9: Orthognathic Surgery

Orthognathic Surgery

The practice of orthognathic surgery was popularized in the 1980s, especially after the blood supply of the maxilla became more clearly understood. The procedures have undergone several modifications in surgical technique, administration of anesthesia, and postoperative care. Over the past decade, two factors have influenced the practice of this surgical specialty. First, decreasing insurance reimbursement and limited coverage (at least in the United States) have created economic barriers for patients and surgeons. Second, the introduction of virtual surgical planning and surgery have revolutionized the accuracy and speed of treatment.

Correction of dentofacial deformities using combined orthodontic and surgical treatment can provide dramatic changes in both the cosmetic and functional aspects of the face. Patient commitment to an extended period of treatment and a close working relationship with the orthodontist are essential to a successful outcome.

An important component of the management of patients planning for orthognathic surgery is the correct diagnosis of both dental and skeletal abnormalities. Dental compensation can frequently mask an underlying skeletal deformity. Assessment of the maxilla and mandible should consider the three dimensions: anterior-posterior, vertical, and transverse. Evaluation at each dimension should account for cosmetic factors (e.g., amount of tooth/gingival show or size of the chin), growth abnormalities (hypoplasia or hyperplasia), and asymmetries.

Treatment is tailored to each patient based on the procedure that would achieve the best result while minimizing morbidity. Patient education about the procedure, postoperative healing, and potential complications of orthognathic surgery is by far the most important factor in patient satisfaction.

This section presents four teaching cases that address maxillary, mandibular, and bimaxillary surgery and severe mandibular horizontal hypoplasia treated with distraction osteogenesis surgery. In this new edition we have added two new cases — computer-assisted surgery and the neurologic complications of and microneurosurgery for orthognathic surgery.

Mandibular Orthognathic Surgery

HPI

The patient reports having had braces twice when she was younger, but she notices this did nothing to change the appearance of her chin. She was referred to a different orthodontist, because her general dentist was concerned about the periodontal health of her lower incisors. Previous orthodontia had proclined the lower anterior teeth outside the alveolus, resulting in several millimeters of clinical attachment loss. The patient has completed presurgical orthodontic treatment to reverse the previous orthodontic camouflage and is now ready for surgical correction. She explains that she has difficulty eating foods with the front teeth and has become very self-aware of her retrusive chin and everted lower lip (both functional and cosmetic complaint). She does not have any symptoms of temporomandibular joint (TMJ) dysfunction (TMD) (although a relationship between malocclusion and TMD has been suggested, the scientific evidence is not clear).

Examination

The examination of a patient for orthognathic surgery can be divided into four components: TMJ, skeletal, dental, and soft tissue components. Skeletal discrepancies (hypoplasia or hyperplasia) should be assessed in three dimensions: transverse (horizontal), anteroposterior, and vertical.

The maxillofacial examination of the current patient proceeded as follows.

1. TMJ component

2. Skeletal component

 There is no facial asymmetry.

a. Transverse dimension

b. Anteroposterior dimension

c. Vertical dimension

3. Dental component (occlusion and dentition)

4. Soft tissue component

Imaging

The panoramic and lateral cephalogram are the minimum preoperative radiographs necessary for mandibular orthognathic surgery. The panoramic radiograph allows evaluation of the dentition, the mandibular bony anatomy, and the position of any impacted third molars. Some surgeons recommend surgical removal of the mandibular third molars at least 9 months prior to a sagittal split osteotomy (alternatively, third molars can be removed during the procedure). The PA cephalogram is useful in cases of asymmetry.

Other imaging for orthognathic surgery includes CT scans with conventional and three-dimensional views and videography. These imaging modalities can be useful in complex cases of skeletal asymmetry and cases requiring multiple surgical moves in the maxilla and mandible. There is also software that allows for manipulation of imaging in attempts to predict surgical changes and outcome. (The discussion of these tools is addressed in the section on computer-assisted surgical simulation later in this chapter.)

The lateral cephalogram is the standard film for evaluation of the anteroposterior position of the soft and hard tissue. Measurements of cephalometric norms are used for evaluation of the mandible (and maxilla) in the vertical and anteroposterior dimensions. Most current cephalometric analysis involves comparing the position of the mandible in reference to the cranial base (SNB) and the maxilla (ANB). A variety of other measurements are used to assess the vertical or horizontal abnormalities of the maxillomandibular complex (including teeth). Lateral cephalometric analysis does not assess mediolateral facial parameters. There are different techniques available to analyze a lateral cephalogram, and it is best to be consistent.

For the current patient, the preorthodontic cephalometric measurements and films are shown in Table 9-1 and Figure 9-2.

Treatment

Treatment of mandibular hypoplasia or hyperplasia is dependent on any coexisting maxillary dentofacial abnormalities. If the position of the maxilla is deemed to be appropriate (clinical and radiographic analysis), mandibular surgery alone can be considered, because the final position of the mandible will be dictated by the occlusion and the position of the maxilla. If the maxilla is abnormally positioned, then maxillomandibular surgery is indicated. Setting the mandible anteriorly or posteriorly in the ideal occlusion may produce an unaesthetic chin position. Therefore the need for adjunctive surgical procedures (advancement/reduction genioplasty/submental liposuction/submentalplasty) should be considered, especially in mandibular setbacks.

The basic method of the sagittal split osteotomy has remained unchanged since it was first described in 1955; however, individual surgeons have developed different instrumentations and cutting sequences to complete the surgery. Similarly, practitioners differ in their preference for fixation (i.e., bicortical position screws, lag screws, or one or more rigid fixation plates).

Patients with mandibular asymmetry require special consideration related to correction of the deformity. Surgical implications include the uneven overlap of the osteotomized distal and proximal segments. Similarly, the end position of the chin and the mandibular angles have to be anticipated for optimal results. Bony recontouring, genioplasty, or augmentation at the angles or chin may be required.

The overlying soft tissue response to mandibular osteotomies can be predicted. In general, the soft tissue (chin/lip) response for mandibular advancement or setback is about 90% of the skeletal move (e.g., advancing the mandible 10 mm advances the chin and lip about 9 mm). The status of facial growth also needs to be determined in younger patients. The gold standard for evaluation of facial growth is superimposition of interval (6 months apart) standard lateral cephalograms.

The current patient underwent a bilateral sagittal split osteotomy (Figure 9-3, A), resulting in a 10-mm advancement. The proximal and distal segments were fixated using three bicortical position screws at the superior border (Figure 9-3, B) on each side. Figure 9-4 shows the occlusion 9 months after the completion of surgery and 1 month after removal of the orthodontic appliances. Figure 9-5 shows the postoperative lateral cephalogram.

Complications

Complications of mandibular orthognathic surgery can be categorized into intraoperative, early, and late. The complications related to the sagittal split osteotomy are emphasized next.

Intraoperative. The most common intraoperative complication is an undesirable split or fracture of the segments, reported in 3% to 20% of cases. A common cause of proximal segment fractures is failure to complete the osteotomy at the inferior border, resulting in a free segment. Some proximal segment fractures can lead to fracture propagation up to the condylar head. Confirmation of the continuity of the condyle with the proximal segment detects this fracture. Undesirable fractures can be treated with rigid fixation or a period of 6 weeks of intermaxillary fixation.

Damage to the inferior alveolar nerve is a known complication of the sagittal split osteotomy. When possible, intraoperative transection of the nerve is best treated by immediate epineural repair. Retention of the neurovascular bundle in the proximal segment as the mandible is split is a common cause of injury to the nerve. If the nerve is observed to be in the proximal segment as the mandible is split, it should be gently dissected and positioned along the canal in the distal segment.

Uncontrollable intraoperative hemorrhage is uncommon for mandibular orthognathic surgery in an otherwise healthy patient. However, it can be seen in patients with vascular anomalies or undiagnosed coagulopathies. Damage to the facial artery or retromandibular vein is uncommon but can be caused by inadvertent laceration of the periosteal envelope.

Early. Early complications include malocclusion, wound infection, hardware failure, periodontal defects (more common with interdental osteotomies), and injury to teeth. Early postoperative neurosensory deficit (inferior alveolar nerve) is not considered a complication, because the majority of cases (more than 85%) demonstrate some degree of paresthesia. Progressive improvement can be observed up to 9 to 12 months postoperatively.

The presence of immediate postoperative malocclusion can be indicative of hardware failure or intersegmental shifting. If this is not detected clinically or radiographically, it is most likely due to proximal (condylar) segment malpositioning during fixation (e.g., if the condyle is not seated in the fossa as it is fixated to the distal segment, upon release of intermaxillary fixation, the condyles reposition, resulting in an anterior open bite).

Infection is a rare complication (less than 3%) in otherwise healthy patients. Hardware removal commonly allows rapid resolution of a draining fistula or ongoing acute infection. Antibiotics may be used to hasten the recovery. Bone fragments that form a sequestrum (frequently a segment of the inferior border) should also be considered in the differential diagnosis of a nonhealing wound.

Late. Permanent neurosensory abnormalities (beyond 12 months) are seen in fewer than 10% of bilateral sagittal split osteotomies. Intraoperative nerve transection, placement of a screw through the nerve, and neurovascular encroachment by bony segments are possible etiologies of permanent nerve injury. Given the high incidence of prolonged postoperative hypoesthesia, the diagnosis of a permanent nerve injury is often very difficult. Due to the spontaneous recovery of the majority of cases, surgeons are generally inclined to observe postoperative hypoesthesia/anesthesia for extended periods. This may lead to permanent neurosensory deficits in a small number of patients who may benefit from early postoperative nerve exploration.

Relapse refers to late postoperative occlusal changes toward the preoperative occlusion. The etiology of relapse is not entirely clear; however, it is hypothesized to be related to postoperative changes in the mandibular bony architecture (e.g., condylar resorption) or to failure of the neuromuscular system to adjust to the new mandibular position, resulting in an unfavorable muscle pull. Relapse is seen in approximately 20% of mandibular advancements and is usually limited to about 15% of the total surgical advancement. It has been shown that larger surgical moves (greater than 7 mm) have a greater possibility of relapse, which supports the neuromuscular adaptation/pull etiology for relapse. Distraction osteogenesis should be considered in patients requiring moves greater than 10 mm.

Discussion

The first description of mandibular osteotomy dates to Hullihen in 1849 (mandibular subapical osteotomy). Subsequently, several techniques and modifications were described, including the Blair ramus osteotomy, Limberg oblique ramus osteotomy, C-osteotomy, inverted L-osteotomy, and vertical ramus osteotomy. The vertical ramus osteotomy is still used by many surgeons via an intraoral approach (intraoral vertical ramus osteotomy). Mandibular orthognathic surgery was revolutionized by the development of the bilateral sagittal split osteotomy by Obegwesser in 1955 in Germany. The procedure has since undergone several modifications by Obegwesser, Dalpont, Hunsuk, and others. Today, the bilateral sagittal split osteotomy remains the most commonly used osteotomy for advancement or setback of the mandible. The Dalpont modification was one of the earlier changes that introduced the vertical cut through the cortex. Hunsuk suggested a shorter medial osteotomy posteriorly, resulting in a shorter split and allowing reduced soft tissue trauma and improved posterior mandibular contour, especially with larger setbacks.

Successful orthognathic surgery requires good communication between the surgeon and orthodontist, in addition to patient commitment to a long treatment period. The main goals of preoperative orthodontic treatment include leveling and aligning the arches, positioning the teeth over the basal bone, and achieving proper inclination of the teeth (dental decompensation), especially the incisors. Placement of molar bands and adequate orthodontic hardware is important for intraoperative maxillomandibular fixation.

Augmentation or reduction genioplasty is frequently used in conjunction with mandibular orthognathic surgery. Similarly, some patients may elect to defer orthognathic surgery and undergo only chin surgery. A patient with mandibular hypoplasia may elect to “camouflage” the abnormality by an advancement genioplasty alone. Although this does not completely address the skeletal issue or alter the dental relationship, it can improve the aesthetic outcome.

The preoperative work-up is a combination of clinical and radiographic planning. The decision for the surgical movements should be predominantly determined from the patient, not the radiographs, in accordance with the adage, “Treat the patient, not the radiograph.” Once the clinical and cephalometric plans are in place, preoperative dental casts should be made and mounted on an articulator with facebow transfer and occlusal registration. The casts should be trimmed anatomically so that measurements and moves on the casts can be accurately transferred to the operating room. Once the model surgery has been performed, based on the cephalometric predictions and clinical examination, the acrylic splint can be made. Measurements should be recorded and verified on the films and surgical casts.

Several adjuncts are used clinically during the operative period to enhance both the surgical field and the patient’s recovery. The use of hypotensive anesthesia at the time of the osteotomy helps to minimize blood loss and increase visibility in the surgical field, allowing for more precise and timely surgery. In general, an increase of up to 500 ml of blood loss can be expected in patients not undergoing hypotensive anesthesia. Although the exact amount of blood loss and increase in visibility are still debated, several studies have shown this method to be effective. A reverse Trendelenburg (head up) position also aids reduction of venous congestion in the head and neck.

The use of antibiotics and steroids has been debated. A single preoperative prophylactic dose of antibiotic is probably useful in reducing the infection risk without undo adverse sequelae. Studies have shown an infection rate of less than 5% with a single preoperative antibiotic dose. Some surgeons suggest continuing antibiotics for 5 to 7 days postoperatively, but this practice is not supported by clinical studies. Continuing antibiotics beyond the preoperative dose is probably unwarranted in an otherwise healthy patient. Corticosteroids have been shown to decrease the total amount and duration of postsurgical edema. They are also beneficial antinausea medications.

Despite the decreases in reimbursement and insurance coverage, orthognathic surgery continues to be a viable tool for the treatment of a variety of clinical diagnoses, and it has a significant impact on both function and cosmesis. The skills required to perform these operations successfully are challenging and require continuing refinement and education.

Bibliography

Baqain, ZH, Hyde, N, Patrikidou, A, et al. Antibiotic prophylaxis for orthognathic surgery: a prospective, randomised clinical trial. Br J Oral Maxillofac Surg. 2004; 42(6):506–510.

Bays, RA. Complications of orthognathic surgery. In: Kaban LB, Perrot DH, Pogrel MA, eds. Complications of oral and maxillofacial surgery. Philadelphia: Saunders, 1997.

Dalpont, G. Retromolar osteotomy for the correction of prognathism. J Oral Surg Anesth Hosp Dent Serv. 1961; 19:42.

Frey, DR, Hatch, JP, Van Sickels, JE, et al. Effects of surgical mandibular advancement and rotation on signs and symptoms of temporomandibular disorder: a 2-year follow-up study. Am J Orthod Dentofacial Orthop. 2008; 133:490.

Gerressen, M, Stockbrink, G, Riediger, D, et al. Skeletal stability following BSSO with and without condylar positioning device. J Oral Maxillofac Surg. 2007; 65:1297.

Hullihen, SP. Case of elongation of the under jaw and distortion of the face and neck, caused by a burn, successfully treated. Am J Dent Sci. 1849; 9:157.

Hunsuk, EE. Modified intraoral sagittal splitting technique for correction of mandibular prognathism. J Oral Surg. 1968; 26:250.

Lee, J. Bilateral sagittal split osteotomy for surgical management of mandibular deficiency. In: Bagheri SC, Bell RB, Khan HA, eds. Current therapy in oral and maxillofacial surgery. St Louis: Saunders, 2011.

Obwegeser, H. The indications for surgical correction of mandibular deformity by the sagittal split technique. Br J Oral Surg. 1962; 1:157.

Praveen, K, Narayanan, V, Muthusekhar, MR, et al. Hypotensive anaesthesia and blood loss in orthognathic surgery: a clinical study. Br J Oral Maxillofac Surg. 2001; 39(2):138–140.

Shepherd, J. Hypotensive anaesthesia and blood loss in orthognathic surgery. Evid Based Dent. 2004; 5(1):16.

Zijderveld, SA, Smeele, LE, Kostense, PJ, et al. Preoperative antibiotic prophylaxis in orthognathic surgery: a randomized, double-blind, and placebo-controlled clinical study. J Oral Maxillofac Surg. 1999; 57(12):1403–1406.

Maxillary Orthognathic Surgery

HPI

The patient admits to some difficulty and discomfort when chewing certain foods, but her main concern is her appearance. She presents to your office after finishing 3 years of orthodontic therapy. She was being monitored for cessation of mandibular growth and possible development of mandibular hyperplasia in conjunction with maxillary hypoplasia. Serial lateral cephalograms at 1-year intervals showed that her mandibular growth was complete (interval superimposition of standard lateral cephalograms is a reliable way to monitor facial growth). Her occlusion has been aligned and leveled for a single-piece Le Fort I osteotomy (if the curve of Spee cannot be leveled in the mandibular arch preoperatively, then postoperative tripod occlusion and postoperative leveling are planned). There is no history or symptoms of temporomandibular joint disorders. (A preexisting TMD should be recognized and addressed before orthognathic surgery, because the latter may exacerbate a preexisting TMD. Although some surgeons recommend simultaneous orthognathic and TMJ surgery in select cases of preexisting anterior disk displacement, this issue is highly controversial.)

Examination

The examination of a patient for orthognathic surgery can be divided into four components: TMJ, skeletal, dental, and soft tissue. Skeletal discrepancies (hypoplasia or hyperplasia) should be assessed in three dimensions: transverse (horizontal), anteroposterior, and vertical. As for all surgical patients, the airway, cardiopulmonary, neurologic, and other organ systems should be assessed in anticipation of the use of general anesthesia.

The maxillofacial examination of the current patient proceeded as follows.

1. TMJ component

2. Skeletal component

 There is no vertical orbital dystopia. The intercanthal distance is 31 mm (normal). The nose is straight and coincident with the midline. Malar eminences are within normal limits.

a. Transverse dimension

b. Anteroposterior dimension

c. Vertical dimension

3. Dental component (occlusion and dentition)

 There is deep bite (Figure 9-6, B).

 Overjet is −6 mm (normal is +3.5 mm ± 2.5 mm).

 Class III relationship is present at the first molars and canines bilaterally.

 Arch width is adequate on handheld models (transverse maxillary deficiencies may require a segmental Le Fort I osteotomy or surgically assisted rapid palatal expansion).

 Curve of Spee has been appropriately leveled, and additional postoperative leveling will be required (1 to 1.5 mm of arch space is required for each 1 mm of curve of Spee leveled).

 Maxillary and mandibular arch forms are ideal.

 Dental compensations have been adequately decompensated without the need for bicuspid extractions (retracting proclined incisors requires 0.8 mm of arch space for each 1 degree retracted; proclining incisors 1.25 degrees gains 1 mm of arch space).

 Dentition is in good repair, with no missing teeth (except for third molars).

4. Soft tissue component

Imaging

The panoramic radiograph and a lateral cephalometric radiograph are the minimum imaging modalities necessary for orthognathic surgery. Preoperative profile, frontal (upon smiling and rest), and occlusal photographs should be obtained. For patients with more complicated conditions, such as facial asymmetry or a cleft, and for those with other syndromes, a PA cephalogram, CT scan, or stereophotogrammetry may be obtained.

For the current patient, the panoramic radiograph shows normal bony architecture of the condylar head and no other pathology. The right and left maxillary and mandibular third molars (teeth #1, #16, #17, and #32) are full bony impacted with minimal root formation.

An initial lateral cephalogram was obtained with the patient in centric relation and lips in a relaxed/reposed position (Figure 9-7). Cephalometric analysis reveals anteroposterior maxillary hypoplasia. This preorthodontic lateral cephalogram illustrates the degree of skeletal discrepancies, in addition to the degree of dental compensations (proclined maxillary incisors); these are important considerations when calculating the adequacy of the existing arch space and determining the need for extractions (decompensating or retroclining flared incisors requires 0.8 mm of arch space for each 1 degree of retraction). It is important to note that measurements differ between Caucasians, Asians, and African Americans (normal values for Caucasian are listed in Table 9-2).

Table 9-2

Cephalometric Analysis

Patient in Figures 9-6 to 9-8 Normal Parameters for Caucasians Patient Notes
Cranial base angle: Normal Sella-nasion (SN)-basion angle: 129 degrees ± 4 degrees
Sella-nasion (SN) to Frankfurt horizontal (FH) angle: 7 degrees ± 4 degrees
 
SNA: 79 degrees 82 degrees ± 3 degrees Patient’s value is suggestive of a maxillary anteroposterior deficiency relative to the cranial base.
SNB: 88 degrees 80 degrees ± 3 degrees Patient’s value is suggestive of an excessive anteroposterior position of the mandible relative to the cranial base.
Harvold difference*: Excessive Females: 27 mm
Males: 29 mm
Patient’s value is suggestive of maxillary hypoplasia or mandibular hyperplasia.
Mandibular plane (MP): Flat SN-MP: 32 degrees ± 10 degrees
FH-MP: 22 degrees ± 6 degrees
 
Long axis of upper incisor to SN angle: 134 degrees 104 degrees ± 4 degrees Patient’s value indicates severely compensated maxillary incisors
Long axis of lower incisor to MP angle: 100 degrees 90 degrees ± 5 degrees  
Upper lip to E-plane: −5 mm −3 mm ± 2 mm  
Lower lip to E-plane: +3 mm −2 mm Patient’s value shows retrusive soft tissue chin and concave profile.

SNA, Sella-nasion, A point; SNB, sella-nasion, B point.

*The Harvold difference is the distance from condylion to pogonion minus the distance from condylion to A point.

Treatment

Treatment of maxillary hypoplasia involves a combined orthodontic and surgical approach for stable results. A coordinated approach involving the orthodontist and the oral and maxillofacial surgeon requires a close working relationship to meet the needs of the patient. The goals of presurgical orthodontic therapy are to:

During the treatment planning phase, the need for dental extractions is determined. The surgeon should be aware of the rationale for arch space management during the presurgical orthodontic phase. It is important to avoid any unstable orthodontic movement (e.g., closing anterior open bites by extruding maxillary or mandibular anterior teeth or widening the posterior maxillary horizontal dimension by tipping the molars) that would later result in relapse. Postsurgical orthodontics is aimed at creating a final, stable occlusion and closing any posterior open bites that resulted from the surgical correction. Frequently, the orthodontist is not able to level the mandibular curve of Spee presurgically and sets up a tripod occlusion. The curve is leveled and spaces are closed postoperatively. Most orthodontists use a retainer for maintenance of the final occlusal relationship and alignment.

Orthognathic surgical treatment options and plans for maxillary hypoplasia are case specific but may include a Le Fort I osteotomy and advancement (single piece versus multiple piece) or bimaxillary surgery. During maxillary advancement, the surgeon can also control the vertical position of the maxilla and incisors, because the mandibular arc of rotation and model setup determine the final position of both the maxilla and mandible (mounted model surgery is paramount to determine the anteroposterior position of the maxillomandibular unit when it is set at the desired vertical position). A Le Fort I osteotomy alone can be considered in the following situations:

A segmental Le Fort I osteotomy is indicated when a transverse deficiency or a dual occlusal plane exists. Bimaxillary (maxillomandibular) surgery (Le Fort I and sagittal split or vertical ramus osteotomies) may be warranted when deformities exist in both the maxilla and mandible, and the mandibular position and arc of rotation cannot be used to position the maxilla (see Maxillomandibular Surgery for Apertognathia later in this chapter). Surgically assisted rapid palatal expansion should be considered when there is a maxillary transverse discrepancy or arch length discrepancy with no other vertical or anteroposterior discrepancies.

Once the surgical treatment plan has been developed, the surgeon can proceed with model surgery to fabricate one or more surgical splints on mounted models. If the open bite is to be closed with maxillary surgery alone, the maxillary cast is set to the ideal occlusion with the opposing mounted mandibular cast (occlusion set with a small posterior open bite maximizes the amount of incisor overlap and reduces relapse). Small posterior open bites can be easily closed orthodontically, especially in young patients (surgically created posterior open bites allow maximal overlap of the anterior teeth, reducing the risk of relapse). A thin interocclusal acrylic wafer (splint) is made to stabilize the occlusion intraoperatively during rigid fixation of the maxilla. If a segmental osteotomy is performed, the splint is made with a palatal strap and wired to the maxillary dentition during the healing phase to prevent horizontal collapse and relapse of the open bite. The maxilla is generally fixated with two-point fixation at the piriform buttress bilaterally using 1.5-mm maxillary orthognathic plates.

For a maxillary osteotomy, the surgeon should discuss with the anesthesiologist the need for hypotensive anesthesia to reduce intraoperative bleeding. When feasible, hypotension induced with β-blockers, rather than “deep anesthesia” produced by anesthetic gases, is preferred, because the former is more effective and easily titrated. After nasotracheal intubation, a local anesthetic with epinephrine is infiltrated into the maxillary buccal vestibule and internal nares (injection of a vasoconstrictor in the palate should be avoided). Incision design is a critical portion of the surgery, and the vascular perfusion of the hard and soft tissues is the most important factor in healing. The most common incision used during Le Fort I osteotomy is a horizontal incision through the mucosa well above the level of the keratinized gingiva (1 cm past the buccal sulcus), from first molar to first molar, made with a scalpel or electrocautery (the parotid papilla should be identified and protected before the incision). The incision is then carried down through the periosteum to bone. Keeping the periosteal incision perpendicular to the bone prevents extrusion of the buccal fat pad. Subperiosteal dissection is performed on the superior aspect of the incision, preserving the cuff of mucogingival tissue. Dissection is carried to the piriform rim, up to the infraorbital foramen, with exposure of the zygomaticomaxillary buttress. Dissection is then carried posteriorly with subperiosteal tunneling to the pterygomaxillary fissure. Attention is then turned to elevation of the nasal mucosa from the medial portion of the lateral wall and floor. After the maxilla has been exposed, vertical reference points can be established (both internal and external references have been used).

A curved retractor is placed at the pterygomaxillary junction, and a Freer or other retractor is placed under the nasal mucosa for protection during the osteotomy. The osteotomy is made using a reciprocating saw, with care taken to remain 5 to 6 mm above the root apices. A nasal septal osteotome is used to free the septal cartilage and vomer from the nasal floor. A spatula osteotome can be used to complete the lateral nasal osteotomies. A pterygoid osteotome is placed and angled slightly inferiorly to avoid inadvertent laceration of the internal maxillary artery, which is approximately 25 mm superior to the pterygomaxillary junction. The pterygomaxillary junction is then separated with the osteotome. Gentle pressure can be applied to the anterior maxilla as the nasal mucosa is elevated. With continuing downfracture, the descending palatine neurovascular bundle comes into view, and care should be taken to prevent injury to the vessels (some surgeons elect to ligate and section the descending palatine neurovascular bundle). Any areas of incomplete osteotomy can be identified and mobilized to completely free the mobilized segment. The maxilla should be completely mobilized so that it can be repositioned and stabilized as planned. If a multiple-piece Le Fort is planned, the interdental osteotomy is made before downfracture of the maxilla, and parasagittal (thinner bone and thicker soft tissue, compared with the midline) osteotomies are made after the downfracture. Also, inferior turbinate reduction should be considered when performing maxillary impactions.

Next, the surgical splint is inserted and secured to the dental arch. The maxillomandibular complex is then passively seated, and any bony interferences are selectively removed until the desired vertical height has been achieved (complete paralysis should be verified with train-of-four twitches by the anesthesiologist). If there are any large defects in the walls of the maxilla, bone grafts can be used. Rigid fixation with plates at the buttress and piriform region is the most commonly used method of stabilizing the maxilla. Once the maxilla has been rigidly fixed, the maxillomandibular fixation can be removed so that the occlusion can be checked. The mandible should seat passively into the splint, verifying proper stabilization as planned. Some surgeons place deep sutures in the muscular layer to reapproximate the facial and labial musculature prior to mucosal closure. The mucosal layer is closed with a running suture in a V-Y pattern to help maintain lip length. Upon completion of the procedure, the occlusion is verified, and light elastics are used as needed to guide the occlusion.

The final results for the current patient are shown in Figure 9-8.

Complications

An important aspect of orthognathic surgery is management of complications. A well-informed patient and attention to detail cannot be overemphasized. The most important complications of maxillary orthognathic surgery are (Box 9-1):

Box 9-1   Most Important Complications of Maxillary Orthognathic Surgery

• Hemorrhage. Intraoperative or postoperative hemorrhage can be life threatening (although rare). Hypotensive anesthesia (mean arterial pressure maintained at around 60 mm Hg) is used by most surgeons to reduce the amount of intraoperative bleeding and to improve visualization of the surgical field. Vascular injury to the pterygoid plexus of veins (most common) can result in a significant amount of blood loss (usually easy to control by packing the wound). An arterial injury (most often the descending palatine artery) is more difficult to control and can result in significant blood loss within a short period (the internal maxillary artery and its terminal branches are most susceptible during the osteotomy and downfracture of the maxilla). Typically, arterial bleeding can be controlled by controlling the blood pressure, proper visualization, pressure/packing, and electrocautery or hemoclips. Uncontrollable arterial hemorrhage warrants emergent angiography and embolization (a carotid cutdown and ligation of the external carotid artery can be performed but is less efficacious due to collateral arterial supply). Turvey and associates have shown that the internal maxillary artery is located 25 mm superior to the most inferior junction of the maxilla and pterygoid plate, leaving a 1-mm margin of safety if a 15-mm wide, curved osteotome is used. Late bleeding (usually preceded by sentinel bleeding) can arise from undetected injury to the descending palatine artery (most common source of postoperative bleeding), pseudoaneurysm formation, or ischemic necrosis of the descending palatine artery due to excessive stretching (especially if the descending palatine artery was not ligated and sectioned during the procedure) and warrants immediate angiography. When required, selective arterial embolization should be cautiously performed to avoid compromising the blood supply to the maxilla. Self-donated blood banking was previously advocated by some groups, but this practice is no longer used (severe bleeding that requires transfusion of packed red blood cells is very rare when appropriate transfusion thresholds are followed). The patient should be informed that intermittent small amounts of dark blood may drain from the nose, which may mimic epistaxis, because the blood collection is emptied from the maxillary sinuses.

• Vascular compromise and maxillary necrosis. Avascular necrosis of the maxilla is the most feared complication after maxillary orthognathic surgery (higher risk for segmental osteotomies and large advancements). The vascular supply to the maxilla arises from branches of the external carotid artery (ascending palatine artery from the facial artery; also, the ascending pharyngeal, greater and lesser palatines, descending palatine, and nasopalatine artery, all from the internal maxillary artery). Some surgeons elect to ligate and section the descending palatine neurovascular bundle, which has been shown to not significantly affect labial gingival perfusion. Vascular insult results from not only the incisions and osteotomies/downfracture, but also from repositioning of the maxilla. If signs of serious hypoperfusion (pale gingival or palatal mucosa with no capillary refill are early signs and mucosal sloughing is a late sign) are noted intraoperatively, the procedure should be aborted and the maxilla positioned and rigidly fixed into its original position. If poor perfusion is observed postoperatively, removal of splints (if wired to the maxilla for postoperative stability) and removal of rigid fixation to allow the maxilla back into its presurgical position may be required. Maxillary splints with a palatal strap should be constructed with caution; if they impinge on the palatal mucosa, vascular compromise can result. Hyperbaric oxygen should be considered postoperatively for maxillary hypoperfusion. Smoking has also been implicated in an increased risk of avascular necrosis.

• Relapse and malpositioning. Long-term stability is one of the main goals of orthognathic surgery. Closing anterior open bites with posterior impaction of the maxilla is more stable than a mandibular osteotomy with surgical counterclockwise rotation of the mandible. However, more recent studies suggest that counterclockwise surgical rotation of the mandible is very stable, especially with the advent of rigid fixation. If anterior open bite occurs in the immediate postoperative period, it is likely due to incomplete seating of the condyles intraoperatively. This can be minimized by inducing complete paralysis during fixation and upward manual pressure at the angles of the mandible when positioning the maxillomandibular unit (the maxilla can pivot around a posterior bony prematurity, which will pull the condyle out of the glenoid fossa during positioning of the maxillomandibular complex). Bays introduced the rigid adjustable pin (RAP) system, which allows for postoperative three-dimensional adjustability. If relapse of the open bite occurs several weeks to months after surgery or release of maxillomandibular fixation, the most common cause is collapse of the horizontal dimension of the posterior maxilla (bony horizontal relapse for segmental Le Fort osteotomies or dental relapse of molars inappropriately tipped laterally). The RAP system can also be used when there is inadequate bone for miniplate fixation. Aggressive mobilization of the maxilla and passive repositioning with rigid internal fixation are also important for improved long-term stability. Widening and downward moves are the most unstable moves in maxillary surgery.

• Neurosensory deficits (greater and lesser palatine, nasopalatine, infraorbital nerves). Although the infraorbital nerve is not severed, traction and compression injuries to this nerve result in a reported 6% incidence of infraorbital nerve neurosensory deficits at 1 year after surgery. Nasopalatine and superior alveolar nerves (posterior, middle, and anterior) are severed during surgery (some surgeons also ligate and section the descending palatine neurovascular bundle). Sensory recovery of the palate is much slower and less complete and is likely due to collateral reinnervation. Neurosensory disturbances of the palate are generally well tolerated.

• Damage to the dentition (maxillary roots) and periodontal defects. This is especially a concern in segmental Le Fort I osteotomies (although there are no studies to suggest a higher incidence of periodontal defects in segmental osteotomies). The majority of these complications can be prevented by careful presurgical orthodontic preparation (diverging the roots at the interdental osteotomy sites) and careful surgical technique.

• Postoperative nasal deformity. Buckling of the cartilaginous nasal septum (quadrangular cartilage) can cause a nasal deformity (deviation of the nasal tip and buckling of the upper lateral cartilages). The nasal septum and the nasal spine of the maxilla and palatine bones should be appropriately trimmed (especially during maxillary impaction), and the caudal portion of the quadrangular cartilage should be trimmed during maxillary advancement. The nasal septum should be secured to the anterior nasal spine with a heavy resorbable suture to prevent displacement during the recovery phase.

Other complications include infection, hardware failure, malunion, fibrous union, and pulpal necrosis (devitalization of the teeth; this is generally prevented if the osteotomy is at least 5 to 6 mm superior to the root apices).

Discussion

The success of maxillary orthognathic surgery is based on the recognition of the blood supply to the maxilla, which was first investigated by Bell. The main blood supply is based on branches of the external carotid system, including the ascending palatine, ascending pharyngeal, palatine, nasopalatine, posterior superior, and infraorbital arteries. With a maxillary osteotomy, it has been shown that the buccal gingival and mucoperiosteal pedicle and the palatal soft tissue pedicle allow preservation of the blood supply and proper wound healing. Proper incision design and minimal dissection of the palatal soft tissues ensure an adequate blood supply.

Traditional methods of stabilizing the maxilla with wires and prolonged periods of maxillomandibular fixation hav/>

Jan 12, 2015 | Posted by in Oral and Maxillofacial Surgery | Comments Off on 9: Orthognathic Surgery
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