Abstract
Obstructive sleep apnoea (OSA) is a sleep-related breathing disorder, characterized by repetitive airway obstructions, causing disruptive snoring and daytime sleepiness. Maxillomandibular advancement (MMA), which enlarges the upper airway, is a therapeutic surgical approach. However, no study has performed an upper airway sub-region analysis using validated three-dimensional (3D) anatomical and technical limits on cone beam computed tomography (CBCT). Hence, this prospective, observational trial was performed to evaluate 3D volumetric changes in the upper airway according to validated 3D cephalometric landmarks, before and after MMA, for all patients with a polysomnography diagnosis of OSA (apnoea–hypopnoea index (AHI) ≥5). The secondary objective was to evaluate the impact of MMA on the AHI and in a subjective manner with the Epworth Sleepiness Scale (ESS) and OSA questionnaire. Eleven consecutive OSA patients were included. A significant volume increase in the oropharynx ( P = 0.002) and hypopharynx ( P = 0.02) was observed, in contrast to a non-significant volume reduction in the nasopharynx ( P > 0.05). The median AHI ( P = 0.03) and ESS score ( P = 0.004) decreased significantly as a result of surgery. In conclusion, MMA significantly enlarges the airway volume of the oropharynx and hypopharynx and is associated with improved quality of life.
Obstructive sleep apnoea (OSA) is a sleep-related breathing disorder characterized by repetitive complete (apnoea) or partial (hypopnoea) obstructions of the upper airway during sleep. Implications of OSA are disrupted sleep and daytime sleepiness, and it is associated with a higher risk of cardiovascular, neurological, and perioperative morbidity . OSA is diagnosed by overnight polysomnography and is defined as an apnoea–hypopnoea index (AHI) of five or more apnoea or hypopnoea events per hour .
Besides lifestyle modifications, several non-invasive therapeutic options exist; however, they do not offer a permanent improvement . Continuous positive airway pressure (CPAP) therapy, which prevents collapse of the upper airway, is still considered the primary modality in the treatment of OSA. Compliance, however, is not always optimal due to the cumbersome application. In the case of mild to moderate OSA, an oral appliance such as a mandibular advancement device may be an effective alternative .
On the other hand, several studies reported in the literature have shown that maxillomandibular advancement (MMA) surgery is a procedure that changes the upper airway morphology permanently . This technique has proven to be very effective in the correction of OSA when the maxillomandibular complex is advanced 10 mm or more .
Cone beam computed tomography (CBCT) is an accurate and reliable tool to analyse the upper airway three-dimensionally, due to its high spatial resolution between soft tissue and empty space . Only a few studies have been performed in which the outcome of MMA for OSA treatment has been compared to the three-dimensional (3D) volumetric upper airway changes using CBCT scans. However, these studies did not use validated cephalometric landmarks to divide the different sub-regions of the upper airway. Furthermore, comparing the results from these studies is challenging, as methods for measuring the upper airway sub-regions most often differ . According to a validation study by Guijarro-Martinez and Swennen published in 2013, volumetric measurements of predefined sub-regions of the upper airway are possible using validated 3D anatomical and technical limits on CBCT .
The aim of this study was to assess volumetric changes of the upper airway and its sub-regions following MMA using CBCT scans and validated cephalometric landmarks. In addition, the secondary objective was to evaluate the impact of MMA on quality of life in an objective manner, as measured with the AHI, and in a subjective manner using the Epworth Sleepiness Scale (ESS) and OSA Quality of Life (QoL) questionnaire, and furthermore to correlate these changes with the volumetric changes in the pharyngeal airway sub-regions.
Materials and methods
Patient population
All OSA patients (AHI ≥5) who underwent MMA performed by a single surgeon (NN) between January 2015 and December 2015 were evaluated prospectively. They were initially seen at the sleep clinic for a polysomnography examination to evaluate their AHI upon referral. The decision to perform MMA surgery was made together with an ear, nose, and throat specialist after clinical examination and nasopharyngoscopy. If eligible for surgery, a CBCT scan was done and quality of life questionnaires (ESS and OSA QoL questionnaire) were completed. None of the patients underwent preoperative orthodontic treatment. After approval of the optimal treatment plan, MMA was performed.
Exclusion criteria were patients not eligible according to the criteria given above and morbid obesity (body mass index (BMI) >35 kg/m 2 ). The study obtained local ethics review board approval and all patients provided written consent prior to participation.
Study design
A prospective, observational study was performed. All patients underwent MMA surgery under general anaesthesia by a single surgeon (NN), according to the maxilla-first sequence. A standard Le Fort I osteotomy with linear advancement or counterclockwise (CCW) rotation was performed, and the maxilla was fixed with four L-shaped miniplates (KLS Martin, Tuttlingen, Germany). A bilateral sagittal split osteotomy (BSSO) of the mandible was then performed and fixed with three bicortical screws (KLS Martin) on both sides. An additional chin osteotomy was performed in certain cases.
CBCT scans were obtained both preoperatively and at 4–6 months postoperative using a standardized scanning protocol (i-CAT; Imaging Sciences International, Inc., Hatfield, PA, USA). Vertical scanning was performed in ‘extended field’ mode (field of view (FOV) 17 cm diameter, 22 cm height; scan time 2 × 20 s; voxel size 0.4 mm) at 120 kV (according to DICOM field 0018,0060 KVP) and 48 mA (according to DICOM field 0018,1151 X-ray tube current). Patients were positioned upright and in natural head position (NHP), which is the recommended scanning posture for baseline assessment of the upper airway morphology and dimensions according to the validation study of Guijarro-Martinez and Swennen . The mandible was positioned in centric relation by means of a wax-bite wafer. Such a wafer was used during CBCT scanning preoperatively and postoperatively to create the same distortion on the oropharynx. Patients were instructed to avoid deglutition and any other movement during the CBCT scan .
The DICOM data from the CBCT scan were processed using third-party software (Maxilim v2.2.2.; Nobel Biocare c/o Medicim NV, Mechelen, Belgium). Both pre- and postoperative CBCT data were evaluated by a single investigator (WM) after specific head positioning and virtual orientation. Volumetric measurements (in cubic millimetres, mm 3 ) of validated predefined sub-regions of the upper airway were performed according to the validated cephalometric landmarks as published by Guijarro-Martinez and Swennen in 2013 ( Table 1 ) . These pre- and postoperative CBCT data were also used to calculate the 3D A-point, B-point, and Pog positions. The advancement of the maxilla was measured with the A-point, the mandibular advancement with the B-point, and the chin advancement with Pog.
| Region | Limits | Anatomical | Technical |
|---|---|---|---|
| Nasopharynx | Anterior | Frontal plane perpendicular to FH passing through PNS | = |
| Posterior | Soft tissue contour of the pharyngeal wall | Frontal plane perpendicular to FH passing through C2sp | |
| Upper | Soft tissue contour of the pharyngeal wall | Transversal plane parallel to FH passing through the root of the clivus | |
| Lower | Plane parallel to FH passing through PNS and extended to the posterior wall of the pharynx | = | |
| Lateral | Soft tissue contour of the pharyngeal lateral walls | Sagittal plane perpendicular to FH passing through the lateral walls of the maxillary sinus | |
| Oropharynx | Anterior | Frontal plane perpendicular to FH passing through PNS | = |
| Posterior | Soft tissue contour of the pharyngeal wall | Frontal plane perpendicular to FH passing through C2sp | |
| Upper | Plane parallel to FH passing through PNS and extended to the posterior wall of the pharynx | = | |
| Lower | Plane parallel to FH plane passing through C3ai | = | |
| Lateral | Soft tissue contour of the pharyngeal lateral walls | Sagittal plane perpendicular to FH passing through the lateral walls of the maxillary sinus | |
| Hypopharynx | Anterior | Frontal plane perpendicular to FH passing through PNS | = |
| Posterior | Soft tissue contour of the pharyngeal wall | Frontal plane perpendicular to FH passing through C2sp | |
| Upper | Plane parallel to FH plane passing through C3ai | = | |
| Lower | Plane parallel to FH connecting the base of the epiglottis to the entrance to the oesophagus | Plane parallel to FH connecting the base of the epiglottis to C4ai | |
| Lateral | Soft tissue contour of the pharyngeal lateral walls | Sagittal plane perpendicular to FH passing through the lateral walls of the maxillary sinus | |
At 6 months to 1 year postoperative, a polysomnography examination was performed to re-evaluate the AHI. Surgical cure was defined as an AHI of <5 events per hour and surgical success as a reduction in AHI of ≥50% and an AHI of <20 events per hour after MMA . BMI was also recorded pre- and postoperatively at the sleep clinic.
In addition, patients were asked to complete the ESS and OSA QoL questionnaire for evaluation of their quality of life at these two time-points. The ESS is a short questionnaire primarily validated for OSA, to document the improvement in daytime sleepiness-related symptoms after a therapeutic intervention. The scores for the eight questions (0 = ‘never’ to 3 = ‘high chance of falling asleep’) are added (maximum possible score 24), and higher scores indicate greater sleepiness during common daily activities . The OSA QoL questionnaire evaluates subjective postoperative results after MMA and contains 18 questions, taking 10 min to complete. Questions cover other OSA treatments before MMA, the influence of MMA on several possible OSA symptoms (like daytime sleepiness, snoring, concentration, waking up at night, headache, hypertension, nocturia, and sexual activity), the influence of MMA on facial appearance (scored by the patient and family or friends who join the patient during the consultation), and the influence on self-confidence (from −5 to 0 to +5). It also asks whether the patient would again choose MMA surgery as a therapeutic intervention for OSA with the known beneficial effects.
Statistical analysis
Continuous variables were recorded as the mean ± standard deviation (SD) or as the median with interquartile range (IQR) where appropriate, and categorical variables as proportions and percentages. Different CBCT volume measurements were compared pre- and postoperatively using the Wilcoxon matched pairs test. Correlations were calculated using the Spearman correlation coefficient ( r s ). Multiple backward linear regression was performed to identify factors independently associated with an improvement in AHI. P -values of <0.05 were considered significant. All statistical analyses were performed using IBM SPSS Statistics for Windows, version 22.0 (IBM Corp., Armonk, NY, USA).
Results
Twelve OSA patients underwent MMA by a single surgeon (NN) in 2015. Eleven of these were included in the analysis, as one patient refused to participate. Of the 11 patients included, eight (73%) were male and three (27%) were female; their mean age was 44.7 ± 9.5 years at the time of surgery and their mean preoperative BMI was 26.5 ± 3.5 kg/m 2 .
All 11 patients had bimaxillary surgery, four of whom underwent additional sliding chin osteotomy advancement. The mean planned linear Le Fort I advancement (LFI) was 8.0 ± 2.1 mm, with CCW rotation in nine of the 11 patients. The mean planned linear BSSO advancement was 9.8 ± 1.8 mm and the mean planned additional linear chin advancement was 6.5 ± 1.0 mm ( Table 2 ). On calculating the real advancement using measurements of A-point, B-point, and Pog pre- and postoperatively, a much smaller actual advancement was obtained for the three points. The mean linear A-point advancement was 4.8 ± 2.8 mm, the mean linear B-point advancement was 8.3 ± 2.3 mm, and the mean Pog advancement was 10.03 ± 3.9 mm.
| Age (years) | Sex | Previous OSA therapeutic intervention | AHI preop. | AHI postop. | ESS preop. | ESS postop. | Planned LFI adv. | A-point | Planned BSSO adv. | B-point | Planned chin adv. | Pog | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 36 | M | CPAP | 40.2 | 4.9 | 18 | 6 | 9 | 7.4 | 8 | 9.7 | 0 | 10.5 |
| 2 | 36 | M | CPAP | 27.7 | 11.6 | 14 | 7 | 8 | 3.8 | 10 | 3.1 | 0 | 2.9 |
| 3 | 46 | M | CPAP | 23.6 | 4 | 5 | 0 | 10 | 2.7 | 9 | 8.1 | 6 | 13.3 |
| 4 | 34 | F | None | 11.9 | NA | 21 | 4 | 4 | 0.9 | 10 | 7 | 6 | 8.3 |
| 5 | 57 | M | CPAP | 27.9 | 17.1 | 14 | 5 | 10 | 3.9 | 10 | 9.9 | 0 | 10.7 |
| 6 | 50 | M | MRD, CPAP | 15 | 6.9 | 16 | 5 | 8 | 5.9 | 9 | 5.9 | 0 | 4.9 |
| 7 | 29 | M | MRD | 50.7 | 0 | 4 | 2 | 10 | 6.5 | 11 | 10.7 | 0 | 11.8 |
| 8 | 53 | M | None | 16.9 | 16.9 | 14 | 10 | 6 | 7.5 | 10 | 8.4 | 0 | 7.2 |
| 9 | 55 | M | CPAP, UPPP | 34.9 | 49.6 | 23 | 10 | 5 | 2.7 | 10 | 9.9 | 0 | 11.1 |
| 10 | 45 | F | None | 10.9 | 1.8 | 10 | 7 | 8 | 1.9 | 14 | 8.5 | 6 | 15.1 |
| 11 | 51 | F | CPAP | 34.6 | 10.1 | 16 | 7 | 10 | 10 | 7 | 10.2 | 8 | 14.5 |
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