1 INTRODUCTION

Obstructive sleep apnea syndrome (OSA) results from partial or total obstruction of the upper airway during sleep due to narrowing or total obstruction of the upper airway. The airway narrowing or collapse necessitates the patient to increase his/her negative intrathoracic pressures during sleep which results in sleep fragmentation and excessive daytime somnolence as well as a decrease in life expectancy, increased risk for hypertension, myocardial infarction and cardiac arrhythmia.

Maxillofacial skeletal abnormality is a well-recognized predictor in OSA. Maxillomandibular deficiency results in diminished airway dimension which leads to nocturnal obstruction.^1,2 Currently, the most effective surgical procedure in the management of OSA is the expansion of facial skeleton by advancing the maxilla and mandible, i.e. maxillomandibular advancement (MMA). MMA achieves enlargement of the pharyngeal and hypopharyngeal airway by physically expanding the skeletal framework. In addition, the forward movement of the maxillomandibular complex improves the tension and collapsibility of the suprahyoid and velopharyngeal musculature. Lateral pharyngeal wall collapse, which has been shown to be a major factor in airway obstruction,³ is also shown to be lessened following MMA.⁴ The current MMA technique involves the use of maxillary Le Fort I osteotomy and mandibular sagittal split osteotomy to facilitate the forward movement of the maxillomandibular complex followed by the application of rigid fixation.⁵

Since the early recognition of the role of maxillofacial skeletal deformity in OSA, all of the emphasis of deformity recognition and treatment has been primarily limited to the sagittal plane. The transverse deficiency of the maxilla and/or mandible as a potential contributor and treatment of OSA has received little attention. Recently, the constriction of the maxilla has been suggested as a possible risk factor of OSA. In a comparative study between OSA and control subjects by Seto et al.,⁶ OSA subjects were found to have narrower, more tapered and shorter maxillary arches. Kushida et al.⁷ found that the intermolar distance of the maxilla is related to the presence of OSA. Cistulli et al.⁸ have reported that patients with Marfan’s syndrome, in which maxillary constriction is a common finding, have increased incidence of OSA and elevated nasal resistance. The relationship of nasal resistance and maxillary morphology has long been suggested in the orthodontic literature.

Despite the past success in conventional maxillofacial surgery for the treatment of airway obstruction, there is increasing interest in the use of distraction osteogenesis for skeletal expansion in treating OSA due to its feasibility in the pediatric population as well as the less invasive nature of the procedure. This chapter will discuss the method as well as relevant results.

2 DISTRACTION OSTEOGENESIS IN THEMAXILLOFACIAL REGION

Skeletal expansion by slow osseous distraction (distraction osteogenesis) is not new and has been previously studied extensively in orthopedic surgery. It has demonstrated acceptable feasibility, efficacy, safety, and reproducibility of its treatment results. In its simplest form, distraction osteogenesis (DO) describes the generation of new bone in the stretched fracture callus. A screw-driven appliance that is firmly attached to the bone fragments slowly pulls apart the cut/or fractured bony edges, and new bone can fill in the stretched callus tissue. DO was first described by Alessandro Codvilla in 1905, who first published the use of this technique in lengthening the long bone.⁹ However, it is Ilizarov who is credited with developing the current methods of DO.¹⁰ DO in the maxillofacial region was first investigated by Snyder et al.¹¹ in the canine mandible. Karp et al.¹² demonstrated that bone formation during DO in the maxillofacial region is similar to that of long bones, which is predominantly by intramembranous ossification. Surgical lengthening by DO in sagittal plane was first described by McCarthy, who reported on the application of DO of the human mandible in pediatric patients in 1992.¹³ The surgical expansion of the maxilla and mandible to increase the width by distraction osteogenesis was reported by Bell and Epker¹⁴ and Guerrero,¹⁵ respectively.

DO is a potentially new approach for the treatment of OSA by slowly expanding the mandible and/or the maxilla in the sagittal or frontal plane, thereby expanding the airway. This technique is less invasive than the traditional technique. It requires less tissue manipulation, less blood loss, and has less skeletal relapse potential.

3 BRIEF DESCRIPTION OFMAXILLOMANDIBULAR ADVANCEMENT

See Figure 54.1.

Fig. 54.1 Pre- and postoperative cephalometric radiographs and panoramic radiographs.

The procedure is performed in the operating room under general anesthesia technique. The maxillary advancement is a Le Fort I osteotomy. The procedure is modified for DO with the placement of bilateral maxillary distraction devices following a limited down-fracturing of the maxilla without extensive mobilization. In the mandible, the procedure consists of performing an osteotomy behind the last molar, followed by application of the intraoral distraction device. Following 5–7 days of latency period, the device will be activated two to four times per day to achieve 1 mm of bone lengthening per day. The total bone lengthening will be determined preoperatively based on the patient’s anatomy, dentition, facial appearance and the severity of OSAS. After the completion of distraction (approximately 1–3 weeks), the distraction devices are maintained in place for 2–3 months to allow bone ingrowth and healing. The distraction devices are then removed under either general anesthesia or intravenous sedation technique.

4 BRIEF DESCRIPTION OFMAXILLOMANDIBULAR WIDENING

See Figures 54.2 and 54.3.

Fig. 54.2 Progression of maxillomandibular widening.

Fig. 54.3 Pre- and postoperative cephalometric radiograph. Note the increase in airway space behind the tongue base.

In the pediatric population, maxillary widening often does not require surgical intervention since the midpalatal suture can be widened and the maxilla is expanded simply with a distractor placed in the palate. However, after the fusion of the midpalatal suture after adolescence, osteotomy is required to facilitate the expansion. The procedure is performed in the operating room under general anesthesia technique. Maxillary widening is achieved by a limited osteotomy in the Le Fort I level without down-fracturing. A limited osteotomy in the midline of the maxilla is also performed. The distraction device is usually placed by the orthodontist before surgery, and it is activated for 0.5 mm at the completion of the operation. In the mandible, a midline osteotomy is made, followed by application of the intraoral distraction device. Following 5–7 days of latency period, the device will be activated two to four times per day to achieve 1 mm of bone lengthening per day. The total widening will be determined preoperatively based on the patient’s anatomy, dentition, facial appearance and the severity of OSAS. Typically, a widening of 5–10 mm can be achieved. After the completion of distraction (approximately 1–3 weeks), the distraction device will be maintained for 2–3 months to allow bone ingrowth and healing. The maxillary distraction device is removed by the orthodontist, and the mandibular distraction device is removed under general anesthesia.

5 DISCUSSION

DO offers several advantages over the conventional techniques by eliminating the need for bone grafting, and it involves less surgical dissection because bone lengthening is the result of natural bone healing in a gap created by a simple osteotomy. The incremental skeletal movement allows accommodation of the soft tissue, thus enabling large skeletal movement that usually cannot be achieved by conventional techniques. The gradual soft tissue accommodation also improves the stability of the new skeletal position.

The major advantage in the application of DO for maxillofacial skeletal expansion is in the pediatric population where access for the conventional procedure is limited, the volume of bone is insufficient for conventional procedure, there is a need for much greater skeletal expansion than the conventional technique can provide and the potential for surgical scarring by conventional procedure due to the extensiveness of the operation, which can negatively impact future facial growth. Both advancement and widening of the maxilla and mandible have been shown to improve OSA. Maxillary widening improves nasal airway resistance,^16,17 although the beneficial effect of maxillary expansion on nasal resistance may not be uniformly achieved in all patients. It appears that patients with greater degrees of nasal resistance tend to have greater improvement after maxillary expansion.^18,19 Nocturnal enuresis is improved in children.^20,21 Cistulli et al.²² performed maxillary expansion on 10 OSA patients with maxillary constriction and improvement was achieved in nine of the 10 patients. The mean Apnea/Hypopnea Index (AHI) was reduced from 19 events per hour to seven events per hour, and the mean maxillary expansion achieved was 12.1 mm. It is unknown whether mandibular expansion can be performed with maxillary expansion, and if simultaneous maxillary and mandibular expansion can improve OSA. Pirelli et al.²³ treated 31 children with orthodontic maxillary expansion. Nasal resistance was improved in all patients. The AHI was reduced from 12.2 events per hour to less than one event per hour. The mean expansion was 4.32 mm.

There is extensive literature support for the application of DO to advance the maxilla or the mandible. Since the initial report by McCarthy et al.¹³ mandibular advancement by DO in the pediatric population has gained increasing popularity. The majority of the studies have demonstrated impressive success in the management of OSA in pediatric patients with craniofacial syndromes.^24–27 It has become the preferred management in patients who are tracheotomy dependent and the majority of the patients can be decannulated following DO. Contrarily, DO to achieve maxillary or mandibular advancement in the adult population has not gained significant acceptance. Only two centers have reported their experience of DO in the management of adult OSA.^28,29 This is likely due to the increased treatment time required, the presence of distraction devices which significantly affect the patient’s mastication, aesthetics and speech. These unfavorable factors have limited the patient’s acceptance of DO in the adult population.