Craniofacial morphology and head posture in Chinese subjects with obstructive sleep apnea

Craniofacial Morphology and Head Posture in Chinese Subjects With Obstructive Sleep Apnea Poh Kang Ang, Andrew Sandham, and Wan Cheng Tan This study measured craniofacial and head posture variables from standardized lateral cephalometric radiographs in Chinese subjects with obstructive sleep apnea (OSA) referred to a university hospital. The investigation was performed in the Sleep Laboratory of the Department of Respiratory Medicine, National University of Singapore. The sample consisted of 61 Chinese male subjects, 25 with mild and 36 with moderate-to-severe OSA diagnosed using overnight polysomnographic studies. Standardized head posture lateral cephalometric radiographs were used to record linear and angular dimensions for head posture and morphology. The moderate-to-severe sample was compared with the mild group, as for ethical reasons no control group with standardized cephalometric radiographs was available. Significant differences were found between hyoid positions for the mild and moderate-to-severe samples with OPA. The hyoid was more caudally placed in the moderate-to-severe sample when measured to the mandibular border (ML; P < 0.05) and to the maxillary plane (NL; P < 0.01). No significant differences were found for other craniofacial variables measured, but the anterior cranial base was shorter, cranial base angle smaller, and gonial angle greater in the moderate-to-severe sample, but this did not reach a level of significance. There were also no significant differences between the values recorded for head posture variables, so the data for the mild and moderate-to-severe samples were pooled and compared with existing published control studies for both Chinese and white subjects. This revealed a marked increase in craniocervical angulation (P < 0.001) for the total OSA study sample for craniovertical (NSL/VER), craniocervical (NSL/OPT), and craniohorizontal (OPT/HOR) variables when compared with each of the various control groups. The study provides evidence that a more caudal hyoid bone position and greater craniocervical angulation are found in subjects with OSA. (Semin Orthod 2004;10:90-96.) © 2004 Elsevier Inc. All rights reserved.

bstructive sleep apnea (OSA) is a potentially life-threatening condition in which the patient suffers periodic cessation of breathing during sleep, which impairs the quality of life. The main presentation is loud snoring of which the individual is usually not aware, and the irregular breathing patterns and restless movements in bed characterize this disorder. OSA is reported to affect 10% of white adults.1,2 There is, however, no information on the prevalence and severity of OSA for South East Asian Chinese, and this may be largely due to the lack of awareness and limited facilities for investigating this problem in these developing regions.

O

From the National Dental Centre Singapore, Singapore; Faculty of Medicine, Academic Hospital (AZG) Groningen, The Netherlands; Faculty of Medicine, National University of Singapore, Singapore. The study was carried out at the Graduate School of Dental Studies, Faculty of Dentistry, and Department of Respiratory Medicine, Faculty of Medicine, National University of Singapore, and was supported by Grant NUS R-172-000-083-213. Address correspondence to Dr Andrew Sandham, Academic Hospital (AZG), Department of Orthodontics, Hanzeplein 1, Postbox 30 001, 9700 RB Groningen, The Netherlands. © 2004 Elsevier Inc. All rights reserved. 1073-8746/04/1001-0009$30.00/0 doi:10.1053/j.sodo.2003.10.008

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Seminars in Orthodontics, Vol 10, No 1 (March), 2004: pp 90-96

Craniofacial Morphology and Head Posture in OSA

Many cephalometric studies3-17 have reported craniofacial and upper airway morphology differences in subjects with OSA when compared with a reference sample, but little information has been presented concerning craniocervical posture. In general, these studies revealed differences between subjects with OSA, when compared with controls, that included maxillary and mandibular retrognathism, steep occlusal plane, increased mandibular plane angle, shorter mandibular length, increased upper and lower facial height, a more caudally positioned hyoid bone, reduced pharyngeal dimensions, overerupted maxillary and mandibular dentition, longer tongue, and changes in pharyngeal spatial position. A few studies have reported the effects of OSA on craniocervical posture in whites when compared with controls.18-21 These studies, in general, showed increased craniocervical angles (NSL/OPT and NSL/CVT) in the OSA sample when compared with the reference group. There are very few studies and very little information on craniofacial morphological variations in Asian Chinese with OSA, and information on craniocervical posture variations is limited.22,23 A few case report studies of OSA in South East Asia have been performed,24-26 but detailed cephalometric investigations have not been reported. The aim of the present study was to measure cephalometric, hyoid, and head posture linear and angular variables for a moderate-to-severe OSA sample for comparison to a mild OSA reference group. Control data were not available for the present study because of ethical concerns, so the pooled OSA craniocervical data were compared with 2 earlier studies on Chinese subjects, 1 performed in Hong Kong22 and the other in Singapore.23 Control data from existing studies of whites were also used for interethnic comparisons.

Subjects and Method The subjects in the present study consisted of 61 Asian Chinese male patients attending the Department of Respiratory Medicine Sleep Laboratory at National University Hospital, Singapore, for investigation of OSA. The mild OSA group consisted of 25 subjects with a mean age of 40.8

91

years and a mean body mass index (BMI) of 28.2 kg/m2, and the moderate-to-severe sample consisted of 36 subjects with a mean age of 44.9 years and a BMI of 28.4 kg/m2. OSA was diagnosed using overnight polysomnographic studies. The subjects were diagnosed with mild or moderate-to-severe OSA based on the respiratory distress index (RDI), which records the number of episodes of apnea (total cessation of airflow for 10 seconds or more) and hypoapnea during the polysomnographic recordings. A consultant respiratory physician specializing in OSA (W.C.T.) carried this out. No subjects with craniofacial anomalies or previous internasal or pharyngeal surgical procedures were included in the study. Lateral cephalometric radiographs were produced following the established procedure for standardized head posture.27 Cephalometric anthropometric landmarks were identified and marked on cellulose acetate tracing paper and the coordinate data for each point were recorded to a data file by a digitizer.* The results from cephalometric studies of craniocervical posture in 2 Chinese and 3 white investigations were used as controls. 1. Sample H & C (Huggare and Cooke22): Hong Kong Chinese. Sample size, 36; mean age, 12 years. 2. Sample Aw (Aw23): Singaporean Chinese. Sample size, 23; mean age, 18.2 years. 3. Sample S & T (Solow and Tallgren28): Danish male dental students. Sample size, 120; age range, 20 to 30 years. 4. Sample H (Huggare29): Finnish male dental students. Sample size, 50; age range, 19 to 30 years. 5. Sample F & S (Fjellvang and Solow30): Danish blind subjects. Sample size, 30; age range, 15 to 35 years.

Craniofacial Measurements The landmarks identified on the cephalometric radiograph defined cranial base angle (n-s-ba) and anterior cranial base length (s-n), mandibular gonial angle (ML/RL), and lower face height (NL/ML) together with sagittal jaw rela-

*Calcomp Drawing Board III 34240, Calcomp Incorporated, Anaheim, CA.

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tionships (s-n-ss, s-n-sm, and ss-n-sm), and hyoid position (hy-ML, hy-NL) (Fig 1). A comprehensive analysis of craniocervical posture was performed using craniocervical (NSL/OPT,NSL/CVT),craniohorizontal(OPT/ HOR, CVT/HOR), and craniovertical angles (NSL/VER, NL/VER). The difference between the 2 postural angles (NSL/OPT and NSL/ CVT) that defined cervical curvature (OPT/ CVT) was also calculated (Fig 2).

Method Error To ensure consistent magnification and to minimize head posture recording errors, the same operator using the same x-ray machine exposed all the standardized lateral cephalometric radiographs for the subjects in the study. Cephalometric radiographs for the control group of Singapore Chinese23 used for comparison were also

Figure 2. Angular measurements for head posture. Craniovertical NSL/VER, NL/VER, and ML/VER; craniocervical NSL/OPT, CVT/OPT; craniohorizontal OPT/HOR, CVT/HOR. Cervical curvature is defined as the angular difference between NSL/OPT and NSL/CVT.

obtained from the same machine with the same operator. The technique for recording standardized head posture has been previously reported27-31 and showed method errors for head posture (NSL/OPT) ranged from 1.5° to 2.6°. The present investigation followed the same guidelines, and duplicate determinations showed no systematic error and no significant differences between the mean values recorded for head posture. Duplicate determinations were also performed for all the linear and angular variables measured on the lateral cephalometric radiograph. The measurements were done 2 weeks apart. A paired t test was performed, and no significant differences were found for any of the craniofacial and airway variables in the 2 data sets.

Statistics Figure 1. Cephalometric points that define linear and angular variables for cranial base angle (n-s-ba), anterior cranial base length (s-n), mandibular gonial angle (ML/RL), lower face height (NL/ML), sagittal jaw relationships (s-n-ss, s-n-sm, ss-n-sm), and hyoid bone position (hy-ML, hy-NL). Craniocervical posture (OPT/NSL) is defined using points n and s, together with a tangent to the odontoid process (cv2tg and cv2IP).

The recorded data were processed using statistical procedures performed using SPSS 11.0 for Windows®. Student’s t test was used to compare the means for the 2 data sets. The distribution form was analyzed using tests for skewness and kurtosis. This ensured that similar distribution forms were compared and also served to “debug” the data by identifying outliers in the dis-

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Craniofacial Morphology and Head Posture in OSA

Table 1. Statistical Comparison of Mean Values for Cephalometric and Hyoid Variables in Chinese Subjects Diagnosed With Mild and Moderate-to-Severe Obstructive Sleep Apnea (OSA) Mild OSA (n ⫽ 25)

Moderate Severe OSA (n ⫽ 36)

Cephalometric and Hyoid Variables

Mean

SD

Mean

SD

P Value

s-n (mm), anterior cranial base n-s-ba (°), cranial base angle NL/ML (°), vertical jaw relation ML/RL (°), gonial angle s-n-ss (°), maxillary position s-n-sm (°), mandibular position ss-n-sm (°), interjaw relation hy-ML (mm), hyoid to mandible hy-NL (mm), hyoid to maxilla

72.00 128.06 25.40 123.68 82.79 79.99 3.66 20.70 77.17

3.08 4.73 7.83 9.03 3.09 3.83 2.20 6.02 6.04

71.19 126.05 25.69 124.62 83.44 79.67 4.27 24.70 82.74

3.50 5.19 6.96 9.58 3.73 4.39 2.10 7.00 6.67

0.352 0.129 0.879 0.701 0.477 0.772 0.280 0.024* 0.002†

*P ⬍ 0.05; †P ⬍ 0.01.

tribution form that may have occurred due to incorrect sequencing during digitization.

Results Cephalometric Variables The statistical comparison of cephalometric variables between the mild and moderate-to-severe OSA samples showed mean values for anterior cranial base length (s-n) and cranial base angle (n-s-ba) to be smaller in the moderate-to-severe sample when compared with the mild group; and the lower jaw, however, tended to be more retrognathic (P ⫽ 0.28), but none of these differences were significant (Fig 1 and Table 1). A more caudally placed hyoid bone was however found in the moderate-to-severe OSA sample when compared with the mild OSA group (hy-ML, P ⬍ 0.05; hy-NL, P ⬍ 0.01) (Fig 1 and Table 1).

Craniocervical Variables Values for head posture were scrutinized and no significant differences were seen for craniocervical (NSL/OPT, NSL/CVT), craniohorizontal (OPT/HOR, CVT/HOR), and craniovertical (NSL/VER, NL/VER) measurements when mean values for mild OSA and moderate-to-severe OSA subjects were compared. These values were therefore pooled and compared with existing controls. The mean values for craniovertical posture in OSA were 100.0° (NSL/VER) and 93.9° (NL/VER), for craniocervical posture 107.1° (NSL/OPT) and 98.2° (NL/OPT), and for craniohorizontal posture 97.9° (OPT/HOR) and 100.6° (CVT/HOR) (Table 2).

When pooled values recorded for craniocervical posture (NSL/VER, NSL/OPT, OPT/ HOR) were compared with existing control data studies22,23,28-30 (Table 3) for both Chinese and white subjects, all the postural angles for the OSA sample were markedly increased (P ⬍ 0.001; Table 3). Only in the study by Huggare,29 of Finnish dental students, did the level of significance vary for the value of craniocervical posture (NSL/VER; P ⬍ 0.05). No values for craniohorizontal posture (OPT/HOR) were available in the Singapore study.23 In general, craniocervical posture seems to differ between the racial groups in the control samples with higher postural angles found in Chinese.

Discussion The investigation showed very few differences in craniofacial morphology between the mild and moderate-to-severe samples. This is somewhat surprising since previous studies have found differences in both morphology4-19 and head posTable 2. Craniocervical Postural Variables in the Total Obstructive Sleep Apnea OSA Sample N ⫽ 61 Craniovertical NSL/VER NL/VER Craniocervical NSL/OPT NL/OPT Craniohorizontal OPT/HOR CVT/HOR Cervical curvature OPT/CVT

Min (°)

Max (°)

Mean (°)

SD

90.03 90.06

112.26 102.10

99.95 93.86

4.69 2.99

90.52 90.21

122.93 112.76

107.13 98.24

6.98 6.00

90.28 90.23

109.68 115.12

97.87 100.55

4.89 4.59

0.05

9.08

3.26

2.11

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Table 3. Craniovertical, Craniocervical, and Craniohorizontal Pooled Data for the Obstructive Sleep Apnea (OSA) Sample Compared to Control Studies NSL/VER Craniovertical Study Samples OSA sample N ⫽ 61 Control groups Chinese 1. N ⫽ 36 2. N ⫽ 23 White 3. N ⫽ 120 4. N ⫽ 50 5. N ⫽ 30

Mean 100.0

SD 4.7

NSL/OPT Craniocervical Mean 107.1

OPT/HOR Craniohorizontal

SD

Mean

SD

7.0

97.9

4.9

H&C Aw

1994 1998

97.0† 95.9†

6.2 4.2

97.0† 99.2†

6.8 5.1

91.3† —

6.8 —

S&T Huggare F&S

1971 1986 1986

92.6† 96.9* 85.2†

4.7 5.2 8.8

90.4† 95.7† 83.6†

5.9 7.6 10.0

92.2† 91.9† 91.6†

6.0 6.9 6.4

Chinese: 1 ⫽ Huggare and Cooke (1994); 2 ⫽ Aw (1998). White: 3 ⫽ Solow and Tallgren (1971); 4 ⫽ Huggare (1986); 5 ⫽ Fjellvang and Solow (1986) (blind subjects). *P ⬍ 0.05; †P ⬍ 0.001.

ture in subjects with OSA.20-23 Previous investigators, however, have compared samples with more severe sleep apnea to a control group of unaffected subjects, and this may partially explain these findings. The more caudal position of hyoid bone is a frequent finding in previous studies, however, and is confirmed in the present investigation. This study was performed on Chinese patients with moderate-to-severe OSA for comparison to a mild OSA group The results seem to suggest that craniofacial morphology in Chinese subjects does not markedly differ as severity of OSA increases, although anterior cranial base (s-n) and cranial base angle (n-s-ba) are smaller, and although a more retrognathic lower jaw (s-n-sm) is found in the moderate-to-severe sample, these differences are not significant when compared with the mild OSA reference group. These smaller dimensions, however, could contribute to reduction of airway patency, and should perhaps be investigated further by using a sample of patients with more severe OSA. What also may explain the findings is that, within the total sample selected, there may be insufficient difference in severity of sleep apnea between the groups to reveal any marked differences both for craniofacial and head posture values. In a study of head posture in patients with OSA, Solow and coworkers19 assembled OSA data for head posture for 50 male subjects. The mean value recorded for craniovertical posture was 95.1° (NSL/VER), for craniocervical posture

104.1° (NSL/OPT), and for craniohorizontal posture 81.0° (OPT/HOR). There were similar ethical problems in that investigation with assembling normative head posture data from lateral cephalometric radiographs for comparison, so the mean values derived from OSA patients were compared with 6 previous normative studies. The present study follows this approach and uses control data from 2 previous studies on Chinese subjects, and 3 previous studies on white subjects, to observe interethnic differences (Table 3). One of the white cohorts was congenitally blind. The Singaporean Chinese control group23 was assembled in the same center, however, and the radiographs taken by the same operator as for the present investigation, which enhances its value as a reference group. For the postural variables used for comparison in the pooled OSA sample (NSL/VER, NSL/OPT, OPT/HOR), the values recorded were, in general, markedly higher than for both the Chinese and white control groups (Table 3). There also appear to be racial differences between the normative data for Chinese and whites, with Chinese craniocervical postural angles being somewhat greater than that for whites. Indeed, Cooke and Wei32 found intersex and racial differences in a previous study and this could form the basis for further investigation. Craniocervical angulation (NSL/OPT) is representative of both head posture and forward inclination changes of the cervical column, which explains the large differences (10.1°)

Craniofacial Morphology and Head Posture in OSA

found for NSL/OPT in the pooled sample when compared with the Chinese controls. Differences in craniovertical angulation are generally smaller, as head posture changes alone contribute to the difference, and this is confirmed by the study. The blind cohort (F & S30) is interesting because it confirms that a reproducible postural position of the head exists without visual reference, but the craniovertical angle is much lower than the other studies, which indicates the head is generally held lower. The craniocervical angle may be useful as a diagnostic or monitoring measurement in subjects with OSA, because it represents both head posture and cervical vertebral compensatory changes. Extreme extension of both the head and cervical column, however, may represent an overactive compensatory mechanism that ultimately leads not to reduction of airway resistance, but rather has an adverse effect on airway patency that further compounds the obstructive problem. The present study does confirm that there is a change in hyoid bone position and a marked head posture adaptation in Chinese subjects with OSA, and that a racial difference may exist for craniocervical posture between Chinese and white controls.

References 1. Riley R, Guilleminault C, Herran J, Powell N. Cephalometric analyses and flow-volume loops in obstructive sleep apnoea patients. Sleep 1983;6:303-311. 2. Sher AE, Thorpy MJ, Shprintzen RJ, et al. Predictive value of Muller Maneuver in selection of patients for uvulopalatopharyngoplasty. Laryngoscope 1985;9:14831487. 3. Rivlin J, Hoffstein V, Kalbfleisch J, McNicholas W, et al. Upper airway morphology in patients with idiopathic obstructive sleep apnea. Am Rev Respir Dis 1984;129: 355-360. 4. Lowe AA, Santamaria JD, Fleetham JA, et al. Facial morphology and obstructive sleep apnoea. Am J Orthod Dentofacial Orthop 1986;90:484-491. 5. DeBerry-Borowiecki B, Kukwa A, Blanks RH. Cephalometric analysis for diagnosis and treatment of obstructive sleep apnoea. Laryngoscope 1988;98:226-234. 6. Bacon WH, Turbot JC, Krieger J, et al. Craniofacial characteristics in patients with obstructive sleep apnoeas syndrome. Cleft Palate J 1988;25:374-378. 7. Bacon WH, Turbot JC, Krieger J, et al. Cephalometric evaluation of pharyngeal obstructive factors in patients with sleep apnoeas syndrome. Angle Orthod 1990;60: 115-122. 8. Lyberg T, Krogstad Djupesland G. Cephalometric anal-

9.

10.

11.

12.

13.

14.

15.

16.

17.

18. 19. 20.

21.

22.

23.

24.

25.

26.

95

ysis in patients with obstructive sleep apnoea syndrome. J Laryngol Otol 1989;103:293-297. Zucconi M, Ferini-Strambi L, Palazzi S, et al. Habitual snoring with and without obstructive sleep apnoea: the importance of cephalometric variables. Thorax 1992;47: 157-161. Maltais F, Carrier G, Cormier Y, et al. Cephalometric measurements in snorers, non-snorers, and patients with sleep apnoea. Thorax 1991;46:419-423. Andersson L, Brattstron V. Cephalometric analysis of permanently snoring patients with and without obstructive sleep apnea syndrome. Int J Oral Maxillofac Surg 1991;20:159-162. Pracharktam N, Hans MG, Strohl KP, et al. Upright and supine cephalometric evaluation of obstructive sleep apnoea syndrome and snoring subjects. Angle Orthod 1994;64:63-72. Pae EK, Lowe AA, Sasaki K. Cephalometric and electromyographic study of upper airway structures in the upright and supine positions. Am J Orthod Dentofacial Orthop 1994;106:52-59. Lowe AA, Fleetham JA, Adachi S, et al. Cephalometric and computed tomographic predictors of obstructive sleep apnoea severity. Am J Orthod Dentofacial Orthop 1995;107:589-595. Frohberg U, Naples RJ, Jones DL. Cephalometric comparison of characteristics in chronically snoring patients with and without sleep apnoea syndrome. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;80:28-33. Pracharktam N, Nelson S, Hans M. Cephalometric assessment in obstructive sleep apnoea syndrome. Am J Orthod Dentofacial Orthop 1996;109:410-419. Battagel JM, L’Estrange PR. The cephalometric morphology of patients with obstructive sleep apnoea. Eur J Orthod 1996;18:557-569. Solow B, Ovesen J, Neilsen PW, et al. Head posture in obstructive sleep apnoea. Eur J Orthod 1993;15:107-114. Solow B, Skov S, Ovesen J, et al. Airway dimensions in obstructive sleep apnoea. Eur J Orthod 1996;18:571-579. Tangugsorn V, Skatvedt O, Krogstad O, Obstructive sleep apnoea: A cephalometric study. Part I: Cervicocraniofacial skeletal morphology. Part II: Uvulo-glossopharyngeal morphology. Eur J Orthod 1995;17:46-67 Ozbek MM, Miyamoto K, Lowe AA, et al. Natural head posture, upper airway morphology and obstructive sleep apnoea severity in adults. Eur J Orthod 1988;20:133-143. Huggare JAV, Cooke MS. Head posture and cerviovertebral anatomy as mandibular growth predictors. Eur J Orthod 1994;16:175-180. Aw A. Dimensional changes in the upper airway following surgery to correct mandibular prognathism. MDS thesis, National University of Singapore, 1998. Lim TK, Tan WC. The obstructive sleep apnoea syndrome: Case studies. Ann Acad Med Singapore 1985;14: 435-438. Chiu HFK, Lee S, Ho KW, et al. Sleep apnoea syndrome—A study of 5 cases. Singapore Med J 1990;31: 466-468. Tan WC, Koh TH. Evaluation of obstructive sleep apnoea in Singapore using computerised polygraphic monitoring. Ann Acad Med Singapore 1991;20:196-200.

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27. Solow B, Tallgren A. Head posture and craniofacial morphology. Am J Phys Anthropol 1976;44:417-436. 28. Solow B, Tallgren A. Natural head posture in standing subjects. Acta Odont Scand 1971;29:591-607. 29. Huggare J. Head posture and craniofacial morphology in adults from northern Finland. Proc Finn Dent Soc 1986;82:199-208. 30. Fjellvang H, Solow B. Craniocervical postural relations

and craniofacial morphology in 30 blind subjects. Am J Orthod 1986;90:327-334. 31. Solow B, Sierbæk-Nielsen S, Greve E. Airway adequacy, head posture, and craniofacial morphology. Am J Orthod 1988;86:214-223. 32. Cooke MS, Wei SHY. Intersex differences in craniocervical morphology and posture in Southern Chinese and British white persons. Am J Phys Anthrop 1988;77:43-51.