Long-term changes of hyoid bone position and pharyngeal airway size following mandibular setback by sagittal split ramus osteotomy

ARTICLE IN PRESS Journal of Cranio-Maxillofacial Surgery (2005) 33, 111–117 r 2004 European Association for Cranio-Maxillofacial Surgery doi:10.1016/j.jcms.2004.10.004, available online at http://www.sciencedirect.com

Long-term changes of hyoid bone position and pharyngeal airway size following mandibular setback by sagittal split ramus osteotomy Nicole EGGENSPERGER, Wenko SMOLKA, Tateyuki IIZUKA Department of Cranio-Maxillofacial Surgery (Head: Prof. Dr. Dr. J. Raveh), University of Berne, Switzerland Available online 28 January 2005

SUMMARY. Introduction: The purpose of this study was to determine long-term changes in hyoid bone position and pharyngeal airway size after mandibular setback osteotomies. Material and methods: Serial cephalograms of 12 patients who underwent mandibular setback surgery were evaluated preoperatively, at 1 week, 6 months, and 14 months postoperatively, and finally after an average of 12 years. Results: A mean setback of 5.6 mm was associated with a posterior and inferior movement of the hyoid bone. At long-term follow-up, the hyoid bone adapted horizontally to a position about 1.6 mm more posterior than its preoperative location. Immediately after surgery, the length of suprahyoid muscles correlated significantly with skeletal movements: suprahyoid muscles shortened by 4 mm but started lengthening after 1 year. Thereafter, it tended to correlate with the change of hyoid bone position rather than with skeletal relapse. Following the initial decrease after surgery, the size of the lower pharyngeal airway remained almost unchanged. The upper and middle pharyngeal airway sizes continued to decrease over the postoperative period of 12 years, and ultimately were smaller than their preoperative sizes by about 1.5 and 3 mm, respectively. r 2004 European Association for Cranio-Maxillofacial Surgery

Keywords: Mandibular setback; Hyoid bone; Pharyngeal airway size; Skeletal relapse; Cephalometric analysis; Orthognathic surgery

ture. The possible decreased tension of suprahyoidal musculature may change the balance within the head and neck musculature. This can result in an increased anteriorly directed force caused by the neck muscles, pulling the mandible forward again (Gu et al., 2000). If the oropharyngeal complex exerts such an influence over a prolonged period, the related changes in position of the hyoid bone and in the length of the suprahyoid muscles may contribute to skeletal relapse. Furthermore, the decrease in pharyngeal airway size could induce breathing problems (Riley et al., 1987; Hochban et al., 1996). A number of studies have reported postoperative development of obstructive sleep apnoea syndrome (OSAS) after mandibular setback surgery (Riley et al., 1987; Hochban et al., 1996; Liukkonen et al., 2002; Samman et al., 2002). There are differing opinions about the extent and duration of postoperative changes in hyoid bone position. Some studies have suggested that changes in the oropharyngeal complex caused by mandibular setback may be only a temporary phenomenon observed during a relatively short-term postoperative stage (Athanasiou et al., 1991; Gu et al., 2000; Samman et al., 2002). Enacar et al. (1994) found that the hyoid bone tends to return almost to its original preoperative position postoperatively. However, others (Achilleos et al., 2000; Tselnik and Pogrel, 2000; Gu et al., 2000) stated that the hyoid bone never regains its original position. These studied only

INTRODUCTION Mandibular setback using bilateral sagittal split osteotomy (BSSO) is routinely used as an orthognathic surgical procedure to treat mandibular prognathism. The oropharyngeal complex is also affected by a posterior movement of the mandible. Previous studies have shown changes in position of the tongue and the hyoid bone and in the size of the pharyngeal airway which follow mandibular setback (Riley et al., 1987; Athanasiou et al., 1991; Enacar et al., 1994; Hochban et al., 1996; Achilleos et al., 2000; Gu et al., 2000; Kawamata et al., 2000; Tselnik and Pogrel, 2000; Liukkonen et al., 2002; Samman et al., 2002). Changes in tongue position can be analyzed more precisely by measuring changes in hyoid bone position. Postero-inferior displacement of the hyoid bone has generally been noted postoperatively, carrying the tongue backward and downward (Athanasiou et al., 1991; Enacar et al., 1994; Gu et al., 2000; Kawamata et al., 2000). This positional change of the tongue has been shown to decrease the pharyngeal airway size (Enacar et al., 1994; Achilleos et al., 2000; Kawamata et al., 2000; Tselnik and Pogrel, 2000; Liukkonen et al., 2002). Postoperative changes in the pharyngeal complex may influence clinical features such as skeletal relapse and the airway size. It has been postulated that the postoperative alteration in position of the hyoid bone may cause relaxation of the suprahyoidal muscula111

ARTICLE IN PRESS 112 Journal of Cranio-Maxillofacial Surgery

changes in hyoid bone position and pharyngeal airway size between 1 and 3 years postoperatively (Athanasiou et al., 1991; Enacar et al., 1994; Achilleos et al., 2000; Gu et al., 2000; Kawamata et al., 2000; Tselnik and Pogrel, 2000). To our knowledge, the longest follow-up reported in the literature was 3 years (Achilleos et al., 2000; Gu et al., 2000). In fact, the long-term stability of the oropharyngeal complex after mandibular setback is unknown. The purpose of this study was to cephalometrically determine long-term changes in hyoid bone position and pharyngeal airway size 12 years (on average) after mandibular setback in single-jaw surgery. The relationship between the length of suprahyoid musculature and long-term skeletal relapse was also analyzed. MATERIAL AND METHODS Thirty-two consecutive patients had combined orthodontic and surgical treatment of skeletal class III malocclusion between 1986 and 1989 at the Department of Cranio-Maxillofacial Surgery, University of Berne, Switzerland. Of these patients, 12 (38%) were available for a long-term cephalography in 2002. The mean time between the primary orthognathic surgery and the final cephalometric examination was 12 years (range 11–14 years). There were three women and nine men with a mean age of 28 years (range 18–54 years) at surgery, and 41 years (range 29–68 years) at the latest follow-up. The patients were surgically treated by BSSO and mandibular setback (without genioplasty) according to the Obwegeser-Dal Pont method. The bone fragments were fixed using three positioning screws (2 mm diameter) at each osteotomy site. No splints were used for stabilization of the mandible during surgery. Rigid intermaxillary fixation was maintained for 4–6 days postoperatively, followed by functional training with light-guiding elastics. All patients had pre- and postoperative orthodontic treatment. The mean duration of postoperative orthodontic treatment was 14 months (range 11–20 months). In all cases, cephalometric radiographs were taken 1–2 days prior to the operation (T0), 1 week (T1) and 6 months (T2) after surgery, after completion of postoperative orthodontic treatment at 14 months on average (T3), and after long-term follow-up of 12 years (T4). Magnification for linear measurements was 3.3%, which was not corrected. All radiographs were traced and analyzed by the same examiner. As a basis for the measurement, an x–y cranial base coordinate system was constructed on the radiographs. An x-axis was drawn 7 degrees to the Sella-Nasion line (NSL) as a horizontal reference line. A constructed vertical reference line was drawn perpendicular to this line at sella (y-axis) Fig. 1 and Table 1). At the latest examination (T4), an attempt was made to obtain cephalometric radiographs comparable to those taken preoperatively (T0) and during the

Fig. 1 – Hard and soft tissue landmarks used in cephalometric analysis.

first 14 months postoperatively (T1, T2 and T3). To minimize the variability in head position during the radiographic examination, ear rods were used to position the head in the cephalostat. The Sella–Nasion plane was used as a stable reference for recording hyoid bone changes in order to keep measurement error at a minimum. Mandibular movements were determined by measuring positional changes of hard-tissue landmarks such as B-point, pogonion (Pg) and menton (Me), as well as changes in maxillo-mandibular plane angle (ML-NL). Changes of the position of the hyoid bone were determined using the most anterior and superior points of the body of the hyoid bone, as described by Wessberg et al. (1982). The length of the suprahyoid musculature was cephalometrically defined as the distance between menton and the most anterior and superior point of the body of the hyoid bone (H; Fig. 1). The suprahyoid musculature was considered to be relaxed when the distance between menton and the hyoid bone had decreased. To determine a possible correlation between the extent of relaxation of the suprahyoid muscles and skeletal relapse, the cephalometric length of the musculature was compared with positional changes of the skeletal landmarks (B-point and pogonion). The size of the upper pharyngeal airway (Upw–Spp) was defined as the distance between the upper pharyngeal wall (Upw; pharyngeal intersection of a line perpendicular to a line connecting Basion and Sella) and the posterior nasal spine (Spp). The middle pharyngeal airway (Mpw–Spp) was defined as the distance between the middle pharyngeal wall (Mpw; pharyngeal intersection of posterior nasal spine and Basion) and the posterior nasal spine (Spp). The size of the lower pharyngeal airway (Lpw–Spp) was defined as the pharyngeal intersection of a perpendicular line from the tongue body to the pharyngeal wall, touching the most superior point of the epiglottis (E; Fig. 1 Gu et al., 2000; Liukkonen et al., 2002; Samman et al., 2002).

ARTICLE IN PRESS Long-term changes of hyoid bone position and pharyngeal airway size 113 Table 1 – Definitions of skeletal and pharyngeal landmarks used in cephalometric analysis Landmark

Definition

B Pg Me S N Ba Spp E H Upw

B-point: innermost point on concavity of mandible between incisor tooth and bony chin Pogonion: most anterior point on osseus contour of chin Menton: most inferior point of symphysis Sella: centre of sella turcica Nasion: most anterior point of frontonasal suture Basion: most inferior point of clivus Posterior nasal spine: most posterior point of hard palate Epiglottis: most superior point of epiglottis Hyoid bone: most superior and anterior point of hyoid bone Upper pharyngeal width: pharyngeal intersection of a line perpendicular from posterior nasal spine to a line connecting Basion and Sella Middle pharyngeal width: pharyngeal intersection of posterior nasal spine and Basion Lower pharyngeal width: pharyngeal intersection of a perpendicular from the tongue body to pharyngeal wall, touching the most superior point of epiglottis Maxilllo-mandibular plane angle: angle between mandibular plane and maxillary (nasal) plane

Mpw Lpw ML-NL

Table 2 – Postoperative changes (means and standard deviations) of skeletal and pharyngeal airway landmarks n ¼ 12

T0–T1

Horizontal (mm) B 5.6* Pg 5.7* Me 6.3* H 2.5 Vertical (mm) B 3.8 Pg 1.3 Me 0.6 H 7.5* Angular (1) ML-NL 0.9

SD

T1–T2

SD

T2–T3

SD

T3–T4

SD

T1–T4

0.8 1.5 0.8 0.4

3.2 4.9 2.5 6.0

0.1 0.2 1.7 0.9

T0–T4

SD

3.4 4.5 3.3 6.9

5.5* 5.8* 4.6* 1.6

4.5 5.6 4.9 6.3

SD

6.0 7.7 6.9 5.5

0.3 0.3 1.7 1.0

3.0 4.1 3.1 4.2

0.9 1.0 0.8 0.5

4.0 5.0 3.1 6.4

12.0 4.4 2.7 4.3

0.2 0.4 0.2 4.3*

13.6 2.1 1.4 3.3

1.6 0.0 0.2 0.3

7.1 3.0 1.3 2.5

2.2* 1.6 1.6* 0.8

2.5 3.8 1.7 2.5

3.9 2.0* 1.3* 3.3*

11.2 2.7 2.1 3.4

0.2 0.7 0.7 4.3*

4.0 3.9 2.5 2.8

3.1

0.0

2.7

0.4

1.4

1.2

3.4

1.6

4.3

0.7

4.4

Statistical significance was calculated between time intervals T0–T1, T1–T2, T2–T3, T3–T4, T1–T4 and T0–T4 with T0 ¼ Preop., T1 ¼ 1 week, T2 ¼ 6 months, T3 ¼ 14 months and T4 ¼ 12 years postop. * po0.05, SD ¼ standard deviation. ‘–’ indicating movement to left (posterior) or upwards.

Values measured were compared between the six different time intervals T0–T1, T1–T2, T2–T3, T3–T4, T1–T4, and T0–T4. Standard statistical parameters were used to evaluate the linear and angular results. The systematic and accidental errors of the cephalometric analysis has been described elsewhere (Thu¨er et al., 1994). They duplicated determinations of 21 cephalograms and selected at random seven cephalograms. These were retraced and remeasured. No systematic error was found when the values were evaluated with a paired t-test. The accidental errors (si) were calculated with the formula sffiffiffiffiffiffiffiffiffiffiffi P 2 d ; si ¼ 2n where d is the difference between the repeated measurements and n is the number of duplicate determinations. Most of the angular variables and coordinates of the skeletal reference points had accidental errors smaller than 1.01 or 1.0 mm, respectively. Statistical analysis was performed using the Wilcoxon-matched pairs signed-ranks test to determine

the difference between measurements at each interval. Statistical significance was defined as po0.05. Spearman’s rank correlation analysis was used to test the significance of relationships between variables, before and after surgery.

RESULTS Postoperative mandibular movements in the horizontal and vertical planes and mandibular angular changes The initial setback (T0–T1) was on average 5.6 mm at B-point, 5.7 mm at pogonion, and 6.3 mm at menton (means; Table 2). From the early postoperative stage (T1) to 14 months postoperatively (T3), there was further posterior movement of B-point measuring 0.6 mm, whereas pogonion and menton showed skeletal relapse of 1.3 mm and 0.9 mm, respectively. Most skeletal relapse at B-point occurred between 1 and 12 years postoperatively (T3–T4). At the final follow-up (T4), values for B-point and pogonion were the same as those measured at T1. Thus, no further skeletal relapse resulted during 12 years

ARTICLE IN PRESS 114 Journal of Cranio-Maxillofacial Surgery

postoperatively. The net mandibular setback (T0–T4) was 5.5 mm at B-point, 5.8 mm at pogonion, and 4.6 mm at menton (po 0.01, Wilcoxon-matched pairs test). In the vertical plane, the initial (T0–T1) upward movement was 3.8 mm at B-point, 1.3 mm at pogonion, and 0.6 mm at menton (means; Table 2). In the first year after surgery (T1–T3), there was a downward movement of 1.8 mm for B-point and 0.4 mm for pogonion, whereas menton moved upwards 0.4 mm (means). In the following 11 years (T3–T4), B-point and menton moved significantly downwards by 2.2 and 1.6 mm, respectively (po0.05, Wilcoxonmatched pairs test). Postoperative changes of the hyoid bone As an immediate result of the surgery, at T1 there was a 2.5 mm posterior movement of the hyoid bone and a significant 7.5 mm inferior movement (po0.01, Wilcoxon-matched pairs test, Table 2 and Fig. 2). This posterior movement correlated moderately with horizontal surgical changes of B-point (r ¼ 0.5, Spearman) and with those of pogonion and menton (r ¼ 0.8, 0.6, respectively; Spearman; po0.05). In the first 6 months after surgery (T1–T2), the hyoid bone moved 1 mm anteriorly, whereas in the vertical dimension there was a 4.3 mm superior change (po0.001, Wilcoxon-matched pairs test). Up to 14 months postoperatively (T2–T3) there were no further significant changes in either the horizontal or the vertical axis. During this postoperative period (T1–T3), positional changes of the hyoid bone correlated only weakly with those of B-point, pogonion, and menton (ro0.3, Spearman). Twelve years postoperatively (T0–T4), the hyoid bone was

-0.3

-0.7

0.6

1.0

-0.5

0.3

-0.9

1.6 mm posterior and 4.3 mm inferior to its preoperative position. The total change of hyoid bone position also correlated weakly with changes of Bpoint, pogonion, and menton (ro0.2; Spearman). The final positional changes of the skeletal landmarks measured at B-point, pogonion, and menton between T0 and T4 were almost the same at each point (Fig. 3). At the immediate postoperative stage (T1), posterior movement of the hyoid bone was 41% of the amount of mandibular setback. Accordingly, the length of the suprahyoid musculature decreased significantly by 4.0 mm (T0–T1; po0.05, Wilcoxonmatched pairs test). This decrease in length of suprahyoid musculature correlated significantly with surgical (T0–T1) changes of menton (r ¼ 0.6, Spearman; po0.05). In the following 12 months (T1–T3), the length of the suprahyoid musculature increased only from 41.0 mm at T1 to 41.3 mm at T3. Between T3 and T4, the length ‘increased’ by 0.6 mm.Ultimately, from the preoperative (T0) length of 45.0 mm to the length at long-term follow-up (T4) of 41.9 mm, there was a 3.1 mm total decrease in length Postoperative changes of suprahyoid musculature between T1 and T4 correlated significantly with postoperative changes in the position of the hyoid bone (r ¼ 0.7, Spearman; po0.05). Postoperative changes in pharyngeal airway size Initially after mandibular setback (T0–T1), there was a decrease of 0.3 mm (mean) upper and lower pharyngeal airway size (Upw–Spp, Lpw–Spp; Fig. 4). Middle pharyngeal airway size (Mpw–Spp) decreased 1.1 mm (Table 2). Correlations between initial Lpw–Spp and B-point or hyoid bone changes were moderate (r ¼ 0.6 and 0.5, respectively, Spearman;

0.2

(mm)

-2.5 0.4

-5.6

T0

T1

T2

0.8

T3

T4

Time point Lpw-Spp

Hyoid

B-point

Fig. 2 – Horizontal (x-axis) changes of lower pharyngeal airway size (Lpw–Spp), B-point and hyoid bone (H). From preoperatively to early postoperatively (T0–T1), correlations between B-point and hyoid bone as well as between Lpw–Spp and hyoid bone are moderate. There is a significant and strong correlation between the total horizontal changes of Lpw–Spp and B-point from preoperative measurement to longterm follow-up (T0–T4).

ARTICLE IN PRESS Long-term changes of hyoid bone position and pharyngeal airway size 115

Length of suprahyoidal musculature (H – Me)

-5.6

0.3

-5.7

(mm)

-6.3

45.0

- 2.5

-0.8

41.7

1.0

T0

T1

0.8 0.8

1.0

1.7

41.0

-1.5

-0.9

0.3

41.3

-0.5

T2

Pogonion

41.9

0.4

T3 Time point Menton

T4

B-point

Hyoid

Fig. 3 – Horizontal changes of skeletal landmarks and hyoid bone and length of suprahyoidal musculature. Initial lengthening (T0–T1) of the suprahyoid musculature being the distance between menton and hyoid points, correlates significantly with the horizontal initial (x-axis) changes at menton (T0–T1). Total postoperative increase in the length of suprahyoid musculature (T1–T4) correlated significantly with postoperative horizontal changes of the hyoid bone (T1–T4).

Pharyngeal airway size (mm)

24.7 21.7

11.7

T0

-1.1

0.0

-0.1

-0.2

-0.2

-0.7

0.6

-1.8

-0.3

-0.3

T1 Mpw-Spp

T2

-0.8

0.2

T3 Time point Upw-Spp

T4 Lpw-Spp

Fig. 4 – Changes of pharyngeal airway size after mandibular setback. At the long-term follow-up there is a decrease of upper (’), middle (m) and lower pharyngeal airway size (K).

Fig. 2). At 1 year postoperatively (T3), Upw–Spp was an additional 0.4 mm smaller than at T1, and Mpw–Spp was only an additional 0.1 mm smaller. The sizes of both airway sizes continued to decrease until the end of the follow-up at T4. Between 6 months (T2) and 1 year (T3) postoperatively, the size of the lower pharyngeal airway only increased by 0.6 mm, and the increase continued up to the final follow-up (T4). At T4, Upw–Spp, Mpw–Spp, and Lpw–Spp were smaller than they had been preoperatively. Correlations for total change (T0–T4) of Lpw–Spp and B-point were significant (r ¼ 0.8, Spearman; po0.05). On the other hand, correlations between the total change (T0–T4) of Lpw–Spp and that of hyoid bone position were only weak (r ¼ 0.2, Spearman).

DISCUSSION Most studies investigating skeletal relapse after mandibular setback surgery report follow-ups of 1–3 years. In this study, skeletal relapse of 1.3 mm was measured at pogonion after 1 year, corresponding to 23% of surgical setback. Most other studies, however, used B-point as a reference landmark for skeletal relapse, and found that relapse ranged between 2% and 26% when measured 1–3 years postoperatively (Kobayashi et al., 1986; Sorokolit and Nanda, 1990; Mobarak et al., 2000). In this study, B-point moved even further posteriorly during the first postoperative year and thus showed no skeletal relapse at T3. Between 1 and 12 years postoperatively, B-point relapsed by 0.8 mm in this study. The total

ARTICLE IN PRESS 116 Journal of Cranio-Maxillofacial Surgery

relapse at B-point (T1–T4) was thus only 0.1 mm, corresponding to a surgical setback relapse rate of 2%. Up to now, only one previous study reported longterm results after mandibular setback up to 10 years (Wisth, 1981). This study showed a continuous increase of Sella–Nasion-B-point angle (SNB) during the observation period. Due to differences in fixation and measurement techniques, the results of that study are not fully comparable with ours. Nevertheless, long-term results from both studies show that the process of skeletal relapse––at least measured at B-point––probably occurs over many years following mandibular setback. In accordance with several other studies (Athanasiou et al., 1991; Enacar et al., 1994; Gu et al., 2000; Kawamata et al., 2000), an initially posterior and inferior movement of the hyoid bone was observed. In contrast, Tselnik and Pogrel (2000) have observed an early inferior and anterior movement of the hyoid bone. They suggested that this anterior movement was a physiological adaptation to preserve airway patency. Findings from previous studies with observation periods of between 1 and 3 years are rather variable. In their study, as well as in several previous ones (Enacar et al., 1994; Achilleos et al., 2000; Tselnik and Pogrel, 2000), the postoperative displacement of the hyoid bone was maintained at 1 year postoperatively, whereas others observed a tendency of the hyoid bone to return to its preoperative position (Athanasiou et al., 1991; Gu et al., 2000; Samman et al., 2002). As far as we are aware, our study is the first that presents positional changes of the hyoid bone 12 years postoperatively. The results of this study showed a further anterior and inferior movement during the following 11 years. However, the final position of the hyoid bone was still more posterior than it had been preoperatively. Achilleos et al. (2000) found a significant correlation between the amount of setback measured at pogonion and changes of the hyoid bone 6 months after the operation. In our study, there was also a significant relationship between postoperative changes in position of the hyoid bone and skeletal movements following surgical mandibular setback measured at pogonion and menton. The posterior movement of the hyoid bone, accompanied by the surgical mandibular movement, was visible only at the early postoperative stage. From the first year postoperatively onwards the correlation was, and remained weak until the end of the observation period 12 years later. Several studies have analyzed the stretching of suprahyoidal musculature after mandibular advancement (Carlson et al., 1987; Reynolds et al., 1988). However, there has been only one study (Gu et al., 2000) which reports changes of suprahyoid muscle length after mandibular setback. Gu et al. (2000) reported an increase in length and tension of supraand infrahyoid muscles during a postoperative period of 3 years. The close relationship between suprahyoidal musculature and skeletal relapse found in that

study was assumed to be due to a force that is created to return the muscles to their original resting tension. This is assumed to be capable of moving the mandible anterosuperiorly. In contrast to that study, an initial reduction of suprahyoid muscle length which was significantly related to the amount of mandibular setback was found in this study. Additionally, the continuous increase of muscle length from the early postoperative stage to 12 years postoperatively was related to positional changes of hyoid bone rather than to skeletal changes of the mandible. Based on the results of this study, therefore, it seems that the length of suprahyoid musculature (as measured cephalometrically), only defines hyoid bone position for a prolonged period, but does not contribute to skeletal relapse. This and previous studies showed that pharyngeal airway size decreased as a result of mandibular setback (Riley et al., 1987; Athanasiou et al., 1991; Enacar et al., 1994; Kawamata et al., 2000; Turnbull and Battagel, 2000; Mehra et al., 2001). Six weeks postoperatively, Turnbull and Battagel (2000) reported a significant decrease of retropalatal airway corresponding to our ‘middle’ airway size at the same time point. They assumed that the reduction in middle pharyngeal (retropalatal) airway size was caused by posterior repositioning of the soft palate as a result of increased contact with the dorsum of the tongue when it moved back with the mandible. At the end of the first year of observation, all three pharyngeal airway sizes were still decreased in this study. This is in agreement with several other studies which showed a continuous decrease of lower pharyngeal airway size 1–3 years after mandibular setback (Enacar et al., 1994; Hochban et al., 1996; Tselnik and Pogrel, 2000; Turnbull and Battagel, 2000). In the study of Tselnik and Pogrel (2000), the middle pharyngeal airway also decreased during the 2 years of observation. Only Achilleos et al. (2000) found a slight increase of upper pharyngeal airway size 3 years after surgery. The final results of this study evaluating the longterm effects of mandibular setback surgery revealed that the diameter of the lower pharyngeal airway remained almost unchanged. On the other hand, the sizes of the upper and middle pharyngeal airways continued to decrease with time, and both airway diameters were smaller after 12 years than preoperatively. Whether aging is mainly responsible for this continuous decrease of upper and middle pharyngeal airway size, is not clear. Further studies which anlayse the physiologic aging process in the oropharyngeal complex will be necessary to answer this question. Some previous studies have reported postoperative development of OSAS after mandibular setback, caused by narrowing of the pharyngeal airway (Riley et al., 1987; Hochban et al., 1996; Liukkonen et al., 2002; Samman et al. 2002). The finding of a continuous decrease in the pharyngeal airway size over the long term is in accordance with previous observations that OSAS was diagnosed in connection

ARTICLE IN PRESS Long-term changes of hyoid bone position and pharyngeal airway size 117

with mandibular setback 10–15 years postoperatively (Hochban et al., 1996; Liukkonen et al., 2002). CONCLUSION Following mandibular setback, positional changes of the pharyngeal complex occur in a posterior direction. Over a 12-year postoperative period, the hyoid bone tends to move in an anterior direction, but does not fully regain its original preoperative position. No significant relationship between the length of suprahyoid musculature––measured cephalometrically––and skeletal relapse has been proven in this study. Continuous narrowing of the pharyngeal airway with time is possible. References Achilleos S, Krogstad O, Lyberg T: Surgical mandibular setback and changes in uvuloglossopharyngeal morphology and head posture: a short- and long-term cephalometric study in males. Eur J Orthod 22: 383–394, 2000 Athanasiou AE, Toutountzakis N, Mavreas D, Ritzau M, Wenzel A: Alterations of hyoid bone position and pharyngeal depth and their relationship after surgical correction of mandibular prognathism. Am J Orthod Dentofacial Orthop 100: 259–265, 1991 Carlson DS, Ellis E, Dechow PC: Adaptation of the suprahyoid muscle complex to mandibular advancement surgery. Am J Orthod Dentofac Orthop 92: 134–143, 1987 Enacar A, Aksoy AU¨, Senc¸ift Y, Haydar B, Aras K: Changes in hypopharyngeal airway space and in tongue and hyoid bone positions following the surgical correction of mandibular prognathism. Int J Adult Orthod Orthognath Surg 9: 285–290, 1994 Gu GM, Nagata J, Suto M, Anraku Y, Nakamura K, Kuroe K, Ito G: Hyoid position, pharyngeal airway and head posture in relation to relapse after the mandibular setback in skeletal class III. Clin Orthod Res 3: 67–77, 2000 Hochban W, Schu¨rmann 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 25: 333–338, 1996 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 89: 278–287, 2000

Kobayashi T, Watanabe I, Ueda K, Nakajima T: Stability of the mandible after sagittal ramus osteotomy for correction of prognathism. J Oral Maxillofac Surg 44: 693–697, 1986 Liukkonen M, Va¨ha¨talo K, Peltoma¨ki T, Tiekso J, Happonen RP: Effect of mandibular setback surgery on the posterior airway size. Int J Adult Orthod Orthognath Surg 17: 41–46, 2002 Mehra P, Downie M, Pita MC, Wolford LM: Pharyngeal airway space changes after counterclockwise rotation of the maxillomandibular complex. Am J Orthod Dentofacial Orthop 120: 154–159, 2001 Mobarak KA, Krogstad O, Espeland L, Lyberg T: Long-term stability of mandibular setback surgery: a follow-up of 80 bilateral sagittal split osteotomy patients. Int J Adult Orthod Orthognath Surg 15: 83–95, 2000 Reynolds ST, Ellis E, Carlson DS: Adaptation of the suprahyoid muscle complex to large mandibular advancements. J Oral Maxillofac Surg 46: 1077–1085, 1988 Riley RW, Powell NB, Guilleminault C, Ware W: Obstructive sleep apnea syndrome following surgery for mandibular prognathism. J Oral Maxillofac Surg 45: 450–452, 1987 Samman N, Tang SS, Xia J: Cephalometric study of the upper airway in surgically corrected class III skeletal deformity. Int J Adult Orthod Orthognath Surg 17: 180–190, 2002 Sorokolit CA, Nanda RS: Assessment of the stability of mandibular setback procedures with rigid fixation. J Oral Maxillofac Surg 48: 817–822, 1990 Thu¨er U, Ingervall B, Vuillemin T: Stability and effect on the soft tissue profile of mandibular advancement with sagittal split osteotomy and rigid internal fixation. Int J Adult Orthod Orthognath Surg 9: 175–185, 1994 Tselnik M, Pogrel MA: Assessment of the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg 58: 282–285, 2000 Turnbull NR, Battagel JM: The effects of orthognathic surgery on pharyngeal airway dimensions and quality of sleep. J Orthod 27: 235–247, 2000 Wessberg GA, Schendel SA, Epker BN: The role of suprahyoid myotomy in surgical advancement of the mandible via sagittal split ramus osteotomies. J Oral Surg 40: 273–277, 1982 Wisth PJ: What happened to them? Postoperative survey of patients 10 years after surgical correction of mandibular prognathisms. Am J Orthod 80: 525–535, 1981

Dr. Nicole EGGENSPERGER, MD, DMD Department of CranioMaxillofacial Surgery University of Berne, Inselspital CH-3010 Berne Switzerland Tel.: +41 31 632 33 17 Fax: +41 31 382 02 79 E-mail: [email protected] Paper received 30 March 2004 Accepted 13 October 2004