CRANIOMAXILLOFACIAL DEFORMITIES/COSMETIC SURGERY
Does the Pharyngeal Airway Recover After Sagittal Split Ramus Osteotomy for Mandibular Prognathism? Jae-Yun Jeon, DDS,* Tae-Sun Kim, DDS,y Sang Yoon Kim, DMD, MD,z Chang-Joo Park, DDS, PhD,x and Kyung-Gyun Hwang, DDS, PhDk Purpose:
Mandibular setback surgery can adversely affect the pharyngeal airway. The aim of this study was to investigate changes of the pharyngeal airway at specific intervals during a 12-month period after bilateral sagittal split ramus osteotomy (BSSO) for correction of mandibular prognathism.
Materials and Methods:
This retrospective cohort study included patients with mandibular prognathism who underwent BSSO. The pharyngeal airway was measured at 3 different levels on lateral cephalograms: the uvula tip, the most inferior-anterior point on the body of the second cervical vertebra (low-C II), and a midanterior point on the body of the third cervical vertebra (mid-C III). The pharyngeal airway was measured preoperatively, immediately postoperatively, and 1, 3, 6, and 12 months postoperatively. The measurements at each level were compared. Multivariable analysis of variance was used to measure the changes in pharyngeal airway space over time.
Results:
The study sample was composed of 30 patients (14 men and 16 women) who were diagnosed with mandibular prognathism. The pharyngeal airway at the uvular tip level was significantly reduced by 39% (P < .001) after surgery and was significantly improved by 26% (P < .01) from baseline at 1 month postoperatively. The pharyngeal airway at the low-C II level was significantly reduced by 27% (P < .001) after surgery and was significantly improved by 24% (P < .01) from baseline at 1 month postoperatively. The pharyngeal airway at the mid-C III level was significantly reduced by 23% (P < .001) after surgery and was improved by only 13% from baseline at 1 month postoperatively. Additional statistical changes were not noted on 3 and 6 months postoperative radiographs at all levels. The pharyngeal airway was decreased by 16, 19, and 8% from baseline at 12 months postoperatively, respectively. The upper airway length was significantly increased immediately after surgery (P < .001), but was incompletely recovered at 12 months postoperatively. Conclusion:
The outcomes of this study indicate that the pharyngeal airway gradually recovers over time. An immediate postoperative reduction in pharyngeal airway space can induce or exacerbate obstructive sleep apnea symptoms; thus, any pre-existing symptoms should be screened and considered for surgical treatment planning. Ó 2015 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg -:1-8, 2015
*Clinical
Lecturer,
Department
of
Dentistry/Oral
and
Jae-Yun Jeon and Tae-Sun Kim contributed equally to this work.
Maxillofacial Surgery, College of Medicine, Hanyang University,
This work was supported by a research grant from Hanyang
Seoul, Korea.
University (HY-2011-MC).
yPhD Candidate, Department of Dentistry/Oral and Maxillofacial
Address correspondence and reprint requests to Prof Hwang:
Surgery, College of Medicine, Hanyang University, Seoul; Private
Department of Dentistry/Oral and Maxillofacial Surgery, College of
Practice, Gimpo, Gyeonggi, Korea.
Medicine, Hanyang University, 222 Wangsimni-ro, Seongdong-gu,
zFormer Chief Resident, Department of Oral and Maxillofacial
133-791, Seoul, Republic of Korea; e-mail: [email protected]
Surgery, Massachusetts General Hospital, Harvard Medical School, Boston; Private Practice, Vienna, VA. xAssociate
Professor,
Department
of
Dentistry/Oral
Received February 16 2015 Accepted May 19 2015 Ó 2015 American Association of Oral and Maxillofacial Surgeons
and
Maxillofacial Surgery, College of Medicine, Hanyang University,
0278-2391/15/00613-8
Seoul, Korea.
http://dx.doi.org/10.1016/j.joms.2015.05.028
kProfessor, Department of Dentistry/Oral and Maxillofacial Surgery, College of Medicine, Hanyang University, Seoul, Korea.
1
2 Mandibular setback is a common surgical procedure to correct dentofacial deformities. Previous studies have shown that retro-positioning of the mandible affects the facial profile and soft tissues, including the pharyngeal airway space.1-3 These studies of bilateral sagittal split ramus osteotomy (BSSO) also have shown posterior-inferior displacement of the hyoid bone and of the tongue in a similar direction.1,2,4,5 Mandibular setback osteotomy can cause narrowing of the pharyngeal airway space that resolves over time, but does not fully recover during followup.2,3,6-8 Cephalograms are standard radiographs used in maxillofacial deformity analysis and orthodontic diagnosis. The lateral cephalogram has been used for its simplicity and economical measurement of the pharyngeal airway.1-4,7,8 However, pharyngeal airway measurements can be affected by the head position at cephalometric analysis. The pharyngeal airway widens anteroposteriorly when the neck is extended and narrows when the neck is flexed. Thus, variations in head posture need to be standardized when comparing data because the results will be unreliable; to obtain accurate and precise measurements of successive changes of the pharyngeal airway, cephalometric analyses should be corrected for craniocervical inclination.9 Several studies have reported that the pharyngeal airway is reduced after mandibular setback surgery.2,3,6-8,10-12 In contrast, Eggensperger et al4 reported the size of pharyngeal airway remains unchanged in the lower portion. In addition, previous studies have reported only short-term changes in the pharyngeal airway after setback surgery1,12 and at longer intervals of 6 months and 1.5 or 2 years postoperatively.2,3,11 Previous studies have not provided specific data on postoperative change patterns of the pharyngeal airway during shorter intervals. There is no consensus on the patterns and tendencies of airway changes after setback surgery. The purpose of this study was to investigate the changes and recovery patterns of the pharyngeal airway during specific postoperative intervals up to 1 year after BSSO for correction of mandibular prognathism. The authors hypothesized that an immediate reduction in airway space postoperatively would recover slowly in proportion to the predictor variable (time) with an incomplete recovery to its original dimension. The specific aims of this study were to measure the pharyngeal airway corrected for head position variations on lateral cephalograms immediately after and at 1, 3, 6, and 12 months after mandibular setback surgery at 3 levels and to compare the pharyngeal airway at each postoperative interval.
PHARYNGEAL AIRWAY RECOVERY AFTER BSSO SETBACK
Materials and Methods STUDY DESIGN
To address the study purpose, the authors designed and implemented a retrospective cohort study and it was granted an exemption in writing by the institutional review board of Hanyang University (Seoul, Korea). The study population was composed of all patients who presented for evaluation and management of dentofacial deformities at the Department of Oral and Maxillofacial Surgery, Hanyang University Hospital from January 1, 2005 through December 31, 2012. To investigate patterns of change of the pharyngeal airway after mandibular setback, this study included only patients who underwent BSSO with a diagnosis of mandibular prognathism and had a normal anteroposterior position of the maxilla at cephalometric measurements and clinical examination. Patients were excluded if they were undergoing combined procedures (Le Fort I osteotomy and genioplasty), had facial asymmetry, had mandibular prognathism associated with craniofacial syndrome (acromegaly syndrome), and were older than 40 years. Also excluded were patients who failed to present for regular follow-up visits and postoperative radiographic studies at any of the defined intervals. STUDY VARIABLES
The primary predictor variable of this study was time. Cephalograms of all patients were taken 6 times: preoperatively, immediately postoperatively, and 1, 3, 6, and 12 months postoperatively. The primary outcome variable of this study was the pharyngeal airway measurement at each interval on cephalograms. The secondary outcome was upper airway length (from the end of the hard palate to the superoposterior area of the hyoid bone) at each interval on cephalograms. Other variables, such as age, gender, and mandibular setback amount by BSSO, also were examined. DATA COLLECTION METHODS
Lateral cephalograms were taken using a standardized technique: the tongue was in a relaxed position; the mandible was in centric occlusion; breathing was through the nose in a relaxed tidal fashion after swallowing once; and the breath was held at the end of the expiratory phase. The distance from the anode to the patient’s midsagittal plane was 150 cm and the distance from the midsagittal plane to the film was 15 cm. All lateral cephalometric radiographs were taken (Orthophos/3C, Siemens, Munich, Germany) and traced using cephalometric landmarks. The linear and angular items were measured, and the landmarks used are shown in Figure 1. First, the
3
JEON ET AL
FIGURE 1. Landmarks shown on lateral cephalogram. Cervical line, line connecting the posterior tangent to the second, third, and fourth cervical vertebra; craniocervical inclination, angle between the Na-S and the cervical line; Frankfort line, line connecting the uppermost point of the external auditory canal to the lowermost point of the orbital rim; level of the most inferior-anterior point on the body of the second cervical vertebra, distance from CV2ia to the posterior wall of the pharyngeal airway parallel to the Frankfort line; level of the midanterior point on the body of the third cervical vertebra, distance from CV3ma to the posterior wall of the pharyngeal airway parallel to the Frankfort line; Na-S, line connecting the midpoint of the pituitary fossa to the nasion; UT level, distance from the UT to the posterior wall of the pharyngeal airway parallel to the Frankfort line. CV2ia, the most inferior-anterior point on the body of the second cervical vertebra; CV2ip, the most inferior-posterior point on the body of the second cervical vertebra; CV3ma, the midanterior point on the body of the third cervical vertebra; CV4ip, the most inferiorposterior point on the body of the fourth cervical vertebra; Na, nasion; Or, orbitale; Po, porion; S, sella turcica; UT, uvular tip. Jeon et al. Pharyngeal Airway Recovery After BSSO SETBACK. J Oral Maxillofac Surg 2015.
Frankfort horizontal line that connects the uppermost point of the external auditory canal with the lowermost point of the inferior orbital rim was marked. Second, the pharyngeal airway distance parallel to the Frankfort horizontal line at 3 levels was measured: the uvula tip, the most inferior-anterior point on the body of the second cervical vertebra (low-C II level), and a midanterior point on the body of the third cervical vertebra (mid-C III level). Also, the angle of the craniocervical inclination was measured to compensate for the effect of variable head postures on the pharyngeal airway space, according to a method adopted from Anegawa et al.9
Briefly, the angle was measured using 2 lines: one connecting the midpoint of the pituitary fossa to the nasion and the other connecting the posterior tangent to the second, third, and fourth cervical vertebrae. Third, the actual pharyngeal airway measurements were corrected using 2 equations. The corrected value of the pharyngeal airway space was calculated with an actual measurement + 0.37 (100.9 angle of craniocervical inclination) for men and an actual measurement + 0.33 (103.5 angle of craniocervical inclination) for women.9 Patients who failed to present for follow-up postoperative radiographs were excluded.
4
PHARYNGEAL AIRWAY RECOVERY AFTER BSSO SETBACK
Table 1. PATIENT DEMOGRAPHICS
Demographic
Value
Age (yr) Mean SD Range Gender, n Men Women Setback (mm) Mean SD Range
23.3 5.48 17-39 30 14 16 8.43 3.36 3-18
was 12.80 3.87 mm (mean standard deviation) preoperatively (Table 2). As presented in Tables 2 and 3, the immediate postoperative pharyngeal airway space was significantly reduced to 8.01 3.78 mm (P < .001), or 61% of its preoperative value. The pharyngeal airway space was significantly recovered to 9.49 3.77 mm, or 74% of its preoperative value, by 1 month after surgery (P < .05). Further statistical changes were not noted 3 and 6 months postoperatively. The pharyngeal airway space recovered to 10.68 3.23 mm, or 84% of its preoperative value, after 12 months. PHARYNGEAL AIRWAY SPACE CHANGES AT LOW-C II LEVEL
Abbreviation: SD, standard deviation. Jeon et al. Pharyngeal Airway Recovery After BSSO SETBACK. J Oral Maxillofac Surg 2015.
STATISTICAL ANALYSES
All statistical analyses were performed using SPSS 20 (SPSS, Inc, Chicago, IL). The normality test was performed and then multivariable analysis of variance was used to measure changes of the pharyngeal airway space over time. Statistical significance was established at the 3 levels as P values less than .05, .01, and .001, respectively.
Results A total of 136 patients underwent BSSO from January 1, 2005 through December 31, 2012. Thirty adult patients met the inclusion criteria during the study period. The mean age was 23.4 years (range, 17 to 39 yr) and 14 patients were men and 16 patients were women. The average amount of surgical setback was 8.43 mm (range, 3 to 18 mm; Table 1). PHARYNGEAL AIRWAY SPACE CHANGES AT UVULAR TIP LEVEL
The measurement values corresponding to time are presented in Table 2. The pharyngeal airway space value
The measurement values corresponding to time are presented in Table 2. The pharyngeal airway value was 13.42 4.07 mm preoperatively (Table 2). As presented in Tables 2 and 3, the immediate postoperative pharyngeal airway was significantly reduced to 9.88 4.17 mm (P < .001), or 73% of its preoperative value. The pharyngeal airway space was significantly recovered to 9.93 3.97 mm, or 76% of its preoperative value, by 1 month after surgery (P < .05) and remained constant thereafter. The pharyngeal airway recovered to 10.82 3.50 mm, or 81% of its preoperative value, after 12 months. PHARYNGEAL AIRWAY SPACE CHANGES AT MID-C III LEVEL
The measurement values corresponding to time are presented in Table 2. The pharyngeal airway value was 12.92 3.57 mm preoperatively (Table 2). As presented in Tables 2 and 3, the immediate postoperative pharyngeal airway space was significantly reduced to 9.83 3.95 mm (P < .001), or 77% of its preoperative value. The pharyngeal airway space was recovered to 10.53 3.19 mm after 1 month, or 87% compared with the preoperative pharyngeal airway space
Table 2. SUCCESSIVE CHANGES OF THE PHARYNGEAL AIRWAY SPACE AND UAL AFTER BILATERAL SAGITTAL SPLIT RAMUS OSTEOTOMY
Airway Level Time PreOP (mm) PostOP (mm) M1 (mm) M3 (mm) M6 (mm) M12 (mm)
UT, Mean SD
CV2ia, Mean SD
CV3ma, Mean SD
UAL, Mean SD
12.80 3.87 8.01 3.78 9.49 3.77 9.60 3.94 9.69 4.00 10.68 3.23
13.42 4.07 9.88 4.17 9.93 3.97 9.83 3.76 10.28 4.04 10.82 3.50
12.92 3.57 9.83 3.95 10.53 3.19 10.57 3.64 11.08 2.88 11.48 2.80
64.06 6.17 73.64 7.79 67.10 7.04 65.60 6.94 66.44 5.64 66.72 6.38
Abbreviations: CV2ia, most inferior-anterior point on the body of the second cervical vertebra; CV3ma, midanterior point on the body of the third cervical vertebra; M1, 1 month after surgery M3, 3 months after surgery; M6, 6 months after surgery; M12, 12 months after surgery; PostOP, immediately after surgery; PreOP, before surgery; SD, standard deviation; UAL, upper airway length; UT, uvular tip. Jeon et al. Pharyngeal Airway Recovery After BSSO SETBACK. J Oral Maxillofac Surg 2015.
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JEON ET AL
Table 3. SUCCESSIVE CHANGES OF THE PHARYNGEAL AIRWAY SPACE AFTER BILATERAL SAGITTAL SPLIT RAMUS OSTEOTOMY BY MULTIVARIABLE ANALYSIS OF VARIANCE
T0-T1 T1-T2 T2-T3 T3-T4 T4-T5
UT
CV2ia
CV3ma
.0002z .015* NS NS NS
.0002z .004y NS NS NS
.0002z NS NS NS NS
Abbreviations: CV2ia, most inferior-anterior point on the body of the second cervical vertebra; CV3ma, midanterior point on the body of the third cervical vertebra; NS, not significant; T0-T1, before surgery to shortly after surgery; T1-T2, shortly after to 1 month after surgery; T2-T3, 1 to 3 months after surgery; T3-T4, 3 to 6 months after surgery; T4-T5, 6 to 12 months after surgery; UT, uvular tip. * Significant at P < .05. y Significant at P < .01. z Significant at P < .001. Jeon et al. Pharyngeal Airway Recovery After BSSO SETBACK. J Oral Maxillofac Surg 2015.
measurement, but it was not statistically meaningful. The pharyngeal airway reached 92% of its preoperative value at 12 months after BSSO. UPPER AIRWAY LENGTH CHANGES AT EACH INTERVAL
The measurement values corresponding to time are presented in Table 2. The upper airway length was 64.06 6.17 mm preoperatively (Table 2). As presented in Table 2, the immediate postoperative upper airway length was significantly increased to 73.64 7.79 mm (P < .001). The upper airway length was significantly recovered to 67.10 7.04 mm by 1 month after surgery (P < .001), 65.60 6.94 mm by 3 months after surgery (P < .01), and 66.44 5.84 mm by 6 months after surgery (P < .001). The upper airway length recovered to 66.72 6.38 mm after 12 months (P < .001).
Discussion The purpose of study was to investigate the pharyngeal airway space changes and recovery patterns during specific postoperative intervals up to 1 year after BSSO for mandibular prognathism. The authors hypothesized that an immediate reduction in airway postoperatively would recover slowly in proportion to time. The specific aim of this study was to measure and compare the pharyngeal airway on preoperative lateral cephalograms with postoperative cephalograms immediately and 1, 3, 6, and 12 months after mandibular setback surgery.
The results of this study confirmed the hypothesis that the pharyngeal airway decreased importantly at all 3 levels immediately after BSSO. This reduction in pharyngeal airway showed an appreciable recovery after 1 month. However, a full recovery was not achieved at 12 months postoperatively. These findings concur with previous studies that have reported incomplete recovery of the pharyngeal airway space after BSSO.2-4,7,8,11 The authors observed that the amount of recovery was different at each time point and was not proportional to time. The pharyngeal airway space was quickly recovered at 1 month, followed by a slower recovery rate during the subsequent 11 months. The rapid change of the pharyngeal airway space took place early in the postoperative phase. Thus, close observation of a patient’s airway for any new signs and symptoms of upper airway obstruction is warranted during this early postoperative period. There are controversies on the amount of pharyngeal airway space changes occurring in surgical patients with mandibular prognathism. Enacar et al13 reported that narrowing persisted from 6 months to 1 year during the average evaluation period. Conversely, Athanasiou et al14 found that the pharyngeal airway recovered by physiologic readaptation within 1 year of mandibular setback surgery. Mao et al15 reported that airway width and area increased during follow-up, but did not return to their original values. The present study identified the recovery patterns of the pharyngeal airway to approximately 74 to 87% from baseline at 1 month postoperatively after correction of mandibular prognathism using BSSO. The pharyngeal airway recovered shortly after surgical repositioning of the mandible. Although complete recovery of the pharyngeal airway was not achieved within 1 year, it is suggested that continuous adaptation occurred to 84, 81, and 92% from baseline, respectively. A long-term follow-up study is warranted to investigate the timing and possibility of full recovery. Therefore, potential incomplete recovery of the pharyngeal airway should be considered, and preoperative signs and symptoms of airway obstruction should be assessed while making a surgical treatment plan for patients with mandibular prognathism. The pharynx is anatomically divided into 3 sections: the nasopharynx (the space between the nose and the soft palate), the oropharynx (the space behind the oral cavity), and the hypopharynx (the space behind the inferior line of the epiglottis).16 The oropharynx includes the part below the soft palate and the posterior tongue,16 and this is the region examined in most studies for the relation between mandibular setback and the pharyngeal airway.13 In the present study, the change patterns of the pharyngeal airway at 12 months after BSSO were similar at all 3 levels, presumably because all levels are in the same
6 oropharyngeal airway. This concurs with the outcome of computed tomographic (CT) studies, which showed only partial recovery of the pharyngeal airway space by 2 to 3 months after surgery.10,12 The upper airway was most reduced postoperatively according to the present findings.17 Riley and Powell18 reported an important correlation between pharyngeal airway measurements on cephalograms and airway volume calculated on CT scans. After mandibular setback surgery, the tongue was the most affected structure in the oral cavity. The pharyngeal airway can be affected mostly by changes in the positions of the hyoid bone, tongue, and soft palate. Therefore, the oropharynx is the most affected region compared with the nasopharynx and hypopharynx.19 Some studies have reported changes in the position of the hyoid bone and reductions in retrolingual and hypopharyngeal airway dimensions after surgery.4,14 Tselnik and Pogrel2 reported a reduction of the retrolingual airway by 28% in length and 12.8% in volume. Posteroinferior displacement of the hyoid bone after surgery, resulting in movement of the tongue in the same direction, also has been reported; the posteriorly displaced tongue can narrow the retrolingual dimension and decrease the pharyngeal airway space.10 The present finding concurs with previous studies reporting the posteroinferior position change of the hyoid bone after BSSO when comparing upper airway length measurements at preoperative and postoperative intervals.2,10 CT scanning is recommended for evaluating volume changes and has been used in many studies. However, CT scanning has its own limitation of capturing a dynamic airway volume with a static series of radiographic images, and the risks from a large amount of radiation exposure to patients do not justify a periodic CT scan for airway measurements and evaluation. Hence, the present study was based on cephalography, which is simple, inexpensive, and noninvasive and causes less discomfort to patients. In addition, all landmarks can be easily located, including the anteroposterior extension of the pharyngeal airway. Cephalographic analysis is not without limitations because a patient’s head posture and mandibular movement can be affected by swallowing. Therefore, the head position of patients should be standardized because the pharyngeal airway space widens when the neck is extended and narrows when it is flexed. When the neck is extended and the craniocervical inclination is increased by 10 , the pharyngeal airway also increases by 3.7 mm in men and 3.3 mm in women.9 In the present study, a corrected pharyngeal airway value was calculated to compensate for variations in head position. Obstructive sleep apnea (OSA) is caused by recurrent upper airway obstructions during the sleep cycle
PHARYNGEAL AIRWAY RECOVERY AFTER BSSO SETBACK
and manifests as loud snoring, arterial oxygen desaturation, sleep fragmentation, and excessive daytime somnolence.20-22 OSA affects 2 to 4% of the general adult population and might be even more frequent in specific subgroups of patients with hypertension or heart failure.20-22 Studies have suggested craniofacial variations for patients with OSA. Some features described are a decreased cranial base length, mandibular or bimaxillary deficiency, increased lower face height, elongated soft palate, large tongue, and inferior positioning of the hyoid bone.23,24 Anatomic narrowing of the upper airway as a result of alterations in craniofacial morphology have been suggested as the cause of OSA.24,25 The size of the pharyngeal airway has received much attention because snoring and sleep apnea are closely linked to each other.5,26 A reduced pharyngeal airway can be found in various circumstances, including obesity, hypertrophic tonsil, adenoid vegetation, a large tongue, and a small jaw. If the pharyngeal airway space narrows, then resistance to airflow increases and this increases the risk of snoring and OSA.2 There is much evidence for an association between the pharyngeal airway and OSA. Riley and Powell18 showed that a pharyngeal airway smaller than 11 mm and a mandibular planeto-hyoid distance longer than 15.4 mm are indicative of OSA. Partinen et al27 reported that patients with a pharyngeal airway smaller than 5.0 mm (base of tongue level) and a mandibular plane-to-hyoid distance longer than 24.0 mm had the highest respiratory disturbance index. Muto et al28 also found a meaningful correlation between the pharyngeal airway and the position of the maxilla, mandible, and soft palate. Thus, it is believed that any alteration of the facial skeleton that replicates these features can increase airway resistance. In the present study, the pharyngeal airway space was reduced 74 to 87% of its original value immediately after mandibular setback surgery. This change can be important if patients have preexisting undiagnosed OSA symptoms. Mandibular prognathism can be corrected by mandibular setback surgery or mandibular setback in conjunction with maxillary advancement. Maxillomandibular advancement, which enlarges the pharyngeal airway, has proved to be a very effective surgical treatment modality for severe OSA.29,30 In a comparative study, bimaxillary surgery reduced the retropalatal dimension, but the effects were not important after 2 years and had much smaller effects than that of mandibular setback alone.3 Thus, bimaxillary surgery rather than mandibular setback surgery alone is preferable for correcting Class III deformities and preventing narrowing of the pharyngeal airway space, a possible predisposing factor for OSA.12 A large mandibular setback might inhibit biological
JEON ET AL
adaptation and can cause sleep-disordered breathing; thus, simultaneous maxillary advancement to minimize the amount of mandibular setback for patients with large anteroposterior discrepancies should be considered.17 This study was composed of Korean patients who had undergone BSSO alone to set back the mandible for correction of mandibular prognathism. In most Asian countries such as Korea, mandibular setback surgery is performed routinely for correction of mandibular prognathism31 and to improve facial contour esthetics. In this respect, data on pharyngeal airway change patterns after mandibular setback surgery would be beneficial to surgeons who are planning BSSO as a surgical modality. The authors confirmed the gradual recovery of the pharyngeal airway over time after BSSO through this study. However, a limitation of this study was a lack of a systematic preoperative evaluation of airway and OSA symptoms with polysomnography or an evaluation of airway dimension using CT scanning at preand postoperative intervals for comparison. Another limitation of this study was not accounting for the degrees of airway improvement associated with weight loss postoperatively. There are other important factors associated with reduction of the pharyngeal airway, such as the position of the hyoid bone and the soft tissue condition during adaptation. Further studies and evaluations related to these various factors should be conducted. Appreciably reduced pharyngeal airway on radiographs immediately postoperatively mostly recovered within 1 month after BSSO followed by a gradual recovery after 3 months. However, full recovery of the pharyngeal airway was not obtained at 12 months postoperatively. Therefore, an increased risk of postoperative airway narrowing and obstruction should be considered before treatment planning for patients undergoing mandibular setback surgery. Research is necessary to evaluate the correlation of amount of setback and its relevance to OSA symptoms.
References 1. Demetriades N, Chang DJ, Laskarides C, et al: Effects of mandibular retropositioning, with or without maxillary advancement, on the oro-naso-pharyngeal airway and development of sleeprelated breathing disorders. J Oral Maxillofac Surg 68:2431, 2010 2. Tselnik M, Pogrel MA: Assessment of the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg 58:282, 2000 3. Chen F, Terada K, Hanada K, Saito I: Predicting the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg 63:1509, 2005 4. Eggensperger N, Smolka W, Iizuka T: Long-term changes of hyoid bone position and pharyngeal airway size following mandibular setback by sagittal split ramus osteotomy. J Craniomaxillofac Surg 33:111, 2005 5. Lye KW: Effect of orthognathic surgery on the posterior airway space (PAS). Ann Acad Med Singapore 37:677, 2008
7 6. Liukkonen M, Vahatalo K, Peltomaki T, et al: Effect of mandibular setback surgery on the posterior airway size. Int J Adult Orthodon Orthognath Surg 17:41, 2002 7. Hochban W, Schurmann R, Brandenburg U, et al: Mandibular setback for surgical correction of mandibular hyperplasia— Does it provoke sleep-related breathing disorders? Int J Oral Maxillofac Surg 25:333, 1996 8. Muto T, Yamazaki A, Takeda S, et al: Accuracy of predicting the pharyngeal airway space on the cephalogram after mandibular setback surgery. J Oral Maxillofac Surg 66:1099, 2008 9. Anegawa E, Tsuyama H, Kusukawa J: Lateral cephalometric analysis of the pharyngeal airway space affected by head posture. Int J Oral Maxillofac Surg 37:805, 2008 10. Kawamata A, Fujishita M, Ariji Y, et al: Three-dimensional computed tomographic evaluation of morphologic airway changes after mandibular setback osteotomy for prognathism. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 89:278, 2000 11. Kim JS, Kim JK, Hong SC, et al: Pharyngeal airway changes after sagittal split ramus osteotomy of the mandible: A comparison between genders. J Oral Maxillofac Surg 68:1802, 2010 12. Degerliyurt K, Ueki K, Hashiba Y, et al: 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 105:495, 2008 13. Enacar A, Aksoy AU, Sencift Y, et al: Changes in hypopharyngeal airway space and in tongue and hyoid bone positions following the surgical correction of mandibular prognathism. Int J Adult Orthodon Orthognath Surg 9:285, 1994 14. Athanasiou AE, Toutountzakis N, Mavreas D, et al: Alterations of hyoid bone position and pharyngeal depth and their relationship after surgical correction of mandibular prognathism. Am J Orthod Dentofacial Orthop 100:259, 1991 15. Mao C, Aruga S, Matsuura M, et al: Changes in airway space following mandibular setback using sagittal split osteotomy and rigid internal fixation. Chin Med Sci J 12:96, 1997 16. Swartz MH: The oral cavity and pharynx, in Swartz MH (ed): Textbook of Physical diagnosis (ed 7). Philadelphia, PA, Saunders Elsevier, 2014, p 278 17. Hasebe D, Kobayashi T, Hasegawa M, et al: Changes in oropharyngeal airway and respiratory function during sleep after orthognathic surgery in patients with mandibular prognathism. Int J Oral Maxillofac Surg 40:584, 2011 18. Riley RW, Powell NB: Maxillofacial surgery and obstructive sleep apnea syndrome. Otolaryngol Clin North Am 23:809, 1990 19. Kim NR, Kim YI, Park SB, et al: Three dimensional cone-beam CT study of upper airway change after mandibular setback surgery for skeletal Class III malocclusion patients. Korean J Orthod 40: 145, 2010 20. Young T, Palta M, Dempsey J, et al: The occurrence of sleepdisordered breathing among middle-aged adults. N Engl J Med 328:1230, 1993 21. Leung RS, Bradley TD: Sleep apnea and cardiovascular disease. Am J Respir Crit Care Med 164:2147, 2001 22. Naughton MT: Sleep disorders in patients with congestive heart failure. Curr Opin Pulm Med 9:453, 2003 23. Bacon WH, Turlot JC, Krieger J, et al: Cephalometric evaluation of pharyngeal obstructive factors in patients with sleep apneas syndrome. Angle Orthod 60:115, 1990 24. Battagel JM, L’Estrange PR: The cephalometric morphology of patients with obstructive sleep apnoea (OSA). Eur J Orthod 18:557, 1996 25. Shelton KE, Woodson H, Gay S, et al: Pharyngeal fat in obstructive sleep apnea. Am Rev Respir Dis 148:462, 1993 26. Ikeda K, Ogura M, Oshima T, et al: Quantitative assessment of the pharyngeal airway by dynamic magnetic resonance imaging in obstructive sleep apnea syndrome. Ann Otol Rhinol Laryngol 110:183, 2001 27. Partinen M, Guilleminault C, Quera-Salva MA, et al: Obstructive sleep apnea and cephalometric roentgenograms. The role of anatomic upper airway abnormalities in the definition of abnormal breathing during sleep. Chest 93:1199, 1988 28. Muto T, Yamazaki A, Takeda S, et al: Relationship between the pharyngeal airway space and craniofacial morphology, taking
8 into account head posture. Int J Oral Maxillofac Surg 35:132, 2006 29. Fairburn SC, Waite PD, Vilos G, et al: Three-dimensional changes in upper airways of patients with obstructive sleep apnea following maxillomandibular advancement. J Oral Maxillofac Surg 65:6, 2007
PHARYNGEAL AIRWAY RECOVERY AFTER BSSO SETBACK 30. Prinsell JR: Maxillomandibular advancement surgery for obstructive sleep apnea syndrome. J Am Dent Assoc 133:1489, 2002 31. Chang-Hwan L, Sang-Han L, Hyun-Soo K, et al: Analysis of familial tendency in skeletal Class III malocclusion. J Korean Assoc Oral Maxillofac Surg 32:506, 2006
Does the Pharyngeal Airway Recover After Sagittal Split Ramus Osteotomy for Mandibular Prognathism? Jae-Yun Jeon, DDS,* Tae-Sun Kim, DDS,y Sang Yoon Kim, DMD, MD,z Chang-Joo Park, DDS, PhD,x and Kyung-Gyun Hwang, DDS, PhDk Purpose:
Mandibular setback surgery can adversely affect the pharyngeal airway. The aim of this study was to investigate changes of the pharyngeal airway at specific intervals during a 12-month period after bilateral sagittal split ramus osteotomy (BSSO) for correction of mandibular prognathism.
Materials and Methods:
This retrospective cohort study included patients with mandibular prognathism who underwent BSSO. The pharyngeal airway was measured at 3 different levels on lateral cephalograms: the uvula tip, the most inferior-anterior point on the body of the second cervical vertebra (low-C II), and a midanterior point on the body of the third cervical vertebra (mid-C III). The pharyngeal airway was measured preoperatively, immediately postoperatively, and 1, 3, 6, and 12 months postoperatively. The measurements at each level were compared. Multivariable analysis of variance was used to measure the changes in pharyngeal airway space over time.
Results:
The study sample was composed of 30 patients (14 men and 16 women) who were diagnosed with mandibular prognathism. The pharyngeal airway at the uvular tip level was significantly reduced by 39% (P < .001) after surgery and was significantly improved by 26% (P < .01) from baseline at 1 month postoperatively. The pharyngeal airway at the low-C II level was significantly reduced by 27% (P < .001) after surgery and was significantly improved by 24% (P < .01) from baseline at 1 month postoperatively. The pharyngeal airway at the mid-C III level was significantly reduced by 23% (P < .001) after surgery and was improved by only 13% from baseline at 1 month postoperatively. Additional statistical changes were not noted on 3 and 6 months postoperative radiographs at all levels. The pharyngeal airway was decreased by 16, 19, and 8% from baseline at 12 months postoperatively, respectively. The upper airway length was significantly increased immediately after surgery (P < .001), but was incompletely recovered at 12 months postoperatively. Conclusion:
The outcomes of this study indicate that the pharyngeal airway gradually recovers over time. An immediate postoperative reduction in pharyngeal airway space can induce or exacerbate obstructive sleep apnea symptoms; thus, any pre-existing symptoms should be screened and considered for surgical treatment planning. Ó 2015 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg -:1-8, 2015
*Clinical
Lecturer,
Department
of
Dentistry/Oral
and
Jae-Yun Jeon and Tae-Sun Kim contributed equally to this work.
Maxillofacial Surgery, College of Medicine, Hanyang University,
This work was supported by a research grant from Hanyang
Seoul, Korea.
University (HY-2011-MC).
yPhD Candidate, Department of Dentistry/Oral and Maxillofacial
Address correspondence and reprint requests to Prof Hwang:
Surgery, College of Medicine, Hanyang University, Seoul; Private
Department of Dentistry/Oral and Maxillofacial Surgery, College of
Practice, Gimpo, Gyeonggi, Korea.
Medicine, Hanyang University, 222 Wangsimni-ro, Seongdong-gu,
zFormer Chief Resident, Department of Oral and Maxillofacial
133-791, Seoul, Republic of Korea; e-mail: [email protected]
Surgery, Massachusetts General Hospital, Harvard Medical School, Boston; Private Practice, Vienna, VA. xAssociate
Professor,
Department
of
Dentistry/Oral
Received February 16 2015 Accepted May 19 2015 Ó 2015 American Association of Oral and Maxillofacial Surgeons
and
Maxillofacial Surgery, College of Medicine, Hanyang University,
0278-2391/15/00613-8
Seoul, Korea.
http://dx.doi.org/10.1016/j.joms.2015.05.028
kProfessor, Department of Dentistry/Oral and Maxillofacial Surgery, College of Medicine, Hanyang University, Seoul, Korea.
1
2 Mandibular setback is a common surgical procedure to correct dentofacial deformities. Previous studies have shown that retro-positioning of the mandible affects the facial profile and soft tissues, including the pharyngeal airway space.1-3 These studies of bilateral sagittal split ramus osteotomy (BSSO) also have shown posterior-inferior displacement of the hyoid bone and of the tongue in a similar direction.1,2,4,5 Mandibular setback osteotomy can cause narrowing of the pharyngeal airway space that resolves over time, but does not fully recover during followup.2,3,6-8 Cephalograms are standard radiographs used in maxillofacial deformity analysis and orthodontic diagnosis. The lateral cephalogram has been used for its simplicity and economical measurement of the pharyngeal airway.1-4,7,8 However, pharyngeal airway measurements can be affected by the head position at cephalometric analysis. The pharyngeal airway widens anteroposteriorly when the neck is extended and narrows when the neck is flexed. Thus, variations in head posture need to be standardized when comparing data because the results will be unreliable; to obtain accurate and precise measurements of successive changes of the pharyngeal airway, cephalometric analyses should be corrected for craniocervical inclination.9 Several studies have reported that the pharyngeal airway is reduced after mandibular setback surgery.2,3,6-8,10-12 In contrast, Eggensperger et al4 reported the size of pharyngeal airway remains unchanged in the lower portion. In addition, previous studies have reported only short-term changes in the pharyngeal airway after setback surgery1,12 and at longer intervals of 6 months and 1.5 or 2 years postoperatively.2,3,11 Previous studies have not provided specific data on postoperative change patterns of the pharyngeal airway during shorter intervals. There is no consensus on the patterns and tendencies of airway changes after setback surgery. The purpose of this study was to investigate the changes and recovery patterns of the pharyngeal airway during specific postoperative intervals up to 1 year after BSSO for correction of mandibular prognathism. The authors hypothesized that an immediate reduction in airway space postoperatively would recover slowly in proportion to the predictor variable (time) with an incomplete recovery to its original dimension. The specific aims of this study were to measure the pharyngeal airway corrected for head position variations on lateral cephalograms immediately after and at 1, 3, 6, and 12 months after mandibular setback surgery at 3 levels and to compare the pharyngeal airway at each postoperative interval.
PHARYNGEAL AIRWAY RECOVERY AFTER BSSO SETBACK
Materials and Methods STUDY DESIGN
To address the study purpose, the authors designed and implemented a retrospective cohort study and it was granted an exemption in writing by the institutional review board of Hanyang University (Seoul, Korea). The study population was composed of all patients who presented for evaluation and management of dentofacial deformities at the Department of Oral and Maxillofacial Surgery, Hanyang University Hospital from January 1, 2005 through December 31, 2012. To investigate patterns of change of the pharyngeal airway after mandibular setback, this study included only patients who underwent BSSO with a diagnosis of mandibular prognathism and had a normal anteroposterior position of the maxilla at cephalometric measurements and clinical examination. Patients were excluded if they were undergoing combined procedures (Le Fort I osteotomy and genioplasty), had facial asymmetry, had mandibular prognathism associated with craniofacial syndrome (acromegaly syndrome), and were older than 40 years. Also excluded were patients who failed to present for regular follow-up visits and postoperative radiographic studies at any of the defined intervals. STUDY VARIABLES
The primary predictor variable of this study was time. Cephalograms of all patients were taken 6 times: preoperatively, immediately postoperatively, and 1, 3, 6, and 12 months postoperatively. The primary outcome variable of this study was the pharyngeal airway measurement at each interval on cephalograms. The secondary outcome was upper airway length (from the end of the hard palate to the superoposterior area of the hyoid bone) at each interval on cephalograms. Other variables, such as age, gender, and mandibular setback amount by BSSO, also were examined. DATA COLLECTION METHODS
Lateral cephalograms were taken using a standardized technique: the tongue was in a relaxed position; the mandible was in centric occlusion; breathing was through the nose in a relaxed tidal fashion after swallowing once; and the breath was held at the end of the expiratory phase. The distance from the anode to the patient’s midsagittal plane was 150 cm and the distance from the midsagittal plane to the film was 15 cm. All lateral cephalometric radiographs were taken (Orthophos/3C, Siemens, Munich, Germany) and traced using cephalometric landmarks. The linear and angular items were measured, and the landmarks used are shown in Figure 1. First, the
3
JEON ET AL
FIGURE 1. Landmarks shown on lateral cephalogram. Cervical line, line connecting the posterior tangent to the second, third, and fourth cervical vertebra; craniocervical inclination, angle between the Na-S and the cervical line; Frankfort line, line connecting the uppermost point of the external auditory canal to the lowermost point of the orbital rim; level of the most inferior-anterior point on the body of the second cervical vertebra, distance from CV2ia to the posterior wall of the pharyngeal airway parallel to the Frankfort line; level of the midanterior point on the body of the third cervical vertebra, distance from CV3ma to the posterior wall of the pharyngeal airway parallel to the Frankfort line; Na-S, line connecting the midpoint of the pituitary fossa to the nasion; UT level, distance from the UT to the posterior wall of the pharyngeal airway parallel to the Frankfort line. CV2ia, the most inferior-anterior point on the body of the second cervical vertebra; CV2ip, the most inferior-posterior point on the body of the second cervical vertebra; CV3ma, the midanterior point on the body of the third cervical vertebra; CV4ip, the most inferiorposterior point on the body of the fourth cervical vertebra; Na, nasion; Or, orbitale; Po, porion; S, sella turcica; UT, uvular tip. Jeon et al. Pharyngeal Airway Recovery After BSSO SETBACK. J Oral Maxillofac Surg 2015.
Frankfort horizontal line that connects the uppermost point of the external auditory canal with the lowermost point of the inferior orbital rim was marked. Second, the pharyngeal airway distance parallel to the Frankfort horizontal line at 3 levels was measured: the uvula tip, the most inferior-anterior point on the body of the second cervical vertebra (low-C II level), and a midanterior point on the body of the third cervical vertebra (mid-C III level). Also, the angle of the craniocervical inclination was measured to compensate for the effect of variable head postures on the pharyngeal airway space, according to a method adopted from Anegawa et al.9
Briefly, the angle was measured using 2 lines: one connecting the midpoint of the pituitary fossa to the nasion and the other connecting the posterior tangent to the second, third, and fourth cervical vertebrae. Third, the actual pharyngeal airway measurements were corrected using 2 equations. The corrected value of the pharyngeal airway space was calculated with an actual measurement + 0.37 (100.9 angle of craniocervical inclination) for men and an actual measurement + 0.33 (103.5 angle of craniocervical inclination) for women.9 Patients who failed to present for follow-up postoperative radiographs were excluded.
4
PHARYNGEAL AIRWAY RECOVERY AFTER BSSO SETBACK
Table 1. PATIENT DEMOGRAPHICS
Demographic
Value
Age (yr) Mean SD Range Gender, n Men Women Setback (mm) Mean SD Range
23.3 5.48 17-39 30 14 16 8.43 3.36 3-18
was 12.80 3.87 mm (mean standard deviation) preoperatively (Table 2). As presented in Tables 2 and 3, the immediate postoperative pharyngeal airway space was significantly reduced to 8.01 3.78 mm (P < .001), or 61% of its preoperative value. The pharyngeal airway space was significantly recovered to 9.49 3.77 mm, or 74% of its preoperative value, by 1 month after surgery (P < .05). Further statistical changes were not noted 3 and 6 months postoperatively. The pharyngeal airway space recovered to 10.68 3.23 mm, or 84% of its preoperative value, after 12 months. PHARYNGEAL AIRWAY SPACE CHANGES AT LOW-C II LEVEL
Abbreviation: SD, standard deviation. Jeon et al. Pharyngeal Airway Recovery After BSSO SETBACK. J Oral Maxillofac Surg 2015.
STATISTICAL ANALYSES
All statistical analyses were performed using SPSS 20 (SPSS, Inc, Chicago, IL). The normality test was performed and then multivariable analysis of variance was used to measure changes of the pharyngeal airway space over time. Statistical significance was established at the 3 levels as P values less than .05, .01, and .001, respectively.
Results A total of 136 patients underwent BSSO from January 1, 2005 through December 31, 2012. Thirty adult patients met the inclusion criteria during the study period. The mean age was 23.4 years (range, 17 to 39 yr) and 14 patients were men and 16 patients were women. The average amount of surgical setback was 8.43 mm (range, 3 to 18 mm; Table 1). PHARYNGEAL AIRWAY SPACE CHANGES AT UVULAR TIP LEVEL
The measurement values corresponding to time are presented in Table 2. The pharyngeal airway space value
The measurement values corresponding to time are presented in Table 2. The pharyngeal airway value was 13.42 4.07 mm preoperatively (Table 2). As presented in Tables 2 and 3, the immediate postoperative pharyngeal airway was significantly reduced to 9.88 4.17 mm (P < .001), or 73% of its preoperative value. The pharyngeal airway space was significantly recovered to 9.93 3.97 mm, or 76% of its preoperative value, by 1 month after surgery (P < .05) and remained constant thereafter. The pharyngeal airway recovered to 10.82 3.50 mm, or 81% of its preoperative value, after 12 months. PHARYNGEAL AIRWAY SPACE CHANGES AT MID-C III LEVEL
The measurement values corresponding to time are presented in Table 2. The pharyngeal airway value was 12.92 3.57 mm preoperatively (Table 2). As presented in Tables 2 and 3, the immediate postoperative pharyngeal airway space was significantly reduced to 9.83 3.95 mm (P < .001), or 77% of its preoperative value. The pharyngeal airway space was recovered to 10.53 3.19 mm after 1 month, or 87% compared with the preoperative pharyngeal airway space
Table 2. SUCCESSIVE CHANGES OF THE PHARYNGEAL AIRWAY SPACE AND UAL AFTER BILATERAL SAGITTAL SPLIT RAMUS OSTEOTOMY
Airway Level Time PreOP (mm) PostOP (mm) M1 (mm) M3 (mm) M6 (mm) M12 (mm)
UT, Mean SD
CV2ia, Mean SD
CV3ma, Mean SD
UAL, Mean SD
12.80 3.87 8.01 3.78 9.49 3.77 9.60 3.94 9.69 4.00 10.68 3.23
13.42 4.07 9.88 4.17 9.93 3.97 9.83 3.76 10.28 4.04 10.82 3.50
12.92 3.57 9.83 3.95 10.53 3.19 10.57 3.64 11.08 2.88 11.48 2.80
64.06 6.17 73.64 7.79 67.10 7.04 65.60 6.94 66.44 5.64 66.72 6.38
Abbreviations: CV2ia, most inferior-anterior point on the body of the second cervical vertebra; CV3ma, midanterior point on the body of the third cervical vertebra; M1, 1 month after surgery M3, 3 months after surgery; M6, 6 months after surgery; M12, 12 months after surgery; PostOP, immediately after surgery; PreOP, before surgery; SD, standard deviation; UAL, upper airway length; UT, uvular tip. Jeon et al. Pharyngeal Airway Recovery After BSSO SETBACK. J Oral Maxillofac Surg 2015.
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JEON ET AL
Table 3. SUCCESSIVE CHANGES OF THE PHARYNGEAL AIRWAY SPACE AFTER BILATERAL SAGITTAL SPLIT RAMUS OSTEOTOMY BY MULTIVARIABLE ANALYSIS OF VARIANCE
T0-T1 T1-T2 T2-T3 T3-T4 T4-T5
UT
CV2ia
CV3ma
.0002z .015* NS NS NS
.0002z .004y NS NS NS
.0002z NS NS NS NS
Abbreviations: CV2ia, most inferior-anterior point on the body of the second cervical vertebra; CV3ma, midanterior point on the body of the third cervical vertebra; NS, not significant; T0-T1, before surgery to shortly after surgery; T1-T2, shortly after to 1 month after surgery; T2-T3, 1 to 3 months after surgery; T3-T4, 3 to 6 months after surgery; T4-T5, 6 to 12 months after surgery; UT, uvular tip. * Significant at P < .05. y Significant at P < .01. z Significant at P < .001. Jeon et al. Pharyngeal Airway Recovery After BSSO SETBACK. J Oral Maxillofac Surg 2015.
measurement, but it was not statistically meaningful. The pharyngeal airway reached 92% of its preoperative value at 12 months after BSSO. UPPER AIRWAY LENGTH CHANGES AT EACH INTERVAL
The measurement values corresponding to time are presented in Table 2. The upper airway length was 64.06 6.17 mm preoperatively (Table 2). As presented in Table 2, the immediate postoperative upper airway length was significantly increased to 73.64 7.79 mm (P < .001). The upper airway length was significantly recovered to 67.10 7.04 mm by 1 month after surgery (P < .001), 65.60 6.94 mm by 3 months after surgery (P < .01), and 66.44 5.84 mm by 6 months after surgery (P < .001). The upper airway length recovered to 66.72 6.38 mm after 12 months (P < .001).
Discussion The purpose of study was to investigate the pharyngeal airway space changes and recovery patterns during specific postoperative intervals up to 1 year after BSSO for mandibular prognathism. The authors hypothesized that an immediate reduction in airway postoperatively would recover slowly in proportion to time. The specific aim of this study was to measure and compare the pharyngeal airway on preoperative lateral cephalograms with postoperative cephalograms immediately and 1, 3, 6, and 12 months after mandibular setback surgery.
The results of this study confirmed the hypothesis that the pharyngeal airway decreased importantly at all 3 levels immediately after BSSO. This reduction in pharyngeal airway showed an appreciable recovery after 1 month. However, a full recovery was not achieved at 12 months postoperatively. These findings concur with previous studies that have reported incomplete recovery of the pharyngeal airway space after BSSO.2-4,7,8,11 The authors observed that the amount of recovery was different at each time point and was not proportional to time. The pharyngeal airway space was quickly recovered at 1 month, followed by a slower recovery rate during the subsequent 11 months. The rapid change of the pharyngeal airway space took place early in the postoperative phase. Thus, close observation of a patient’s airway for any new signs and symptoms of upper airway obstruction is warranted during this early postoperative period. There are controversies on the amount of pharyngeal airway space changes occurring in surgical patients with mandibular prognathism. Enacar et al13 reported that narrowing persisted from 6 months to 1 year during the average evaluation period. Conversely, Athanasiou et al14 found that the pharyngeal airway recovered by physiologic readaptation within 1 year of mandibular setback surgery. Mao et al15 reported that airway width and area increased during follow-up, but did not return to their original values. The present study identified the recovery patterns of the pharyngeal airway to approximately 74 to 87% from baseline at 1 month postoperatively after correction of mandibular prognathism using BSSO. The pharyngeal airway recovered shortly after surgical repositioning of the mandible. Although complete recovery of the pharyngeal airway was not achieved within 1 year, it is suggested that continuous adaptation occurred to 84, 81, and 92% from baseline, respectively. A long-term follow-up study is warranted to investigate the timing and possibility of full recovery. Therefore, potential incomplete recovery of the pharyngeal airway should be considered, and preoperative signs and symptoms of airway obstruction should be assessed while making a surgical treatment plan for patients with mandibular prognathism. The pharynx is anatomically divided into 3 sections: the nasopharynx (the space between the nose and the soft palate), the oropharynx (the space behind the oral cavity), and the hypopharynx (the space behind the inferior line of the epiglottis).16 The oropharynx includes the part below the soft palate and the posterior tongue,16 and this is the region examined in most studies for the relation between mandibular setback and the pharyngeal airway.13 In the present study, the change patterns of the pharyngeal airway at 12 months after BSSO were similar at all 3 levels, presumably because all levels are in the same
6 oropharyngeal airway. This concurs with the outcome of computed tomographic (CT) studies, which showed only partial recovery of the pharyngeal airway space by 2 to 3 months after surgery.10,12 The upper airway was most reduced postoperatively according to the present findings.17 Riley and Powell18 reported an important correlation between pharyngeal airway measurements on cephalograms and airway volume calculated on CT scans. After mandibular setback surgery, the tongue was the most affected structure in the oral cavity. The pharyngeal airway can be affected mostly by changes in the positions of the hyoid bone, tongue, and soft palate. Therefore, the oropharynx is the most affected region compared with the nasopharynx and hypopharynx.19 Some studies have reported changes in the position of the hyoid bone and reductions in retrolingual and hypopharyngeal airway dimensions after surgery.4,14 Tselnik and Pogrel2 reported a reduction of the retrolingual airway by 28% in length and 12.8% in volume. Posteroinferior displacement of the hyoid bone after surgery, resulting in movement of the tongue in the same direction, also has been reported; the posteriorly displaced tongue can narrow the retrolingual dimension and decrease the pharyngeal airway space.10 The present finding concurs with previous studies reporting the posteroinferior position change of the hyoid bone after BSSO when comparing upper airway length measurements at preoperative and postoperative intervals.2,10 CT scanning is recommended for evaluating volume changes and has been used in many studies. However, CT scanning has its own limitation of capturing a dynamic airway volume with a static series of radiographic images, and the risks from a large amount of radiation exposure to patients do not justify a periodic CT scan for airway measurements and evaluation. Hence, the present study was based on cephalography, which is simple, inexpensive, and noninvasive and causes less discomfort to patients. In addition, all landmarks can be easily located, including the anteroposterior extension of the pharyngeal airway. Cephalographic analysis is not without limitations because a patient’s head posture and mandibular movement can be affected by swallowing. Therefore, the head position of patients should be standardized because the pharyngeal airway space widens when the neck is extended and narrows when it is flexed. When the neck is extended and the craniocervical inclination is increased by 10 , the pharyngeal airway also increases by 3.7 mm in men and 3.3 mm in women.9 In the present study, a corrected pharyngeal airway value was calculated to compensate for variations in head position. Obstructive sleep apnea (OSA) is caused by recurrent upper airway obstructions during the sleep cycle
PHARYNGEAL AIRWAY RECOVERY AFTER BSSO SETBACK
and manifests as loud snoring, arterial oxygen desaturation, sleep fragmentation, and excessive daytime somnolence.20-22 OSA affects 2 to 4% of the general adult population and might be even more frequent in specific subgroups of patients with hypertension or heart failure.20-22 Studies have suggested craniofacial variations for patients with OSA. Some features described are a decreased cranial base length, mandibular or bimaxillary deficiency, increased lower face height, elongated soft palate, large tongue, and inferior positioning of the hyoid bone.23,24 Anatomic narrowing of the upper airway as a result of alterations in craniofacial morphology have been suggested as the cause of OSA.24,25 The size of the pharyngeal airway has received much attention because snoring and sleep apnea are closely linked to each other.5,26 A reduced pharyngeal airway can be found in various circumstances, including obesity, hypertrophic tonsil, adenoid vegetation, a large tongue, and a small jaw. If the pharyngeal airway space narrows, then resistance to airflow increases and this increases the risk of snoring and OSA.2 There is much evidence for an association between the pharyngeal airway and OSA. Riley and Powell18 showed that a pharyngeal airway smaller than 11 mm and a mandibular planeto-hyoid distance longer than 15.4 mm are indicative of OSA. Partinen et al27 reported that patients with a pharyngeal airway smaller than 5.0 mm (base of tongue level) and a mandibular plane-to-hyoid distance longer than 24.0 mm had the highest respiratory disturbance index. Muto et al28 also found a meaningful correlation between the pharyngeal airway and the position of the maxilla, mandible, and soft palate. Thus, it is believed that any alteration of the facial skeleton that replicates these features can increase airway resistance. In the present study, the pharyngeal airway space was reduced 74 to 87% of its original value immediately after mandibular setback surgery. This change can be important if patients have preexisting undiagnosed OSA symptoms. Mandibular prognathism can be corrected by mandibular setback surgery or mandibular setback in conjunction with maxillary advancement. Maxillomandibular advancement, which enlarges the pharyngeal airway, has proved to be a very effective surgical treatment modality for severe OSA.29,30 In a comparative study, bimaxillary surgery reduced the retropalatal dimension, but the effects were not important after 2 years and had much smaller effects than that of mandibular setback alone.3 Thus, bimaxillary surgery rather than mandibular setback surgery alone is preferable for correcting Class III deformities and preventing narrowing of the pharyngeal airway space, a possible predisposing factor for OSA.12 A large mandibular setback might inhibit biological
JEON ET AL
adaptation and can cause sleep-disordered breathing; thus, simultaneous maxillary advancement to minimize the amount of mandibular setback for patients with large anteroposterior discrepancies should be considered.17 This study was composed of Korean patients who had undergone BSSO alone to set back the mandible for correction of mandibular prognathism. In most Asian countries such as Korea, mandibular setback surgery is performed routinely for correction of mandibular prognathism31 and to improve facial contour esthetics. In this respect, data on pharyngeal airway change patterns after mandibular setback surgery would be beneficial to surgeons who are planning BSSO as a surgical modality. The authors confirmed the gradual recovery of the pharyngeal airway over time after BSSO through this study. However, a limitation of this study was a lack of a systematic preoperative evaluation of airway and OSA symptoms with polysomnography or an evaluation of airway dimension using CT scanning at preand postoperative intervals for comparison. Another limitation of this study was not accounting for the degrees of airway improvement associated with weight loss postoperatively. There are other important factors associated with reduction of the pharyngeal airway, such as the position of the hyoid bone and the soft tissue condition during adaptation. Further studies and evaluations related to these various factors should be conducted. Appreciably reduced pharyngeal airway on radiographs immediately postoperatively mostly recovered within 1 month after BSSO followed by a gradual recovery after 3 months. However, full recovery of the pharyngeal airway was not obtained at 12 months postoperatively. Therefore, an increased risk of postoperative airway narrowing and obstruction should be considered before treatment planning for patients undergoing mandibular setback surgery. Research is necessary to evaluate the correlation of amount of setback and its relevance to OSA symptoms.
References 1. Demetriades N, Chang DJ, Laskarides C, et al: Effects of mandibular retropositioning, with or without maxillary advancement, on the oro-naso-pharyngeal airway and development of sleeprelated breathing disorders. J Oral Maxillofac Surg 68:2431, 2010 2. Tselnik M, Pogrel MA: Assessment of the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg 58:282, 2000 3. Chen F, Terada K, Hanada K, Saito I: Predicting the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg 63:1509, 2005 4. Eggensperger N, Smolka W, Iizuka T: Long-term changes of hyoid bone position and pharyngeal airway size following mandibular setback by sagittal split ramus osteotomy. J Craniomaxillofac Surg 33:111, 2005 5. Lye KW: Effect of orthognathic surgery on the posterior airway space (PAS). Ann Acad Med Singapore 37:677, 2008
7 6. Liukkonen M, Vahatalo K, Peltomaki T, et al: Effect of mandibular setback surgery on the posterior airway size. Int J Adult Orthodon Orthognath Surg 17:41, 2002 7. Hochban W, Schurmann R, Brandenburg U, et al: Mandibular setback for surgical correction of mandibular hyperplasia— Does it provoke sleep-related breathing disorders? Int J Oral Maxillofac Surg 25:333, 1996 8. Muto T, Yamazaki A, Takeda S, et al: Accuracy of predicting the pharyngeal airway space on the cephalogram after mandibular setback surgery. J Oral Maxillofac Surg 66:1099, 2008 9. Anegawa E, Tsuyama H, Kusukawa J: Lateral cephalometric analysis of the pharyngeal airway space affected by head posture. Int J Oral Maxillofac Surg 37:805, 2008 10. Kawamata A, Fujishita M, Ariji Y, et al: Three-dimensional computed tomographic evaluation of morphologic airway changes after mandibular setback osteotomy for prognathism. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 89:278, 2000 11. Kim JS, Kim JK, Hong SC, et al: Pharyngeal airway changes after sagittal split ramus osteotomy of the mandible: A comparison between genders. J Oral Maxillofac Surg 68:1802, 2010 12. Degerliyurt K, Ueki K, Hashiba Y, et al: 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 105:495, 2008 13. Enacar A, Aksoy AU, Sencift Y, et al: Changes in hypopharyngeal airway space and in tongue and hyoid bone positions following the surgical correction of mandibular prognathism. Int J Adult Orthodon Orthognath Surg 9:285, 1994 14. Athanasiou AE, Toutountzakis N, Mavreas D, et al: Alterations of hyoid bone position and pharyngeal depth and their relationship after surgical correction of mandibular prognathism. Am J Orthod Dentofacial Orthop 100:259, 1991 15. Mao C, Aruga S, Matsuura M, et al: Changes in airway space following mandibular setback using sagittal split osteotomy and rigid internal fixation. Chin Med Sci J 12:96, 1997 16. Swartz MH: The oral cavity and pharynx, in Swartz MH (ed): Textbook of Physical diagnosis (ed 7). Philadelphia, PA, Saunders Elsevier, 2014, p 278 17. Hasebe D, Kobayashi T, Hasegawa M, et al: Changes in oropharyngeal airway and respiratory function during sleep after orthognathic surgery in patients with mandibular prognathism. Int J Oral Maxillofac Surg 40:584, 2011 18. Riley RW, Powell NB: Maxillofacial surgery and obstructive sleep apnea syndrome. Otolaryngol Clin North Am 23:809, 1990 19. Kim NR, Kim YI, Park SB, et al: Three dimensional cone-beam CT study of upper airway change after mandibular setback surgery for skeletal Class III malocclusion patients. Korean J Orthod 40: 145, 2010 20. Young T, Palta M, Dempsey J, et al: The occurrence of sleepdisordered breathing among middle-aged adults. N Engl J Med 328:1230, 1993 21. Leung RS, Bradley TD: Sleep apnea and cardiovascular disease. Am J Respir Crit Care Med 164:2147, 2001 22. Naughton MT: Sleep disorders in patients with congestive heart failure. Curr Opin Pulm Med 9:453, 2003 23. Bacon WH, Turlot JC, Krieger J, et al: Cephalometric evaluation of pharyngeal obstructive factors in patients with sleep apneas syndrome. Angle Orthod 60:115, 1990 24. Battagel JM, L’Estrange PR: The cephalometric morphology of patients with obstructive sleep apnoea (OSA). Eur J Orthod 18:557, 1996 25. Shelton KE, Woodson H, Gay S, et al: Pharyngeal fat in obstructive sleep apnea. Am Rev Respir Dis 148:462, 1993 26. Ikeda K, Ogura M, Oshima T, et al: Quantitative assessment of the pharyngeal airway by dynamic magnetic resonance imaging in obstructive sleep apnea syndrome. Ann Otol Rhinol Laryngol 110:183, 2001 27. Partinen M, Guilleminault C, Quera-Salva MA, et al: Obstructive sleep apnea and cephalometric roentgenograms. The role of anatomic upper airway abnormalities in the definition of abnormal breathing during sleep. Chest 93:1199, 1988 28. Muto T, Yamazaki A, Takeda S, et al: Relationship between the pharyngeal airway space and craniofacial morphology, taking
8 into account head posture. Int J Oral Maxillofac Surg 35:132, 2006 29. Fairburn SC, Waite PD, Vilos G, et al: Three-dimensional changes in upper airways of patients with obstructive sleep apnea following maxillomandibular advancement. J Oral Maxillofac Surg 65:6, 2007
PHARYNGEAL AIRWAY RECOVERY AFTER BSSO SETBACK 30. Prinsell JR: Maxillomandibular advancement surgery for obstructive sleep apnea syndrome. J Am Dent Assoc 133:1489, 2002 31. Chang-Hwan L, Sang-Han L, Hyun-Soo K, et al: Analysis of familial tendency in skeletal Class III malocclusion. J Korean Assoc Oral Maxillofac Surg 32:506, 2006
