CC
A 22-year-old female is referred by her orthodontist for evaluation and surgical treatment of an asymmetric class III skeletal malocclusion. The patient reports “My lower jaw is crooked.”
HPI
This patient previously underwent comprehensive orthodontics at a younger age. However, as she aged, she noticed her occlusion began to change. She was reevaluated by her orthodontist several years later and subsequently referred to her oral surgeon for surgical correction of her skeletal malocclusion. She denies any temporomandibular joint (TMJ) dysfunction symptoms.
PMHX/PSHX/medications/allergies/SH/FH
Noncontributory.
Examination
The patient’s preoperative clinical photos can be appreciated in Fig. 60.1 . Her examination, as outlined as follows, was divided into four components, TMJ, skeletal analysis, dental analysis, and soft tissue analysis.
- 1.
TMJ
- a.
Full range of motion
- b.
No significant deviation
- c.
No pain, clicking, popping, or crepitus
- d.
Maximal incisal opening of approximately 40 mm
- a.
- 2.
Skeletal analysis
- a.
Lower facial third with deviation to the left of midline
- b.
Transverse
- i.
Maxillary midline is coincident with the facial midline.
- ii.
The chin point is about 4 mm to the left of the facial midline.
- iii.
There is no maxillary cant.
- iv.
The arch lengths of the maxilla and mandible are coordinated (because of previous orthodontic therapy).
- v.
The mandibular midline is 4 mm to the left of midline.
- i.
- c.
Anteroposterior dimension
- i.
Nasolabial angle: 97 degrees
- ii.
Labiomental angle: 127 degrees
- iii.
Straight facial profile
- i.
- a.
- 3.
Dental analysis
- a.
Class III at both the first molars and canines
- b.
Overjet is 0 mm; overbite is 0%; edge-to-edge occlusion
- c.
Posterior crossbite on the left side
- d.
Level arch form, well aligned, and without crowding
- a.
- 4.
Soft tissue analysis
- a.
Normal overlying soft tissue envelope
- b.
Adequate thickness of the upper and lower lips
- c.
No labial incompetence or mentalis strain
- a.
Imaging
In mandibular orthognathic surgery, proper imaging remains crucial to achieving successful results. The panoramic radiograph and lateral cephalogram continue to be the standard for treatment planning orthognathic surgery. The advent of modern imaging techniques, including traditional and cone-beam computed tomography (CBCT) scans, has expanded surgeons’ ability to plan orthognathic surgeries virtually.
The panoramic radiograph allows the surgeon to critically evaluate the patient’s dentition as well as the maxilla and mandible in one image. Additionally, it displays the position and development of the patient’s third molars if present. Removal of third molars before or at the time of mandibular orthognathic surgery is a debated topic among oral and maxillofacial surgeons. There is conflicting evidence in the literature regarding whether removing third molars before mandibular orthognathic surgery is beneficial in reducing intra- and postoperative complications. However, the patient’s age appears to be associated more with unfavorable splits than the presence of third molars. Fig. 60.2 A demonstrates the patient’s preoperative panoramic radiograph.
A lateral cephalogram is an excellent tool for evaluating the patient’s skeletal positioning in the anteroposterior dimension. This image allows the practitioner to perform cephalometric analysis before surgery and is the standard in preoperative imaging for mandibular orthognathic surgeries. Most important, this image provides information on how the mandible relates to the maxilla and skull base, aiding in diagnosis and treatment planning. Fig. 60.2 B demonstrates the patient’s preoperative lateral cephalogram. Currently, most cephalometric analyses are completed via a digital workflow by manually selecting the necessary landmarks within an analytical software. Recent advances in software engineering have been made toward automatic tracing and analysis via artificial intelligence with high degrees of sensitivity and specificity. However, this technology has yet to be widely implemented, and further study is warranted.
Recent advances in digital imaging have improved the preoperative treatment planning for patients undergoing orthognathic surgery. Traditional and CBCT scans have been implemented to improve surgical outcomes. CT imaging modalities allow virtual three-dimensional reconstructions and enhanced soft tissue analysis during preoperative planning. Although CBCT scans are more widely available in most oral surgery offices, many still need to provide adequate fields of view for the digital workflow of virtual surgical planning. Although not necessary for all orthognathic cases, CT imaging is a valuable tool for navigating complex dentofacial deformities and asymmetries.
Treatment
Orthognathic surgery may treat various dentofacial conditions, including deficits in speech, difficulty swallowing, problems with mastication, TMJ disorders, or obstructive sleep apnea. Aesthetic concerns also drive orthognathic surgery. Mandibular orthognathic surgery is mainly dependent on any coexisting maxillary deformity. If none exists, one may proceed with mandibular surgery alone. However, bimaxillary surgery may be indicated with coexisting deformities because the maxillary occlusal position establishes the final position of the mandible.
The sagittal split osteotomy (SSO) is the culmination of several modifications, resulting in a safe and reliable way to treat multiple deformities in the mandible. The procedure’s versatility allows it to set back or advance the mandible or correct asymmetries within the dentofacial complex. Other mandibular osteotomies can be used for mandibular orthognathic surgery, such as the intraoral vertical ramus osteotomy, inverted L osteotomy, or a combination of the various osteotomies. Various factors are considered when deciding which osteotomy should be performed. Some things to consider are the anticipated movement of the distal segment, the patient’s preexisting TMJ disorder, concern for neurosensory deficits, ability to tolerate maxillomandibular fixation, and concern for a cervical incision. For the sake of the discussion, and the decision that was made for the patient described, we will continue with describing the SSO.
The patient is brought to the operating room and nasally intubated with a nasal RAE tube. Bilateral inferior alveolar nerve blocks are given using a 50:50 mix of 1% lidocaine with 1:100,000 epinephrine and 0.5% Marcaine with 1:200,000 epinephrine. An oropharyngeal screen and bite block were placed in the patient’s mouth. The external oblique ridge is palpated with a Minnesota retractor, and an incision is made just over the ridge using Bovie electrocautery, being careful to leave a 5-mm cuff of attached gingiva. A #9 periosteal elevator is then used to dissect in a subperiosteal plan on the medial and lateral aspect of the mandible, as well as superiorly to the coronoid. It can be helpful to use the Bovie electrocautery to remove some of the temporalis tendon while a V-notch retractor is placed on the coronoid and pulled superiorly.
When the dissection is performed on the medial aspect of the mandible, it is best to start farther posterior than the anticipated location of the lingula. After a subperiosteal dissection is established, a #9 periosteal elevator can be used to palpate the stop of the lingula. This is then confirmed with placement of a nerve hook in the lingula.
After the dissection is completed, it is important to evaluate the anatomy of the patient’s ramus. Although a gentle S curve is often pictured in diagrams for the SSO, if the patient has a narrow ramus, there may not be adequate room for a curve from the medial to sagittal components of the osteotomy. If the ramus proves to be narrow, it is likely the medial osteotomy will need to be angled so that it directs straight into the sagittal osteotomy. The authors find it helpful when discussing the anticipated osteotomy with residents to mark the mandible with a sterile pencil because the marking is not easily removed by blood or irrigation.
Before the medial osteotomy is made, a periosteal elevator is placed on the distal aspect of the lingula to protect the neurovascular bundle. If desired, a lighted medial ramus retractor can be placed over the periosteal elevator, which is then removed to allow for additional light, visualization, and protection of the neurovascular bundle. It is the authors’ preference to use a reciprocating saw to perform the osteotomy. First, a medial osteotomy is made at the level just above the lingula, at a 45-degree angle, if possible. It is important to ensure the osteotomy extends beyond the lingula posteriorly.
Then the osteotomy is continued in the sagittal plane, taking care to ensure the saw is cutting through the outer cortex and just into medullary bone. The sagittal component extends anteriorly to the area of the second molar. The reciprocating saw should parallel the orientation lateral ramus and mandibular body. Additional thought needs to be considered when determining how far anterior the sagittal osteotomy should extend. If there is a significant advancement anticipated, it is useful to extend the osteotomy further so there will be adequate bony contact after the advancement is complete.
Before the lateral osteotomy is made, the bite block is removed, and pressure is placed on the mandible to occlude the teeth, which allows for easier access for the lateral and inferior border osteotomies. First, the lateral osteotomy is made at the anterior extent of the sagittal osteotomy. Attempts are made to make this a gentle curve connecting the sagittal and lateral osteotomies. The lateral osteotomy should be at a 45-degree angle. Next, the inferior border is cut approximately 2 mm.
After the osteotomies have been completed on both sides, the mandible is split using a mallet and small, straight osteotomes. Beginning with the medial osteotomy, a small osteotome is propagated to ensure the osteotomy extends past the lingula. Then, progressively moving anterior, an osteotome is tapped with the mallet the entire distance of the osteotomy. If movement of the segments is not appreciated, the surgeon should localize where there may be a need to refine the osteotomy with the reciprocating saw. When slight movement is appreciated throughout the osteotomy, a large osteotome can be placed at the most anterior aspect and at the inferior border, and a Smith spreader is placed more posterior, to begin slowly propagating the split. Again, attention is needed during this time to visualize the osteotomy moves as anticipated. After the split is complete, the inferior alveolar nerve is visualized and confirmed to be in the proximal segment. After completing both sides, the proximal segment may be mobilized and placed into the proper occlusal position using a prefabricated splint, and maxillomandibular fixation is applied. A pickle fork is used to apply gentle pressure on the proximal segment to seat the condyle in the glenoid fossa. The osteotomy site is checked for any interferences that need to be removed, and the inferior borders of the proximal and distal segments are aligned. The surgical sites are then fixated with plates. Maxillomandibular fixation is removed, and the occlusion is confirmed to be as planned.
The patient remained for observation postoperatively and was discharged on postoperative day 1. She continued to follow up in the clinic. Postoperative clinical photos and imaging can be appreciated in Fig. 60.3 .
