Maxillomandibular Advancement

Maxillomandibular advancement (MMA) for the treatment of obstructive sleep apnea (OSA) has remained a reliable and highly effective surgical intervention since its introduction in 1989. Modifications have been made to maximize skeletal movement and upper airway stability without compromising facial balance. Contemporary indications of recommending MMA prior to other soft tissue surgery are described. MMA poses unique challenges to surgeons. There are patient-related factors, including OSA, a chronic inflammatory condition with associated cardiovascular and metabolic comorbidity. Perioperative management is more complex than routine orthognathic patients. Key details are shared from a 3-decade experience at Stanford.

Key points

  • Maxillomandibular advancement (MMA) demonstrates consistently high surgical success and modest cure rates for patients with obstructive sleep apnea (OSA).

  • Indications for MMA as first-line surgical treatment include patients with preexisting dentofacial deformity, severe OSA, and airway collapse pattern (complete centric at velum, and complete at lateral pharyngeal wall) examined by drug-induced sedation endoscopy (DISE).

  • MMA involves a counterclockwise rotation with the center at the maxillary buttress to maximize airway muscle tension and balance facial esthetics.

  • Technique modifications from routine orthognathic surgery for MMA are important to address both surgical and patient related factors.

Video content accompanies this article at www.oralmaxsurgeryatlas.theclinics.com .

Introduction: nature of the problem

Since the authors’ first review of 40 patients undergoing maxillomandibular advancement (MMA), a procedure pioneered at Stanford Hospital for the treatment of obstructive sleep apnea (OSA), MMA has remained one of the most effective and reliable surgical intervention for OSA, with its high surgical success rate.

In the early years, MMA was part of a 2-phase algorithm where phase 1 (palate, nasal, tongue base procedures, hyoid advancement, and genioglossus advancement) was followed by phase 2 (MMA) in cases of treatment resistance. The earliest indications for MMA included severe OSAS, morbid obesity, severe mandibular deficiency, and failure of other forms of therapy.

Today, selection criteria for MMA includes the use of dynamic examination, such as drug-induced sleep endoscopy (DISE). MMA is particularly effective in treating OSA patients with lateral pharyngeal wall and concentric velum collapse during DISE. Severe OSA patients with this collapse pattern tend to have low hyoid position, as shown with sleep MRI. Because concentric collapse of the velum is contraindicated in upper airway (hypoglossal) stimulation, and lateral pharyngeal wall collapse is difficult to address with soft tissue pharyngeal procedures, MMA can be a first-line recommendation in OSA patients with this dynamic airway collapse pattern.

MMA is also performed in OSA patients with dentofacial deformity. However, in patients with Class 1 skeletal relationship, MMA with airway-specific counterclockwise (CCW) rotation can be expeditiously performed with minimal orthodontic decompensation.

The role of MMA in reducing the burden of disease in OSA is an important distinction from previous representations where surgical cure was the primary outcome. A favorable outcome is one that mitigates patient symptoms and comorbid risk, with improved quality of life reflected by high levels of patient satisfaction. MMA need not be the only intervention; the authors have performed soft tissue pharyngeal surgery and hypoglossal nerve stimulation to achieve overall treatment success (cure).

There are ample texts that describe the basics of jaw surgery which involve Le Fort I and sagittal split osteotomies. This Atlas article focuses on key steps that define the Stanford MMA. These steps are founded on 3 decades of experience with Nelson B. Powell and Robert W. Riley. Contemporary extension of their philosophy from breathing-focused to bite (brevity of orthodontic treatment with surgery-first protocol) and beauty (balance of facial proportions including nasal form and function) by Stanley Y.C. Liu is also highlighted.

Surgical technique

Preoperative planning

Appropriate patient selection begins with a thorough history, subjective questionnaires (Epworth Sleepiness Scale and Nasal Obstructive Symptom Evaluation), head and neck physical examination, polysomnography interpretation, and fiberoptic nasopharyngoscopy observation. Selectively DISE is used. These objective and subjective examinations can be used in combination with CT imaging to identify appropriate skeletal surgery patients and plan procedures.

The most unique aspect of today’s Stanford MMA in preoperative planning is the center of rotation for the maxillomandibular complex (MMC). Although it is a CCW rotation, the center of rotation is uniquely placed to maximize both airway stability and facial esthetics. Additionally, the main reference points and movements for planning are (1) advancement from a point at the piriform rim just below level of the inferior turbinate, (2) degree of occlusal plane change dictated by the maxilla, and (3) postoperative position of the pogonion. If patients also exhibit dentofacial deformity, this is certainly addressed, but the general principle of movement, as described here remains consistent.

Prior to virtual surgical planning (VSP), Riley and Powell performed what is commonly described in the cosmetic maxillofacial literature as a single-splint technique. This requires extensive experience to control the pitch, roll, and yaw of the MMC and is difficult to reproduce consistently by junior surgeons.

With VSP, surgical movements are planned, and 2 intermediate splints are usually produced to maximize the freedom to balance facial and airway position intraoperatively. Regarding the movement, a differential anterior impaction is performed with the rotation center in line with the buttress. CCW rotation has been described with centers at the anterior nasal spine (ANS) or posterior nasal spine (PNS). The buttress may seem like a peculiar landmark. The rationale is that when the maxilla is rotated in line with the buttress and the level of first molar is maintained, the CCW rotation actually brings the entire maxilla posterior to the original piriform rim. From here, an advancement of approximatley 3-mm to 5-mm anterior to the piriform translates to a final pogonion position approximately 12-mm to 18-mm anterior and 2-mm to 4-mm superior to its original position. The maxillary occlusal plane rotates in CCW direction by approximately 6° to 10°. Attention is given to correction of concurrent orthognathic problems if present (ie, mandibular asymmetry or class 2 or class 3 discrepancy). Notice that the surgery is not planned based on classic cephalometric measures, such as the SNA and SNB. The MMA movements, as described here advance and rotate the MMC to optimize airway and esthetic outcome.

In the representative VSP plan shown in Fig. 1 , there is an occlusal plane change of 11° in a CCW fashion. This is planned via a 3-mm impaction at the piriform rim, while keeping the center of rotation at the buttress. The maxilla is then advanced just 5-mm anterior to the piriform rim. This movement results in a 12-mm advancement at the incisor, 7.6-mm advancement of the A point, 15.7-mm advancement of the B point, and a 23.5-mm advancement of the pogonion ( Fig. 1 ).

Fig. 1
VSP with CCW rotation centered at buttress ( left panel, Before MMA; right panel, After MMA).

This MMA patient in Fig. 2 underwent a similar movement. Due to the relatively small change at the midface coupled with piriformplasty and intraoperative septoplasty, his midfacial balance is not compromised. At the same time, note the significant advancement of the mandible, which is discernible both in the clinical photo and the immediate postoperative CT in the lateral view ( Figs. 2 and 3 ).

Fig. 2
MMA patient before ( left panel ) and after ( right panel ).

Fig. 3
Postoperative CT after MMA. Suspension wires are removed 6 weeks after surgery.

Preparation and patient positioning

There are 2 important nuances to the positioning of the MMA patient compared with the orthognathic patient.

Classically, nasal RAE tubes are popular for orthognathic cases. OSA patients, however, tend to have longer airways. This requires a longer tube, but the longer RAE (Ring, Adair and Elwyn) tubes have larger diameter lumens. This significantly distorts the nasal anatomy such that intraoperative septoplasty and piriformplasty are difficult to perform with accuracy. Instead, the authors use the microlaryngoscopy tube (MLT), where there is adequate length, and thinner diameters, such as a 5.0 mm or 6.0 mm. The authors trim back the tube toward the nares and place a 120° reverse metallic attachment, followed in-line with an accordion extension.

Patients are not placed on a shoulder roll because this tends to further extend the neck. The authors leave patients in their natural head position. This is important for control of the occlusal plane change ( Fig. 4 ).

Fig. 4
Nasal intubation 120° metal connector.

Anesthetic approach/sedation agent

Total intravenous anesthesia with agents such as propofol and remifentanil, is used. Although controlled hypotension with a target mean arterial pressure of 60 mm Hg is recommended for orthognathic procedures, in reality many MMA patients have significant cardiovascular comorbidities. Keeping the mean arterial pressure this low is both difficult for the anesthesiologist and contraindicated for some of the patients. The authors still aim for a brief period of controlled hypotension during maxillary down-fracture but most often are doing this at a mean arterial pressure of approximately 80 mm Hg. Total blood loss is approximately 250 mL to 350 mL for the procedure.

Although the authors’ severe OSA patients are observed in the ICU for the first evening, all patients are extubated at the end of procedure. The authors work closely with anesthesia colleagues during extubation to help with nasal and oral suctioning. Postoperatively, the MMA patients are placed in light guiding elastics with no intraoral splint. This allows easy mouth opening in an emergent situation.

Surgical procedure

Approach to general aspects of MMA surgery is not discussed in detail. Instead, critical key steps are highlighted.

At the time of Le Fort I osteotomy, a wedge is created that determines the degree of CCW rotation. An appropriate degree of CCW rotation should not compromise incisor show in the final maxillary position.

The maxilla is never mobilized aggressively with instruments like the Rowe disimpaction forceps (Sklar Surgical Instruments, West Chester, PA). With a wire through the anterior nasal spine area to control the maxilla, lateral forces are applied concurrently to the posterior maxillary wall to mobilize the maxilla ( [CR] ). The usual anterior pull by the disimpaction forceps is especially ineffectively against previously operated soft palate. Large degree of torque by the disimpaction forceps is also uncontrolled, particularly in the average MMA patient, who tends to be an older adult.

With large CCW rotations, muscle tension associated with the maxilla and mandible is significant. For this reason, maxillomandibular fixation prior to rigid fixation is performed with the aid of suspension wires. The authors use suspension wires anchored to the alveolus with a 2.0-mm screw and through a hole by the piriform rim above the Le Fort osteotomy for the maxilla, and to the arch wire for the mandible. Maxillomandibular fixation prior to fixation with the use of 24-gauge wires on dental brackets or the arch bar would debond brackets or shift the arch bar. Minor discrepancy greatly affects accuracy of the final fixation.

The authors do not perform sagittal split osteotomy with instruments like Smith spreaders. Older patients tend to have little bone marrow space. With the need of longer osteotomy (anterior extent to the second premolar) for fixation after large advancements, the use of Smith spreaders lead to poorly controlled fractures. Instead, the authors focus on an accurate horizontal osteotomy just beyond the lingula, anterior osteotomy not past the inferior midline of mandible, and a wedging open of segments with 3 osteotomes in a sequential sandwiched fashion ( Fig. 13 ).

Finally, with fixation, the authors use 2 to 3 bicortical fixation screws, coupled with a long 2.4-mm plate across the osteotomy site. The rigidity allows the patient a rapid return to function. Patients generally are not kept in a splint, and only light guiding elastics are used immediately after surgery. This allows MMA patients to breathe orally in the immediate post-operative period. By the end of the second week postoperatively, patients begin a pureed to soft diet. Minimal use of narcotic pain medications is expected.

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Jan 19, 2020 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Maxillomandibular Advancement
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