Bilateral Sagittal Split Osteotomy

The bilateral sagittal split osteotomy is an indispensable tool in the correction of dentofacial abnormalities. The technique has been in practice since the late 1800s, but did not reach widespread acceptance and use until several modifications were described in the 1960s and 1970s. Those modifications came from a desire to make the procedure safer, more reliable, and more predictable with less relapse. Those goals continue to stimulate innovation in the field today and have helped the procedure evolve to be a very dependable, consistent method of correction of many types of malocclusion. The operative surgeon should be well versed in the history, anatomy, technical aspects, and complications of the bilateral sagittal split osteotomy to fully understand the procedure and to counsel the patient.

Orthognathic surgery involves the surgical correction of the components of the facial skeleton to restore the proper anatomical and functional relationship in patients with dentofacial skeletal abnormalities. An important component of orthognathic surgery is the bilateral sagittal split osteotomy (BSSO), which is the most commonly performed jaw surgery, either with or without upper jaw surgery. Indications for a bilateral sagittal split include horizontal mandibular excess, deficiency, and/or asymmetry. It is the most commonly performed procedure for mandibular advancement and can also be utilized for a mandibular setback of small to moderate magnitude. More than 7 to 8 mm of posterior repositioning of the mandible with a BSSO can be difficult, and consideration should be given to an inverted “L” osteotomy or intraoral vertical ramus osteotomy (IVRO).1Asymmetry cases require careful workup and planning, but can be easily addressed with a BSSO. Cases requiring large advancements, patients with poor soft tissue envelopes, and skeletally immature mandibles are better addressed with mandibular distraction osteogenesis.2 The bilateral sagittal split osteotomy is an indispensable surgical procedure for the correction of mandibular deformities. Undertaking the correction of these deformities requires a thorough knowledge of the indications, technique, and complications of the 

sagittal split osteotomy.

There are several determinants of the optimal modification for BSSO in an individual patient, including the position of the mandibular foramen (lingual), course of the inferior alveolar nerve in the mandible, presence of the mandibular third molars, and planned direction and magnitude of distal segment movement. Although it has been shown that increasing bone-to-bone contact, as in the Dal Pont lateral osteotomy location, should theoretically increase biomechanical stability, in general, however, the location of the lateral osteotomy cut for BSSO varies according to the surgeon's preference and training, and no consensus has been reached regarding the ideal location from the perspective of biomechanics.Although biomechanics is only one of the factors determining the osteotomy technique to be used, it is important for the surgeon to consider the presence of jaw deformities, and their subsequent abnormal forces, while planning the treatment strategy.

The patient is placed in supine position on the operating table with general nasotracheal intubation and is prepared and draped for an intraoral procedure, with the entire face and neck within the field. Bilateral inferior alveolar nerve blocks with a short-acting local anesthetic and vasoconstrictor are given, which can be supplemented by a long-acting anesthetic at the end of the procedure. These blocks are infiltrated into the submucosa anteriorly in the buccal vestibule and along the ascending ramus. Intraoral landmarks are identified for the intraoral incision, including the anterior border of the ramus and the external oblique ridge. A bite block is placed on the contralateral side, and a Minnesota retractor is placed lateral to the external oblique ridge, to expose the mucosa overlying the anterior border of the ramus. A point is identified at just above halfway up the anterior border of the ramus, and the mucosa is incised with electrocautery continuing inferiorly, lateral to the external oblique ridge, to the second molar, where the incision continues more laterally into the vestibule down to the distal first molar. A cuff of tissue should be preserved medial to the incision to facilitate closure. The incision is continued through submucosa, muscle, and periosteum with electrocautery. With a periosteal elevator, the periosteum is elevated, exposing the external oblique ridge up to the coronoid notch. A periosteal elevator is used to dissect all of the tissue along the buccal surface of the ramus and the proximal mandibular body. Dissection is carried down to the inferior border of the mandibular body and the posterior border of the ramus. A J-stripper is then inserted along the inferior border of the mandible and all attachments are released. A V-shaper retractor is then placed along the external oblique ridge and all attachments to the anterior ramus are released as superior onto the coronoid as possible. A Kocher clamp with a chain is then placed on the coronoid process and secured to the surgical drape. Subperiosteal dissection continues along the internal oblique ridge inferior to the level of the occlusal plane to allow visualization of the medial aspect of the ramus. Starting superiorly a blunt elevator is passed posteriorly and inferiorly until just superior and posterior to the lingula.

Once all of the soft tissue dissection has been completed, attention can be turned to the osteotomies. A small elevator is placed along the medial aspect of the ramus and is utilized to retract and protect the pedicle. The lingula is typically located 1 cm above the occlusal plane and between one-half to two-thirds the distance from anterior to posterior on the ramus. Once the pedicle is adequately protected, a channel retractor is inserted to provide lateral retraction, a Kocher is placed to provide superior retraction, and a reciprocating saw is placed medial to the ascending ramus, superior to the lingula and parallel to the occlusal plane. The cut is made through the cortical bone and into the cancellous bone, and then the saw is turned and the cut continued anteriorly down the external oblique ridge to the level of the second molar. Depending on each surgeon's training and preference, this cut can be made with the reciprocating saw or with a fissure bur. The final cut is then made vertically along the buccal cortex at the level of the second molar down to the inferior border of the mandible. It is important that this cut is made completely through the cortical bone along the inferior border. All of the cuts are then checked to ensure that they are complete through the cortex and down to cancellous bone. The osteotomy is then finished with small curved osteotomes, taking care to direct the curve buccally and to protect the soft tissues with a channel retractor. The osteotomes progress from anterior to posterior completing the cut. It is important to make sure that each one is complete down to the channel retractor below and that no twisting forces are utilized to prevent a bad split. As the split is opening, check the position of the inferior alveolar nerve, if it is hung up either on the lateral or proximal segment, use a blunt elevator to gently release it. Once the osteotomy is complete, check that each segment is free of the other and that the condylar head is still attached to the proximal segment.

Now the mandible is placed in its desired position with the aid of the prefabricated splint and any intervening bone is removed if performing a mandibular setback. The two segments are then fixated according to the surgeon's preference with either three bicortical screws on either side or with a miniplate with three holes on either side of the osteotomy. Care is taken during the placement of fixation to ensure that the condyle remains within the fossa and that the inferior border is well aligned. Once the segments are fixated, check the occlusion to ensure that it is satisfactory. If the desired occlusion has been reached, the incisions are closed with absorbable suture following copious irrigation and hemostasis. Guiding elastics can be placed intraoperatively or postoperatively following extubation.