Asian Malar and Mandibular Surgery Treatment & Management
- Author: Charles S Lee, MD, FACS; Chief Editor: Jorge I de la Torre, MD, FACS more...
No medical therapy is available for zygomatic reduction. For mandibular prominence, botulinum toxin (BOTOX®) has been shown to be effective therapy in patients with a large muscle component. The duration of effect is currently under evaluation. Occlusal splints and other therapies have not met with consistent results.
Several publications now report on the effectiveness of botulinum in reducing the size of the masseter muscle.[9, 10, 11, 7, 12] In higher doses, permanency has been obtained. The earliest studies published from abroad have used Dysport, which is not yet available in the United States. According to a 2009 Cochrane Database review, well-designed, adequately powered, randomized controlled clinical trials are needed to study the effects of BOTOX® injections as treatment for bilateral benign masseter hypertrophy.
Optimal dosage for reducing the size of the masseter muscle is under investigation. Currently, the most common dose in the author's clinic for (BOTOX®) to the masseter muscle is 15-50 IU per side.
The patient is evaluated to locate the area of concern. If only the body is involved, burring the prominent portion through an intraoral incision may suffice. Wide subperiosteal dissection can lead to malar soft tissue ptosis. To prevent this, the soft tissue should be supported by suturing to the periosteum or through a drill hole along the infraorbital rim. If the arch contributes to the problem, as is usually the case, a coronal approach is frequently used. The author currently favors the coronal approach to preclude problems with malar soft tissue ptosis. The coronal approach also affords less risk to the frontal nerve as compared to a limited incision approach to the zygomatic arch.
Prominent mandibular angle
The cause of the bony prominence is determined by evaluation of the patient and radiographs. The lateral flare can be reduced using a sagittal saw or bur through an intraoral incision. The lateral flare can occur in conjunction with a prominent posterior bony angle, which is removed using a Stryker oscillating saw through an intraoral incision. Once the radiographic template of the desired resection has been marked on the bone, make the first cut at the superior (cephalic) border of the template along the posterior border of the ascending ramus. This controlled cut prevents going too high on the ascending ramus, which would risk a subcondylar fracture. After this first cut, the contouring is continued by 3-4 straight-line ostectomies, each cut moving down the mandible toward the symphysis as previously marked, followed by smoothing out of the overlapping cuts.
Frequently, the prominence is not limited to the jaw angle, but involves the entire mandibular body. Alternatively, the angle is difficult to visualize because of the prominence of the body. In such cases, the outer cortex of the mandible is removed, in a manner described as a sagittal split ostectomy.
Radiographs are reviewed and asymmetries noted. The relationship of the mandible is also assessed because correction of the zygoma may make the mandibular angle appear more prominent. Counsel the patient appropriately. Examination of the radiograph and the physical examination findings helps determine which components of the zygoma need to be addressed. If prominence is isolated to the body or the anterior portion of the arch, an intraoral approach suffices. If the zygomatic arch is involved, a coronal approach is necessary to adequately address the prominence.
A Panorex radiograph helps delineate the course of the inferior alveolar nerve and the amount of bone that can be safely removed. If the mandibular angle is square, a plan can be made to convert it to a more obtuse angle by using a right-angle saw to remove bone from the posterior mandibular border. If the primary problem is width from a frontal view, the lateral cortex of the mandible can be burred.
Full exposure of the arch and body of the zygoma is obtained through a coronal approach. Using a sagittal saw, the first osteotomy is performed at the junction of the body and arch of the zygoma. A second osteotomy is made at the arch, staying anterior to the zygomatic tubercle so that the temporomandibular joint is not violated. The osteotomized segment is repositioned cephalically, usually approximately 2 cm, and secured using wires or miniplates. The arch segments are overlapped, so that the free bone segment lies underneath the fixed segment of the arch. Bone edges at the arch and the body are burred down to prevent a step-off. A drain is placed, and the temporal fascia is sutured. An ellipse of scalp is excised prior to closure with staples, in a vector corresponding to the lateral brow–malar soft tissue junction, to help prevent cheek ptosis. See the image below.
Alternatively, a complete transection of the posterior cut followed by a greenstick infracture of the anterior cut can adequately reduce the zygoma without the need for plate or wire fixation. This technique has become the author's preferred technique.
An intraoral incision is made along the anterior edge of the ramus, and a subperiosteal dissection is performed. Sharp dissection using a knife or cautery is used to detach the muscle along the inferior posterior border of the mandible. To improve width, a large bur is used to reduce the protruding bone. Alternatively, a Lindemann spiral bur can be used to score or mark the desired bony excision, and then a chisel can be used to split off the offending bone fragment. A right-angle saw can be used to reduce the posterior border of the mandible to create a more obtuse angle. Of utmost importance is to protect the soft tissue at all times when using power drills or osteotomes in this highly vascular area. Bleeding from the facial artery can be difficult to control. An external incision may be necessary to control vessels that may retract under the mandible. The images below show a patient before and after surgical reduction of the mandibular angle.
If access to the angle is obscured by the body of the mandible or if the patient has a prominent mandibular body, then a sagittal split ostectomy is performed. The outer cortex of the mandible extending from the angle distally to the mental foramen mesially is resected. Bone wax may be needed on occasion. The image below shows the outer cortex of bone that has been removed.
Alternatively, a retromandibular approach can be used. An incision is made along the inferior half of the auriculo-mastoid sulcus, ending at the posterior border of the lobule. Subcutaneous dissection is followed by a vertical incision through the superficial musculo-aponeurotic system (SMAS) along the posterior border of the mandible. This is followed by blunt dissection of the posterior border of the parotid gland and retracting it anteriorly. The pterygomasseteric sling is identified and incised along the posterior border of the mandible, extending from the angle of the mandible upward 2 cm. Care is taken to avoid the facial nerve; the retromandibular vein is retracted posteriorly. A subperiosteal dissection covers the area extending from just above the occlusal plane to slightly mesial to the anti-gonial notch.
The dissection continues around the border (knife dissection is required at the angle) and onto the undersurface of the mandible for 2 cm to clear the area for the osteotomy. Under direct vision, the reciprocating saw is used to resect the proposed area of bone. One or several osteotomies are used to create the desired curvature to the angle. The limiting factor on bone resection is the inferior alveolar groove, which is checked by Panorex, taking in to account the 20% magnification at the mandibular angle. The usual dimension of bone resected is 15 mm x 40 mm. A drain is placed (removed 2 d later) and an anatomical closure is afforded, with a watertight SMAS closure to prevent a parotid fistula.
Compressive dressings and drains are removed on the first postoperative day. Every other staple is removed on the third day, and the remainder of staples are removed on the seventh day. A soft diet is advanced as tolerated by the patient. Postoperative pain is mild to moderate. Swelling resolves enough for the patient to return to work approximately 10 days after the procedure.
Postoperative trismus is to be expected, and exercises to stretch the masseter muscle should begin after 1 week. Compressive dressings are worn for 1 week. The diet is advanced from a clear diet the first day, to a liquid diet for the first week, and then to a soft diet for another week.
Trismus can be significant if the masseter muscle was partially removed as part of therapy. The patient is instructed in mouth opening exercises for the first 2-3 weeks.
The frontal nerve can occasionally be injured during the coronal approach. Traction injuries resolve within 6-12 months. Transection of the nerve requires treatment by denervating the opposite frontal nerve (surgically or with botulinum toxin injection) and/or a hemicoronal lift.
Preoperative asymmetry should be pointed out to the patient. The advantage of a coronal approach to malar reduction is the maximum control over the bone segment and the opportunity to compare both sides simultaneously. Persistent postoperative asymmetry may necessitate reoperation.
A mild degree of step-off can occur. This can be minimized by burring down the contact surfaces of bone.
The marginal nerve lies in a plane superficial to the masseter muscle. The nerve is potentially at risk during resection of the masseter muscle or during the use of power instruments without adequate protection.
The facial artery lies at the anterior border of the masseter muscle. The subperiosteal dissection must remain in the proper plane. In addition, when using a power instrument, protection of the soft tissue is critical to the safe execution of the operation.
Subcondylar fracture can result from an unfavorable fracture line extending from the angle of the mandible. A horizontal back-cut along the posterior border at the superior limit can reduce this risk.
Future and Controversies
The alternative to a coronal approach reposition operation is an intraoral approach to bur down the malar prominence and to create an anterior osteotomy, combined with a preauricular approach to complete the posterior osteotomy. Symmetry may be harder to obtain through this route, and malar soft tissue ptosis may occur.
The masseter muscle may be removed as part of the operation. From a frontal view, the muscle can contribute significantly to mandibular prominence. Some believe that removal of the bone alone changes the dynamics of masseter muscle contraction and leads to thinning of the muscle by disuse atrophy. Others believe that the muscle should be resected to achieve maximal effect.
The use of botulinum toxin to reduce the hypertrophy of the masseter muscle will play an important role in the future. Although the boney prominence remains, the reduction of muscle thickness significantly improves the appearance of the mandibular angle.
The use of botulinum for masseter hypertrophy is quickly becoming the treatment of choice for mild to moderate forms of prominent mandibular angles. Surgery is preferred for more severe situations or for patients who prefer to avoid repeated injections to the masseter.
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