B. Several studies have shown that bimaxillary surgery diminishes the amount of pharyngeal airway reduction caused by mandibular setback surgery.2,4,9,10,23 Lee et al.10 reported that a greater clockwise rotation of the maxilla and mandible as a complex and a greater increase in the upper part (between the upper border of the nasopharynx and first cervical vertebra planes) and decrease in the lower part (between the first cervical vertebra planes and third cervical vertebra planes) of the airway,
Table 4. Results of pharyngeal airway measurements for group A (n = 22).a Volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) ACSA (cm2) Nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
T0
T1
8.6 3.4 16.5 7.5** 25.1 10.6** 3.12 1.15**
7.8 2.6 12.5 4.7** 20.3 6.8** 2.36 0.76**
3.98 0.9 18.1 3.3 23.5 2.7**
4.02 1.06 17.7 3.9 22.9 2.6**
5.21 1.71 20.3 4.1 23.8 5.3**
4.92 1.62 19.8 4.4 22.6 5.4**
3.31 1.78** 13.4 4** 19.8 6.6**
2.27 1.07** 11.3 3.3** 17.6 6.5**
2.99 1.22** 11.6 2.8* 29.8 5.5*
2.29 0.79** 10.0 2.1* 28.6 5.6*
ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Values are given as the mean standard deviation. Statistically significant difference between T0 and T1: **P < 0.01, *P < 0.05.
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Table 5. Results of pharyngeal airway measurements for group B (n = 18).a Volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) ACSA (cm2) Nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
T0
T1
6.7 2.7 14.8 5.7 21.5 7.9 2.74 0.83
7.2 2.6 14.2 6 21.3 8 2.7 0.8
3.3 0.83 16.2 3.9* 22.9 1.7
3.55 0.72 17.1 3.5* 22.7 2.1
4.19 1.66 17.4 4.9 21.5 5.5
4.49 1.3 18.9 3.4 22.6 4.9
3.02 1.48 12.6 3.9 19.5 6.9
2.79 1.23 12.2 4 18.9 7.4
2.79 1 10.9 3.4 30.5 4
2.7 0.9 10.6 3.1 30.5 3.5
ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Values are given as the mean standard deviation. Statistically significant difference between T0 and T1: *P < 0.05.
were found after bimaxillary surgery, and total airway volume was therefore not changed. In the present study, there was little increase in nasopharynx volumes because of the small amounts of anterior and superior movements of the maxilla. Full overnight PSG is important for the diagnosis of sleep-disordered breathing. However, the use of full PSG is limited because of economic and manpower problems. We used a portable PSG system, which is classified as a type III sleep monitor by the US Centers for Medicare and Medicaid Services (CMS) and the American Academy of Sleep Medicine (AASM) guidelines, for patients treated with orthognathic surgery. A portable PSG system could be useful for prompt diagnosis if we know the characteristics and weak points caused by decreased PSG parameters, especially lack of electroencephalography (EEG).29,30 Hochban et al.6 reported that there was no evidence of postoperative sleep-disordered breathing in 16 patients who underwent Table 6. Apnoea–hypopnoea index (AHI, number/h) measured with a portable polysomnography system.a Group A (n = 22) Group B (n = 18) a
T0
T1
3.1 3.2 1.9 1.7
3.4 4.1 2.2 2.1
Values are given as the mean standard deviation.
mandibular setback surgery, even though the pharyngeal airway was decreased after surgery. In a previous study by our group,5 in which 22 patients with mandibular prognathism were examined by full PSG before and 6 months after mandibular setback surgery (average 7.1 mm backward at
pogonion), AHI was not changed significantly after surgery, although two patients who underwent a large amount of mandibular setback (12.6 mm and 13.7 mm backward at pogonion) were diagnosed with mild OSAS after surgery. Similarly, in the present study using a portable PSG system, there were no significant changes in AHI and no signs of sleep-disordered breathing after surgery, although AHI in one patient was increased to 19 events/h after surgery (preoperative AHI: 14.9 events/h). In that patient, there was no significant change in pharyngeal airway, but he was obesity class 1 and was 54 years old, and he had a comparatively large amount of mandibular setback (10.1 mm backward at pogonion). In this patient, the amount of mandibular setback should have been decreased by maxillary advancement, but the patient did not accept two-jaw surgery. Several reports9,21,28 have shown ageing, obesity, and a large amount of mandibular setback to be risk factors for OSAS. In a previous study by our group,9 positive correlations between BMI and oximetry indices were found in 78 patients who underwent mandibular setback surgery. Therefore, it appears that patients who are obese, who have a large amount of mandibular setback, and/or who are of advanced age are at risk for the development of OSAS after mandibular setback surgery. Preoperative weight loss should be recommended to obese patients because orthognathic surgery is elective surgery.
Table 7. Spearman’s rank correlation coefficient between mandibular movements at pogonion and reductions in pharyngeal airway measurements for group A (n = 22).a
Reductions in volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) Reductions in ACSA (cm2) Reductions in nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Reductions in palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Reductions in oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Reductions in tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
Posterior movements at pogonion
Superior movements at pogonion
0.089 0.108 0.104 0.084
0.428* 0.494* 0.357 0.416
0.127 0.153 0.359
0.063 0.016 0.063
0.264 0.05 0.097
0.434* 0.616** 0.45*
0.224 0.165 0.387
0.391 0.454* 0.234
0.247 0.311 0.376
0.276 0.248 0.066
ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Significant difference: **P < 0.01, *P < 0.05.
Airway changes after orthognathic surgery Table 8. Spearman’s rank correlation coefficient between mandibular movements at pogonion and reductions in pharyngeal airway measurements for group B (n = 18).a
Reductions of volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) Reductions of ACSA (cm2) Reductions of nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Reductions of palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Reductions of oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Reductions of tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
Posterior movements at pogonion
Superior movements at pogonion
0.179 0.022 0.263 0.191
0.379 0.35 0.275 0.381
0.23 0.275 0.243
0.21 0.025 0.175
0.166 0.199 0.014
0.583* 0.273 0.353
0.292 0.12 0.11
0.323 0.367 0.29
0.125 0.049 0.044
0.073 0.251 0.07
ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Significant difference: *P < 0.05.
In conclusion, there was no evidence of sleep-disordered breathing after mandibular setback surgery. However, patients with certain risk factors such as obesity, a large amount of mandibular setback, and/or advanced age may develop sleepdisordered breathing after mandibular setback surgery. In such patients, it might be better to consider a combination of Le Fort I osteotomy and bilateral sagittal split osteotomy to reduce the narrowing of the pharyngeal airway, and careful attention should be paid to respiratory function during sleep after surgery. Funding
None. Competing interests
None declared. Ethical approval
This study was reviewed and approved by the Ethics Committee of Niigata University. References 1. Becker OE, Avelar RL, Go¨elzer JG, Dolzan Ado N, Haas Jr OL, De Oliveira RB. Pharyngeal airway changes in class III patients treated with double jaw orthognathic surgery—maxillary advancement and mandibular setback. J Oral Maxillofac Surg 2012;70:639–47.
2. Chen F, Terada K, Hua Y, Saito I. Effects of bimaxillary surgery and mandibular setback surgery on pharyngeal airway measurements in patients with Class III skeletal deformities. Am J Orthod Dentofacial Orthop 2007;131:372–7. 3. Degerliyurt K, Ueki K, Hashiba Y, Marukawa K, Nakagawa K, Yamamoto E. A comparative CT evaluation of pharyngeal airway changes in class III patients receiving bimaxillary surgery or mandibular setback surgery. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;105:495–502. 4. Demetriades N, Chang DJ, Laskarides C, Papageorge M. Effects of mandibular retropositioning, with or without maxillary advancement, on the oro-naso-pharyngeal airway and development of sleep-related breathing disorders. J Oral Maxillofac Surg 2010;68:2431–6. 5. Hasebe D, Kobayashi T, Hasegawa M, Iwamoto T, Kato K, Izumi N, et al. Changes in oropharyngeal airway and respiratory function during sleep after orthognathic surgery in patients with mandibular prognathism. Int J Oral Maxillofac Surg 2011;40:584–92. 6. Hochban W, Schurmann R, Brandenburg U, Conradt R. Mandibular setback for surgical correction of mandibular hyperplasia— does it provoke sleep related breathing disorders. Int J Oral Maxillofac Surg 1996;25: 333–8. 7. Kawamata A, Fujishita M, Ariji Y, Ariji E. Three-dimensional computed tomographic evaluation of morphologic airway changes after mandibular setback osteotomy for prognathism. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:278–87.
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8. Kitahara T, Hoshino Y, Maruyama K, In E, Takahashi I. Changes in the pharyngeal airway space and hyoid bone position after mandibular setback surgery for skeletal Class III jaw deformity in Japanese women. Am J Orthod Dentofacial Orthop 2010;138. 708.e1–10. 9. Kobayashi T, Funayama A, Hasebe D, Kato Y, Yoshizawa M, Saito C. Changes in overnight arterial oxygen saturation after mandibular setback. Br J Oral Maxillofac Surg 2013;51:312–8. 10. Lee Y, Chun YS, Kang N, Kim M. Volumetric changes in the upper airway after bimaxillary surgery for skeletal class III malocclusions: a case series study using 3-dimensional cone-beam computed tomography. J Oral Maxillofac Surg 2012;70: 2867–75. 11. Park JW, Kim NK, Kim JW, Kim MJ, Chang YI. Volumetric, planar, and linear analyses of pharyngeal airway change on computed tomography and cephalometry after mandibular setback surgery. Am J Orthod Dentofacial Orthop 2010;138:292–9. 12. Riley RW, Powell NB, Guilleminault C, Ware W. Obstructive sleep apnea syndrome following surgery for mandibular prognathism. J Oral Maxillofac Surg 1987;45: 450–2. 13. Tselnik M, Pogrel MA. Assessment of the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg 2000;58:282–5. 14. Turnbull NR, Battagel JM. The effects of orthognathic surgery on pharyngeal airway dimensions and quality of sleep. J Orthod 2000;27:235–47. 15. Kempers KG, Foote JW, Brennan TD. Obesity: prevalence and considerations in oral and maxillofacial surgery. J Oral Maxillofac Surg 2000;58:137–43. 16. Ishiguro K, Kitamura N, Kobayashi T, Saito S. Relationship between severity of sleepdisordered breathing and craniofacial morphology in Japanese male patients. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;107:343–9. 17. Kitagawara K, Kobayashi T, Goto H, Yokobayashi T, Kitamura N, Saito C. Effects of mandibular setback surgery on oropharyngeal airway and arterial oxygen saturation. Int J Oral Maxillofac Surg 2008;37:328–33. 18. Kubota Y, Nakayama H, Takada T, Matsuyama N, Sakai K, Yoshizawa H, et al. Facial axis angle as a risk factor for obstructive sleep apnea. Intern Med 2005;44: 805–10. 19. Abramson ZR, Susarla S, Tagoni JR, Kaban L. Three-dimensional computed tomographic analysis of airway anatomy. J Oral Maxillofac Surg 2010;68:363–71. 20. El AS, El H, Palomo JM, Baur DA. A 3dimensional airway analysis of an obstructive sleep apnea surgical correction with cone beam computed tomography. J Oral Maxillofac Surg 2011;69:2424–36.
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21. Enciso R, Nguyen M, Shigeta Y, Ogawa T, Clark GT. Comparison of cone-beam CT parameters and sleep questionnaires in sleep apnea patients and control subjects. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109:285–93. 22. Grauer D, Cevidanes LS, Styner MA, Ackerman JL, Proffit WR. Pharyngeal airway volume and shape from cone-beam computed tomography: relationship to facial morphology. Am J Orthod Dentofacial Orthop 2009;136:805–14. 23. Park SB, Kim YI, Son WS, Hwang DS, Cho BH. Cone-beam computed tomography evaluation of short- and long-term airway change and stability after orthognathic surgery in patients with Class III skeletal deformities: bimaxillary surgery and mandibular setback surgery. Int J Oral Maxillofac Surg 2012;41:87–93. 24. Shigeta Y, Enciso R, Ogawa T, Shintaku WH, Clark GT. Correlation between retroglossal airway size and body mass index in OSA and non-OSA patients using cone beam CT imaging. Sleep Breath 2008;12: 347–52.
25. Suto Y, Matsuo T, Kato T, Hori I, Inoue Y, Ogawa S, et al. Evaluation of the pharyngeal airway in patients with sleep apnea: value of ultrafast MR imaging. Am J Roentgenol 1993;160:311–4. 26. Saigusa H, Suzuki M, Higurashi N, Kodera K. Three-dimensional morphological analyses of positional dependence in patients with obstructive sleep apnea syndrome. Anesthesiology 2009;110:885–90. 27. Sears CR, Miller AJ, Chang MK, Huang JC, Lee JS. Comparison of pharyngeal airway changes on plain radiography and conebeam computed tomography after orthognathic surgery. J Oral Maxillofac Surg 2011;69:385–94. 28. Ohdaira F, Nakamura K, Nakayama H, Satoh M, Ohdaira T, Nakamata M, et al. Demographic characteristics of 3,659 Japanese patients with obstructive sleep apnea–hypopnea syndrome diagnosed by full polysomnography: associations with apnea–hypopnea index. Sleep Breath 2007;11:93–101. 29. Kuna ST, Gurubhagavatula I, Maislin G, Hin S, Hartwig KC, McCloskey S, et al. Noninferiority of functional outcome in
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Address: Takashi Uesugi Division of Reconstructive Surgery for Oral and Maxillofacial Region Department of Tissue Regeneration and Reconstruction Niigata University Graduate School of Medical and Dental Sciences 2-5274 Gakkocho-Dori Niigata 951-8514 Japan Tel: +81 025 227 2878; Fax: +81 025 223 6516 E-mail: [email protected]
Clinical Paper Orthognathic Surgery
Effects of orthognathic surgery on pharyngeal airway and respiratory function during sleep in patients with mandibular prognathism
T. Uesugia,*, T. Kobayashia, D. Hasebea, R. Tanakab, M. Ikeb, C. Saitoa a
Division of Reconstructive Surgery for Oral and Maxillofacial Region, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan; b Division of Oral and Maxillofacial Radiology, Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
T. Uesugi, T. Kobayashi, D. Hasebe, R. Tanaka, M. Ike, C. Saito: Effects of orthognathic surgery on pharyngeal airway and respiratory function during sleep in patients with mandibular prognathism. Int. J. Oral Maxillofac. Surg. 2014; 43: 1082– 1090. # 2014 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The aim of this study was to determine changes in overnight respiratory function and craniofacial and pharyngeal airway morphology following orthognathic surgery. The subjects were 40 patients in whom mandibular prognathism was corrected by orthognathic surgery: a one-jaw operation in 22 patients and a two-jaw operation in 18 patients. Morphological changes were studied using cone beam computed tomography immediately before surgery and at more than 6 months after surgery, and the apnoea–hypopnoea index (AHI) was measured with a portable polysomnography system. Pharyngeal airway volume was decreased significantly after surgery, especially in the one-jaw operation group. AHI was not changed significantly after surgery in either group, although AHI in one patient in the one-jaw operation group was increased to 19 events/h. There was no significant change in pharyngeal airway morphology in that patient, but he was obesity class 1 and was 54 years old. In conclusion, some patients who are obese, have a large amount of mandibular setback, and/or are of relatively advanced age may develop sleep-disordered breathing after mandibular setback; a two-jaw operation should therefore be considered in skeletal class III patients who have such risks because it decreases the amount of pharyngeal airway space reduction caused by mandibular setback surgery.
Mandibular setback surgery for mandibular prognathism can reduce the space in the pharyngeal airway,1–14 and it has been suggested that it might induce sleep-disor0901-5027/0901082 + 09
dered breathing, typified by obstructive sleep apnoea syndrome (OSAS).4–6,12 We have previously reported cases in whom reduction of the pharyngeal airway space
Key words: mandibular setback surgery; jaw deformity; cone beam computed tomography; pharyngeal airway; respiratory function during sleep. Accepted for publication 23 June 2014 Available online 12 July 2014
and OSAS were caused by mandibular setback surgery.5 OSAS is a potentially life-threatening disorder caused by repetitive narrowing and obstruction of the pha-
# 2014 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Airway changes after orthognathic surgery ryngeal airway during sleep, and it has been associated with loud snoring and apnoea. OSAS is regarded as one of the risk factors of hypertension, ischaemic myocardial diseases, and cerebral vascular diseases.15 It is also thought to be one of the causes of traffic accidents. Lateral cephalograms have been used widely to evaluate craniofacial and pharyngeal airway morphology,1,2,4–9,12– 14,16–18 and lateral cephalometric measurements are useful for analyzing airway size on the sagittal plane; however, they do not accurately reflect the three-dimensional (3D) airway anatomy. Therefore, 3D imaging has been preferred in recent years for evaluating changes of the pharyngeal after orthognathic surairway gery.3,7,10,11,19–25 Conventional spiral computed tomography (CT) and magnetic resonance imaging (MRI) have been the methods of choice for obtaining 3D information on craniofacial and pharyngeal morphology,3,7,11,19,24–26 but their use is limited because of the costs and/or the greater radiation exposure. Cone beam computed tomography (CBCT) is a recently introduced technology that has been used for 3D analyses of craniofacial and pharyngeal morphology because the radiation exposure and the cost are decreased compared with those of conventional CT.10,20–23,27 We are interested in the effects of orthognathic surgery on the pharyngeal airway and respiratory function during sleep in patients with mandibular prognathism. The aim of this study was to determine whether orthognathic surgery causes OSAS with morphological changes after orthognathic surgery in patients with mandibular prognathism. In this study we investigated changes in overnight respiratory function with a portable polysomnography (PSG) system and examined 3D morphological changes in the maxillomandibular skeleton and pharyngeal airway using CBCT before and after orthognathic surgery.
A), and a combination of Le Fort I osteotomy and bilateral sagittal split osteotomy was performed in 18 patients who had mandibular prognathism combined with maxillary retrusion, asymmetry, and/or open bite (group B). None of the subjects had symptoms of OSAS such as snoring or apnoea, and no cases of cleft palate or craniofacial syndrome were included. The mean age of the subjects at surgery was 23 years (range 16–54 years). All of the subjects received pre- and postoperative orthodontic treatment, and osteosynthesis was achieved using a titanium miniplate and resorbable fixation devices. Maxillomandibular fixation was performed 1 day after surgery and was maintained for 14 days. As a control group, 16 subjects (nine males and seven females) with normal occlusion and no symptoms of sleep-disordered breathing underwent the same CBCT examinations as those performed in the patients. The mean age of the control subjects was 26 years (range 21–38 years). The study protocol was approved by the institutional ethics committee and informed consent was obtained from all subjects. Imaging procedure
All of the patients underwent CBCT examinations (CB MercuRay; Hitachi Medical Corporation, Tokyo, Japan) for assessment of craniofacial and pharyngeal morphology before surgery (T0) and at more than 6 months after surgery (mean 9 2.1 months, range 6–12 months) (T1). For the control group, two CBCT images were taken repeatedly on separate days to assess the accuracy of CBCT analyses. The subjects sat upright with the Frankfort horizontal plane parallel to the floor and with centric occlusion. CBCT data of
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the maxillofacial regions were acquired with a 0.38-mm voxel size and 512 512 matrices, using 120 kVp, 15 mA, 9.6-s scan time, and 12-inch detector field. The CBCT data were converted into DICOM (digital imaging and communication in medicine) format, and 3D images of the craniofacial and pharyngeal airway morphology were reconstructed with a 3D image analysis system (INTAGE Realia Pro; Cybernet Systems Co., Ltd, Tokyo, Japan). Since small deviations in the position of the head from ideal are bound to occur, reconstructed 3D images taken before surgery were corrected and re-aligned using the Frankfort horizontal (FH) plane (XY plane), coronal plane (XZ plane), and midsagittal plane (YZ plane) as references. The FH plane was defined by the bilateral uppermost point on the bony external auditory meatus (porion) and lowest point on the right inferior borders of the bony orbit (orbitale). The coronal plane was defined as a plane passing through bilateral porions and perpendicular to the FH plane. The midsagittal plane was defined as a vertical plane passing through the most anterior point of the frontonasal suture (nasion) and perpendicular to the FH plane and coronal plane (Fig. 1). Next, the coordinates of the 3D images obtained at more than 6 months after surgery were adjusted and conformed to the coordinates of the preoperative standardized images by superposition of four anatomical landmarks: nasion (N), posterior clinoid process (PCP), and bilateral most inferior points of the mastoid process (MsR, MsL) (Fig. 2). Measurements of skeletal changes
Unified 3D images were exported in DICOM format and imported into OsiriX (ver. 3.5.1; Pixmeo, Geneva, Switzerland)
Materials and methods
This prospective study included 40 patients (21 males and 19 females) in whom mandibular prognathism was corrected surgically during the period June 2010 to March 2012; agreement to participate in this study was obtained before surgery. There were no drop-outs. The patients were divided into two groups according to the type of orthognathic surgery done. Bilateral sagittal split osteotomies were performed in 22 patients with simple mandibular prognathism (group
Figure 1. Configurations of the three reference planes. Axial (XY) plane: Frankfort horizontal (FH) plane passing through the bilateral uppermost points on the bony external auditory meatus (porion) and lowest point on the right inferior borders of the bony orbit (orbitale). Coronal (XZ) plane: plane passing through bilateral porions and perpendicular to the FH plane. Midsagittal (YZ) plane: vertical plane passing through the most anterior point of the frontonasal suture (nasion) and perpendicular to the FH plane and coronal plane.
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Uesugi et al. part of the epiglottis. The pharyngeal airway was divided into two regions: the nasopharynx (between the upper border of the nasopharynx and PNS planes) and the oropharynx (between the PNS and lower part of the epiglottis planes) (Fig. 4). The two airway volumes were calculated from the voxel numbers of preand postoperative 3D images, and the average of the cross-sectional areas (ACSA) was calculated to exclude the influence of length of the pharyngeal airway. To evaluate the anatomical characteristics of the oropharyngeal airway, the largest transverse width (LTW), anteroposterior length (APL), and cross-sectional area (CSA) of the four axial sections (nasal, palatal, oropharyngeal, and tongue sections) were calculated from the preand postoperative 3D images (Figs. 4–7). Accuracy of CBCT analyses
this line. The pogonion was defined as the most anterior point on the osseous contour of the chin corresponding to this vertical line (Fig. 3).
All measurements were performed by a single examiner to reduce measurement errors. In order to determine the accuracy of CBCT analyses, differences in coordinate values of ANS, PNS, and pogonion between the two CBCT images taken repeatedly in the control group were examined three times and the averages of maximum differences were calculated. Differences in pharyngeal airway measurements between the two CBCT images were also calculated.
Measurements of pharyngeal airway morphology
Measurement of the apnoea–hypopnoea index (AHI)
Pharyngeal airway morphology was analyzed from the unified DICOM data by means of two 3D imaging software programs: INTAGE Realia Pro and ImageJ (ver.1.47a; National Institutes of Health, Bethesda, MD, USA). The pharyngeal airway was defined as the region between horizontal planes passing through the upper border of the nasopharynx and lower
Overnight polysomnography (PSG) using a portable PSG system (PulSleep LS-120; Fukuda Denshi Co., Ltd, Tokyo, Japan) was performed at T0 and T1. The AHI was calculated as the sum of apnoea and hypopnoea events per hour of sleep. An apnoea event was defined as the cessation of airflow for more than 10 s, and a hypopnoea event was defined as 70% of a
Figure 2. Reference points for superposition of anatomical landmarks. (A) Axial (XY) view. (B) Midsagittal (YZ) view. (C) Midsagittal (YZ) view. (D) Coronal (XZ) view. PCP: posterior clinoid process identified on axial (XY) and midsagittal (YZ) views. MsR, MsL: bilateral most inferior points of the mastoid process identified on coronal (XZ) and midsagittal (YZ) views.
to assess movement of the maxilla and mandible. Changes in coordinate values of the ANS, posterior nasal spine (PNS), and pogonion were calculated from the 3D images at T0 and T1. Positive values were assigned to anterior, inferior, and rightward movements. In this procedure, it is difficult to define the pogonion in an asymmetric case because the most anterior point on the osseous contour of the chin is changed after surgery. The pogonion was therefore determined as follows: first, a line was drawn parallel to the y-axis passing through the most anterior point on the osseous contour of the chin corresponding to mental spines in the XY plane, and then a vertical line to yaxis was drawn on the YZ plane matching
Figure 3. Reference points for analyses of skeletal changes. (A) Axial (XY) view of the maxilla. (B) Axial (XY) view of the mandible. (C) Midsagittal (YZ) view. ANS: anterior nasal spine identified on axial (XY) and midsagittal (YZ) views. PNS: posterior nasal spine identified on axial (XY) and midsagittal (YZ) views. Pogonion: most anterior point on the osseous contour of the chin identified on axial (XY) and midsagittal (YZ) views.
Airway changes after orthognathic surgery
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Figure 4. Measurement of pharyngeal airway morphology. (A) Lateral airway image obtained using a volume rendering technique. The pharyngeal airway was defined as the region between horizontal planes passing through the upper border of the nasopharynx and lower part of the epiglottis. The black rectangle indicates the measurement range. (B) Lateral view of the extracted airway. (C) Frontal view of the extracted airway. Dotted lines indicate the four axial sections for pharyngeal airway measurements: N, nasal section; P, palatal section; O, oropharyngeal section; T, tongue section.
normal breath and/or a 4% drop in SpO2 during sleep. Statistical analysis
Mean values and standard deviations were calculated for all measured parameters. Since it could not be assumed that the parameters had normal distributions, Friedman’s test was used to determine whether changes in each parameter had significance in their groups. After the significance of the parameters was proved, Wilcoxon’s matched-pair signed rank sum test was used to assess the significance of differences in paired parameters in each
group. Spearman’s correlation analysis was performed to assess the correlation between each parameter. Probabilities of less than 0.05 were accepted as significant. Data were analyzed using IBM SPSS Statistics 20 for Windows (IBM Corp., Armonk, NY, USA). Results
The mean body mass index (BMI) values of the patients at T0 and T1 were 21.1 kg/ m2 (range 15–34.4 kg/m2) and 20.9 kg/m2 (range 15.2–33.8 kg/m2), respectively. The mean BMI values in the control group at the first and second measurements were
22.1 kg/m2 (range 17.8–26.4 kg/m2) and 22.1 kg/m2 (range 17.8–26.1 kg/m2), respectively. There were no significant differences between the mean BMI values. Accuracy of CBCT analyses
The differences in coordinate values of ANS, PNS, and pogonion between the two CBCT images of the control group were in the range 0.24–0.48 mm on average, which seemed to be acceptable accuracy (Table 1). For the pharyngeal airway measurements, the differences in volumes were 0.4 to 0.1 cm3, the difference in ACSA was 0 cm2, the differences in CSA 0.07 to on four axial planes were 0.13 cm2, and the differences in LTW and APL on four axial planes were 0.8 to 0.8 mm (Table 2). Skeletal changes following orthognathic surgery
The maxilla moved in an anterosuperior direction and rotated clockwise on average in group B, and the mandible moved posterosuperiorly at pogonion on average in both groups. There was no significant difference in the amounts of mandibular movement between the two groups, although the amount of movement in group A was greater than that in group B (Table 3). Pharyngeal airway changes following orthognathic surgery
Figure 5. Four axial sections for pharyngeal airway measurements. (A) Nasal section: plane passing through the Eustachian orifice (Eo) and parallel to the FH plane. (B) Palatal section: plane passing through the PNS and parallel to the FH plane. (C) Oropharyngeal section: plane passing through the most prominent point of the palatine tonsil to the pharyngeal airway (Pt) and parallel to the FH plane. (D) Tongue section: plane passing through the most posterior point of the lingual radix (Plr) and parallel to the FH plane.
Oropharyngeal airway volume, LTW on four axial planes, and APL and CSA on two axial planes of the oropharyngeal area, were significantly decreased in group A at more than 6 months after surgery
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Uesugi et al. the pogonion was significantly correlated with reductions in the volume of the pharynx and LTW, APL, and CSA in the palatal section in group A (Table 7). In group B, the amount of superior movement at the pogonion was significantly correlated with a reduction in only CSA in the palatal section (Table 8). There was no correlation between AHI and BMI, age, or pharyngeal airway changes in either group. Discussion
Figure 6. Cross-sectional area (CSA) measurements of the pharyngeal airway. (A) Ordinal axial bone image. (B) Binarized image from which the air density area of the pharyngeal space was extracted and measured on four axial sections.
Figure 7. Linear measurements of the pharyngeal airway. (A) Anteroposterior length (APL) of the pharyngeal airway. (B) Largest transverse width (LTW) of the pharyngeal airway. APL and LTW were each measured on four axial sections.
(Table 4). In contrast, only APL of the nasal section was significantly increased in group B at more than 6 months after surgery (Table 5). Table 1. Differences in coordinate values between the two CBCT images in the control group (n = 16). Differences in coordinate values, mm ANS x-Axis y-Axis z-Axis PNS x-Axis y-Axis z-Axis Pogonion x-Axis y-Axis z-Axis
0.46 0.4 0.31 0.41 0.24 0.26 0.48 0.39 0.42
CBCT, cone beam computed tomography; ANS, anterior nasal spine; PNS, posterior nasal spine.
Measurements of AHI
There was no significant difference between AHI values before and at more than 6 months after surgery in either group, and there was no significant difference between the two groups at any stage (Table 6). One patient was diagnosed with moderate OSAS after surgery because AHI increased to 19 events/h from the preoperative 14.9 events/ h. He was a 54-year-old male with obesity class 1 (BMI of 34.4 kg/m2 before surgery and 33.8 kg/m2 more than 6 months after surgery) who underwent one-jaw surgery. He did not have subjective symptoms of OSAS before or at more than 6 months after surgery, but showed a large amount of mandibular setback at surgery (10.1 mm backward at pogonion), although there was no significant change in the pharyngeal airway.
Correlations
Spearman’s correlation analysis showed that the amount of superior movement at
Several reports have suggested that mandibular setback surgery might induce disordered breathing.4–6,9,12 Sleepdisordered breathing typified by OSAS has been identified as a major cause of sleep disturbance and is typically recognized by symptoms such as extreme daysleepiness, severe snoring, time obstruction of the pharyngeal airway, and hypoxaemia during sleep. Obstruction that causes episodes of apnoea is the result of collapse of the pharyngeal airway and usually occurs at the oropharynx or velopharynx. Genetic and environmental factors for the development of obstructive sleep apnoea have been linked to obesity, skeletal conditions such as a short mandibular body and mandibular retreat, large tongue or uvula, shape of the airway, age, and ethnicity.16,28 To prevent the development of obstructive sleep apnoea after mandibular setback, it is important to evaluate the risk and to design a plan for orthognathic surgery, which is what we have done. In this study, the effects of mandibular setback surgery on craniofacial and pharyngeal morphology and on respiratory function during sleep were investigated. Since the airway is a 3D space surrounded by soft tissues, 3D image analysis is necessary for accurate assessment. The recently introduced CBCT examination has the advantages of a lower radiation dose and lower cost than those of other CT systems such as spiral CT. Therefore, we used CBCT to quantify the 3D changes in skeletal and pharyngeal airway morphology after orthognathic surgery. The volumes of the nasopharyngeal and oropharyngeal regions, ACSA, and APL, LTW, and CSA on four axial planes, were calculated in the present study as an alternative approach to the analysis of anatomical characteristics of the pharyngeal airway. Our CBCT analysis method appears to have acceptable accuracy, although the standard deviations of the differences in CSA on each axial plane were greater than those of the other parameters.
Airway changes after orthognathic surgery Table 2. Differences in pharyngeal airway measurements between the two CBCT images in the control group (n = 16).a Volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) ACSA (cm2) Nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
First
Second
Difference
8 4.2 15.4 7.9 23.4 11.9 2.83 1.25
7.9 3.7 15.8 8.7 23.7 12.1 2.87 1.27
0.1 0.8 0.4 2.7 0.3 3 00
4.53 1.39 19.4 4.2 22.8 3.3
4.53 1.32 19.1 4.1 23 2.3
0 0.3 0.3 1.2 0.2 1.7
5.54 2.33 20.5 3.8 20.9 3.6
5.48 2.29 20.7 3.7 20.8 3.7
0.06 0.77 0.2 1.3 0 1.3
2.59 1.75 10.5 4.3 18.3 6.8
2.67 1.8 10.7 3.9 19.1 6.7
0.07 0.51 0.2 1.6 0.8 3.1
2.93 1.29 11.1 2.8 29.8 5.7
2.8 1.39 10.3 3 30.3 4.8
0.13 0.52 0.8 1.7 0.6 2.7
CBCT, cone beam computed tomography; ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Values are given as the mean standard deviation.
It appears that the cross-sectional surfaces on four axial planes of the pharyngeal airway are affected by a slight inclination of the head, because the pharyngeal airway is composed of soft tissues with complex configurations such as the soft palate, tongue base, and pharyngeal recess. On the other hand, it appears that linear measurements are almost unchanged on the same axial planes because indicators of linear measurement such as the deepest point of the pharyngeal wall do not change significantly with a slight inclination of the head. Recently, several techniques to assess 3D skeletal and pharyngeal airway Table 3. Positional changes in skeletal reference points following orthognathic surgery.a Group A (n = 22) ANS x-axis y-axis z-axis PNS x-axis y-axis z-axis Pogonion x-axis y-axis z-axis
Group B (n = 18)
– – –
0.2 0.9 0.6 1.2 0.3 0.9
– – –
0.3 0.5 2.1 0.9 1.0 1.5
1.6 2.6 4.9 2.2 1.0 1.4
1.1 4.6 3.2 3.2 1.8 2.4
ANS, anterior nasal spine; PNS, posterior nasal spine. a Values are given as the mean standard deviation, in mm.
changes after orthognathic surgery with images have been CT reported.3,7,10,11,23,27 Some authors3,7,23 have reported the pharyngeal airway space to be reduced mainly in the oropharynx region after mandibular setback surgery. Similarly, oropharynx volume, total pharynx volume, ACSA, N-LTW, P-LTW, OCSA, O-APL, O-LTW, T-CSA, T-APL,
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and T-LTW in the one-jaw surgery group were significantly decreased in the present study, though only N-APL was significantly increased in group B. On the other hand, Park et al.23 reported that there was no significant reduction in the pharyngeal airway space after mandibular setback surgery and suggested that the pharyngeal airway might transform to preserve pharyngeal airway capacity in the changed environment after mandibular setback surgery. In the present study, superior mandibular movements at the pogonion showed correlations to reductions in the pharyngeal airway mainly in the palatal section in both groups. Even though the amount of superior movements at the pogonion in group B was greater than that in group A, pharyngeal airway volume was not decreased significantly in group B. One possible reason for this is that maxillary advancement was combined with mandibular setback in group B. Several studies have shown that bimaxillary surgery diminishes the amount of pharyngeal airway reduction caused by mandibular setback surgery.2,4,9,10,23 Lee et al.10 reported that a greater clockwise rotation of the maxilla and mandible as a complex and a greater increase in the upper part (between the upper border of the nasopharynx and first cervical vertebra planes) and decrease in the lower part (between the first cervical vertebra planes and third cervical vertebra planes) of the airway,
Table 4. Results of pharyngeal airway measurements for group A (n = 22).a Volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) ACSA (cm2) Nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
T0
T1
8.6 3.4 16.5 7.5** 25.1 10.6** 3.12 1.15**
7.8 2.6 12.5 4.7** 20.3 6.8** 2.36 0.76**
3.98 0.9 18.1 3.3 23.5 2.7**
4.02 1.06 17.7 3.9 22.9 2.6**
5.21 1.71 20.3 4.1 23.8 5.3**
4.92 1.62 19.8 4.4 22.6 5.4**
3.31 1.78** 13.4 4** 19.8 6.6**
2.27 1.07** 11.3 3.3** 17.6 6.5**
2.99 1.22** 11.6 2.8* 29.8 5.5*
2.29 0.79** 10.0 2.1* 28.6 5.6*
ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Values are given as the mean standard deviation. Statistically significant difference between T0 and T1: **P < 0.01, *P < 0.05.
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Table 5. Results of pharyngeal airway measurements for group B (n = 18).a Volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) ACSA (cm2) Nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
T0
T1
6.7 2.7 14.8 5.7 21.5 7.9 2.74 0.83
7.2 2.6 14.2 6 21.3 8 2.7 0.8
3.3 0.83 16.2 3.9* 22.9 1.7
3.55 0.72 17.1 3.5* 22.7 2.1
4.19 1.66 17.4 4.9 21.5 5.5
4.49 1.3 18.9 3.4 22.6 4.9
3.02 1.48 12.6 3.9 19.5 6.9
2.79 1.23 12.2 4 18.9 7.4
2.79 1 10.9 3.4 30.5 4
2.7 0.9 10.6 3.1 30.5 3.5
ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Values are given as the mean standard deviation. Statistically significant difference between T0 and T1: *P < 0.05.
were found after bimaxillary surgery, and total airway volume was therefore not changed. In the present study, there was little increase in nasopharynx volumes because of the small amounts of anterior and superior movements of the maxilla. Full overnight PSG is important for the diagnosis of sleep-disordered breathing. However, the use of full PSG is limited because of economic and manpower problems. We used a portable PSG system, which is classified as a type III sleep monitor by the US Centers for Medicare and Medicaid Services (CMS) and the American Academy of Sleep Medicine (AASM) guidelines, for patients treated with orthognathic surgery. A portable PSG system could be useful for prompt diagnosis if we know the characteristics and weak points caused by decreased PSG parameters, especially lack of electroencephalography (EEG).29,30 Hochban et al.6 reported that there was no evidence of postoperative sleep-disordered breathing in 16 patients who underwent Table 6. Apnoea–hypopnoea index (AHI, number/h) measured with a portable polysomnography system.a Group A (n = 22) Group B (n = 18) a
T0
T1
3.1 3.2 1.9 1.7
3.4 4.1 2.2 2.1
Values are given as the mean standard deviation.
mandibular setback surgery, even though the pharyngeal airway was decreased after surgery. In a previous study by our group,5 in which 22 patients with mandibular prognathism were examined by full PSG before and 6 months after mandibular setback surgery (average 7.1 mm backward at
pogonion), AHI was not changed significantly after surgery, although two patients who underwent a large amount of mandibular setback (12.6 mm and 13.7 mm backward at pogonion) were diagnosed with mild OSAS after surgery. Similarly, in the present study using a portable PSG system, there were no significant changes in AHI and no signs of sleep-disordered breathing after surgery, although AHI in one patient was increased to 19 events/h after surgery (preoperative AHI: 14.9 events/h). In that patient, there was no significant change in pharyngeal airway, but he was obesity class 1 and was 54 years old, and he had a comparatively large amount of mandibular setback (10.1 mm backward at pogonion). In this patient, the amount of mandibular setback should have been decreased by maxillary advancement, but the patient did not accept two-jaw surgery. Several reports9,21,28 have shown ageing, obesity, and a large amount of mandibular setback to be risk factors for OSAS. In a previous study by our group,9 positive correlations between BMI and oximetry indices were found in 78 patients who underwent mandibular setback surgery. Therefore, it appears that patients who are obese, who have a large amount of mandibular setback, and/or who are of advanced age are at risk for the development of OSAS after mandibular setback surgery. Preoperative weight loss should be recommended to obese patients because orthognathic surgery is elective surgery.
Table 7. Spearman’s rank correlation coefficient between mandibular movements at pogonion and reductions in pharyngeal airway measurements for group A (n = 22).a
Reductions in volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) Reductions in ACSA (cm2) Reductions in nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Reductions in palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Reductions in oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Reductions in tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
Posterior movements at pogonion
Superior movements at pogonion
0.089 0.108 0.104 0.084
0.428* 0.494* 0.357 0.416
0.127 0.153 0.359
0.063 0.016 0.063
0.264 0.05 0.097
0.434* 0.616** 0.45*
0.224 0.165 0.387
0.391 0.454* 0.234
0.247 0.311 0.376
0.276 0.248 0.066
ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Significant difference: **P < 0.01, *P < 0.05.
Airway changes after orthognathic surgery Table 8. Spearman’s rank correlation coefficient between mandibular movements at pogonion and reductions in pharyngeal airway measurements for group B (n = 18).a
Reductions of volume Nasopharynx (cm3) Oropharynx (cm3) Total (cm3) Reductions of ACSA (cm2) Reductions of nasal section (N) N-CSA (cm2) N-APL (mm) N-LTW (mm) Reductions of palatal section (P) P-CSA (cm2) P-APL (mm) P-LTW (mm) Reductions of oropharyngeal section (O) O-CSA (cm2) O-APL (mm) O-LTW (mm) Reductions of tongue section (T) T-CSA (cm2) T-APL (mm) T-LTW (mm)
Posterior movements at pogonion
Superior movements at pogonion
0.179 0.022 0.263 0.191
0.379 0.35 0.275 0.381
0.23 0.275 0.243
0.21 0.025 0.175
0.166 0.199 0.014
0.583* 0.273 0.353
0.292 0.12 0.11
0.323 0.367 0.29
0.125 0.049 0.044
0.073 0.251 0.07
ACSA, average of the cross-sectional areas; CSA, cross-sectional area; APL, anteroposterior length; LTW, largest transverse width. a Significant difference: *P < 0.05.
In conclusion, there was no evidence of sleep-disordered breathing after mandibular setback surgery. However, patients with certain risk factors such as obesity, a large amount of mandibular setback, and/or advanced age may develop sleepdisordered breathing after mandibular setback surgery. In such patients, it might be better to consider a combination of Le Fort I osteotomy and bilateral sagittal split osteotomy to reduce the narrowing of the pharyngeal airway, and careful attention should be paid to respiratory function during sleep after surgery. Funding
None. Competing interests
None declared. Ethical approval
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Address: Takashi Uesugi Division of Reconstructive Surgery for Oral and Maxillofacial Region Department of Tissue Regeneration and Reconstruction Niigata University Graduate School of Medical and Dental Sciences 2-5274 Gakkocho-Dori Niigata 951-8514 Japan Tel: +81 025 227 2878; Fax: +81 025 223 6516 E-mail: [email protected]