Cephalometric analysis of modifications of the pharynx due to maxillo-mandibular advancement surgery in patients with obstructive sleep apnea

Abstract

Cephalometry has been used to measure hard and soft facial tissues, as well as the pharyngeal air space for the diagnosis of obstructive sleep apnea (OSA). The changes occurring in the pharynx due to maxillo-mandibular advancement (MMA) have not been established or quantified. The objective of this study was to identify the anatomical changes of the pharynx and of hard tissues that occur in patients with OSA after MMA. 19 patients with a polysomnographic diagnosis of OSA were submitted to cephalometric analysis before and 6 months after surgery in order to evaluate the changes produced by MMA in the pharynx and soft tissues. Cephalometry was standardized in order to obtain descriptive measurements of the dimensions of the airways, the position of the hyoid bone, and maxilla-mandibular relations. The modifications of the pharynx due to MMA showed a significant relation obtained by cephalometry. For each millimeter of maxillary and mandibular bone advancement there was a 0.76 mm increase in the retropalatal region and a 1.2 mm increase in the pharynx in the retrolingual region. In addition, MMA promoted a significant repositioning of the hyoid bone in the cranial direction.

Obstructive sleep apnea (OSA) is characterized by repetitive episodes of airway obstruction during sleep usually associated with sleep interruption and a fall in oxyhemoglobin saturation. OSA is linked to significant morbidity and mortality and has been associated with increased cardiovascular risk, insulin resistance, metabolic syndrome, excessive daytime somnolence and automobile accidents. Patients also show cognitive changes (worsening of memory and concentration, mood changes and loss of motivation) with an increasing worsening of quality of life.

The physiopathology of OSA has been related to predisposing anatomical factors such as craniofacial abnormalities, macroglossia, hypotonia of soft tissues of the oropharynx, retroposition of the base of the tongue, mandibular hypoplasia and retroposition, and maxillary retrusion.

Cephalometry has been used to determine partial retrusion of the whole face as well as of the air space of the pharynx for the diagnosis of OSA. The changes produced in the pharynx by maxillo-mandibular advancement (MMA) have not been fully established. With this method it is possible to evaluate the position of facial bone structures and soft tissues with adequate precision. The degree of development of the maxilla and mandible is important; if bone deficiency is present there may be a higher incidence of obstruction at the level of the soft palate or of the base of the tongue.

OSA is associated with statistically significant cephalometric changes in patients with the disease compared to a control group. Narrowing of the airway is involved in the development of OSA and studies have shown that a reduction of the transverse area of the pharynx increases the risk of collapse.

Surgical techniques for the modification of the position of the maxilla and mandible are used for the treatment of facial skeletal deformities, but the exact effect of this bone repositioning on the morphology of the upper airways in patients with OSA is not known. Some authors think that surgery for mandibular advancement also provokes an advancement of the lingual and suprahyoid muscles inserted in the mandible and that surgical advancement of the maxilla leads to repositioning of the velum and of the velopharyngeal muscles. This is thought to cause an increase in the air space, which seems to improve the permeability of the airway, although it is not possible to quantify the relationship between the amount of bone modification and the secondary repositioning of the soft tissues. Establishing a relationship between maxilla-mandibular bone advancement and increased air space should be useful for surgical planning in order to re-establish a normal pharyngeal air space.

MMA has been described as the most effective surgical treatment for OSA, with success rates above 90%. Most studies have been conducted to confirm the efficiency of this treatment modality but few have described the anatomical changes produced by the surgery in the pharynx.

The objective of the present study was to identify by cephalometric analysis the anatomical changes of the pharynx and hard tissues that occur in patients with OSA after MMA.

Materials and methods

The study was conducted on 19 patients (14 males and 5 females) with a diagnosis of OSA syndrome (OSAS) submitted to treatment with MMA. The inclusion criterion was polysomnographic confirmation of OSAS determined by an apnea/hypopnea index (AHI) of more than five events per hour. The research protocol was approved by the Research Ethics Committee of the Institution (protocol no. 6245/2006) and all patients gave written informed consent to participate.

All patients were submitted to MMA for the treatment of OSA using Le Fort I type osteotomy for the advancement of the maxilla and bilateral sagittal osteotomy for the advancement of the mandible. All patients were operated on by the same surgeons and received pre- and postoperative orthodontic treatment. The osteotomies were stabilized with rigid internal fixation. Polysomnography and cephalometry were performed preoperatively and 6 months after surgery.

Polysomnography was performed in the sleep laboratory with a full night recording and patient admission between 19:00 and 20:00 h and discharge at 7:00 h on the next day. In the sleep laboratory, the patients responded to a standard questionnaire before and after the recording. The examinations were recorded with a digital biologic polysomnograph (Poliwin 2000 program) with a minimum recording time of 5 h. The variables studied were grouped into standard assemblies internationally proposed for polysomnography.

Regarding cephalometry, two lateral teleradiographs were obtained for each patient at different times (preoperatively, T1; and postoperatively, T2). The routine of the radiographic examination was standardized to obtain lateral teleradiographs. The procedure was performed by the same technician always using the same apparatus. Part of this standardization was the visualization of the lingual contour using barium sulfate contrast applied to the median sulcus of the patient’s tongue with a cotton swab. This procedure permitted the authors to contrast the contour of the tongue, which is often not visualized when the conventional technique is used.

The radiograph was obtained with the patient standing in a lateral position, 90 degrees in relation to the apparatus, with the position of the head being maintained with a cephalostat. The distance of 1.55 m between source, object and film minimized the distortions of the radiographic image. The patients were instructed to keep their teeth in occlusion, with lips sealed and tongue relaxed on the floor of the mouth, without swallowing. The radiograph was obtained at the final phase of expiration. The teleradiography tracings (T1 and T2) were performed by the same investigator.

Cephalometric analysis

The study was based on cephalometric analysis of lateral teleradiographs obtained by a standard technique ( Fig. 1 ). The authors used the habitual tracing with a standardized technique to obtain the following measurements. First, SNA, the angle formed by the joining of the sella, nasion and A point. This angle shows the position of the maxilla in relation to the anterior base of the skull, thus defining the degree of protrusion or retrusion of the maxilla in the anteroposterior direction. Second, SNB, the angle formed by the joining of the sella, nasion and B point. The amplitude of this angle indicates the position of the mandible in relation to the anterior base of the skull, thus demonstrating the degree of protrusion or retrusion of the mandible in the anteroposterior direction. Third, Mp, the mandibular plane, a plane constructed from the gnathion (Gn) to the gonion (Go). Fourth, Mp–H, the linear distance along a perpendicular line from point H to the mandibular plane (Mp). Fifth, PAS, the lower pharyngeal airway space related to the retrolingual airway space. The linear distance between a point on the base of the tongue and a point on the posterior pharyngeal wall, both determined by the extension of the B–Go line. Sixth, AA–PNS, the bone oropharynx defined as the linear distance between the atlas vertebra (AA) and the PNS. Seventh, UPPhW–PP1, the upper pharyngeal space related to the retropalatal airway space. The linear distance between the Upphw point and the PP1 point determined from the projection of the PNS–ANS line in the pharynx. Eighth, C3–H, the linear distance between points C3 and H, essential for the verification of the positioning of the hyoid bone. Ninth, C3–Me, the distance between points C3 and Me. Tenth, Go–Me, the distance between points Go and Me. It refers to the effective length of the mandible.

Fig. 1
Lateral teleradiograph with visualization of the lingual contour by means of barium sulfate contrast and cephalometric tracing with reference points and lines. Point S, sella; Point N, nasion; Point A, subspinal, located in the deepest point of the curvature between the anterior nasal spine and the alveolar bone; Point B, supramental, located in the deepest point of the anterior surface of the contour of the mandibular symphysis; Point ANS, anterior nasal spine; Point PNS, posterior nasal spine; Point UpphW, upper point of the posterior wall of the pharynx; Point PP1, upper palatal point; Point AA, most anterior point of the atlas vertebra; Point C3, most anterior and inferior point of the third cervical vertebra; Point Gn, gnathion; Point Go, gonion; Point H, hyoid; Point Me, mentonian.

Statistical analysis

Exploratory analyses of the data were first performed. The nonparametric Wilcoxon test for paired data was used to compare the cephalometry variables before and after surgery. The null hypothesis of this test is that the two samples have the same distribution. The graphs were prepared with the R software, version 2.6.2. The results are listed in the tables.

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Jan 24, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Cephalometric analysis of modifications of the pharynx due to maxillo-mandibular advancement surgery in patients with obstructive sleep apnea
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