 Today let's discuss about bilateral sagittal split osteotomy or BSSO also known as bilateral split haremous osteotomy or simply sagittal split osteotomy. Sagittal split is a versatile technique which enables movement of mandible in the anteroposterior direction. Let's see how this highly flexible technique has evolved over time. Though the technique was first described by Schuessart in 1942, it was popularized by Obwigiser in the year 1955. Dalpont has given a major modification to the procedure by extending the oblique cut to the second molar region. Hansen modified the medial cut by extending it just behind the mandibular ferramen. Epker later extended the vertical cut up till the inferior border of mandible. So this is how the technique of sagittal split has evolved over time. What are the indications of sagittal split? This technique can be used to treat both the retrognathism and prognathism of mandible. Horizontal mandibular axis, horizontal mandibular deficiency and mandibular asymmetry are few indications of sagittal split. If the mandibular advancement is to exceed 10 to 12 mm, then an extra oral approach has to be considered. Whereas if the mandibular sit back exceeds 7 to 8 mm, then intraoral vertical ramus osteotomy or an inverted L osteotomy is considered, not a sagittal split. Before moving on to the technique, let's have a quick look at the anatomy relevant to sagittal split osteotomy. This is the medial view of mandible where you can see the mandibular ferramen. It is through this mandibular ferramen that the inferior alveolar nerve enters into the inferior alveolar nerve canal. At the opening of the ferramen, there is a tongue like bony projection known as lingula. The first medial osteotomy cut is performed just superior to the lingula extending just behind the ferramen. In this lateral view of mandible, you can see the ascending ramus and the external oblique ridge. The second osteotomy cut of sagittal split is performed through this external oblique ridge extending up to the second molar or the first molar. The third vertical osteotomy cut connects the oblique cut to the inferior border of mandible. So for a better understanding of the procedure, keep this picture in your mind. Let's now move on to the technique of sagittal split. The procedure is usually done under general anesthesia with the patient in supine position. The leg solution is infiltrated into the buccal vestibule along the ramus on both the sides. The landmarks those need to be kept in mind are the anterior border of ramus, the external oblique ridge, lingula and mandibular ferramen. Coming to the incision. The incision begins at the middle of anterior ramus. This is the ascending ramus and this is approximately the mid ramus. From the middle of the ramus, the incision is extended inferiorly along the external oblique ridge towards the first molar and it then curves down to the buccal vestibule. This is the path followed by incision. Initially only the mucosa is incised. You need to retract the tissues buckly before deepening the incision to prevent any infiltration of the buccal pad of fat into the surgical site. So this is to be remembered that the tissues on the buccal side has to be retracted before deepening the incision. The incision is then cut through the submucosa, muscle and periosteum. So once the incision is completed, periosteum is elevated using a periosteal elevator. The tissues on all the three sides has to be retracted. Superiorly the tissues are retracted to expose till the tip of the coronoid. The tip has to be visible after retraction. Then retract laterally till the inferior border of the mandible. On the lateral side, you reflect the tissues till you see the inferior border of the mandible. And on the medial side, expose the internal oblique ridge and up till the superior and posterior portion of the lingula. On the medial side, you need to expose the internal oblique ridge and the superior portion as well as posterior region of lingula. Also you need to relieve the temporalis fibers from the medial side of coronoid. As you know the fibers of temporalis muscle gets attached to the tip of the coronoid. Therefore, it is necessary to relieve the fibers from here. So once the soft tissue dissection is over, you proceed with the bone osteotomies. So before we describe each osteotomy in detail, let's have a look at what are the different osteotomies used in sagittal split. There are three osteotomy cuts used in a sagittal split. The first one is a medial horizontal cut. The medial horizontal osteotomy is performed on the medial aspect of the mandible. Then the second cut is a oblique one. It is an oblique one and it is an intermediate one. So it extends from the medial cut down towards the external oblique ridge towards the molar region. This is the intermediate oblique osteotomy. The third osteotomy is a vertical buckle cortical osteotomy which is performed from the lower border of the mandible and it connects to the oblique cut. So there are three osteotomies, basically a medial horizontal osteotomy, an intermediate oblique osteotomy and a vertical buckle cortical osteotomy. Now let's see each of these osteotomies in detail. The medial horizontal osteotomy is performed first using a reciprocating saw or a burr which is inclined at an angle of 45 degrees to the bone surface. The bone cut should extend superior to and posterior to the lingula that is about two-third the anterior posterior dimension of the ramus which should be kept in mind that the bone cut should extend into the medullary bone and not just remain within the cortical bone. Also, the cut should be made in such a way that it is parallel to the occlusion plane. The intermediate oblique osteotomy is an extension of the medial horizontal cut. This osteotomy is taken downward through the external oblique ridge towards the second molar region. This intermediate oblique osteotomy should be parallel to the lateral contour of the mandible. Remember that this bone cut should be parallel to the lateral surface of the mandible. The oblique osteotomy can also be extended towards first molar region just for better accessibility. Prior to performing the vertical buccal cortical osteotomy, protect the soft tissues at the lateral and inferior border of the mandible using a channel retractor. The vertical osteotomy should involve the lower border of the mandible. The vertical cut starts from the inferior border of the mandible. It goes up straight perpendicular to the occlusion plane. It goes for about 2 cm before joining the oblique cut. So hence all the three osteotomies are completed. The first osteotomy cut is the medial horizontal osteotomy, the second one is the intermediate oblique and the third one is the vertical buccal cortical osteotomy. Once you have performed all the three osteotomies, it is now time to complete the sagittal split. A small spatula osteotome is used to mallet from the medial to the vertical cut. That means the osteotome is used beginning from the medial horizontal cut along the oblique intermediate osteotomy and then finally to the vertical cut. Make sure that the osteotome is directed lactally towards the lateral side of the mandible and not towards the medial side. Also be careful not to damage the neurovascular bundle. Once the osteotome is used to mallet from the medial cut to the vertical, then use a smith spreader to complete the sagittal split in a prying motion. The smith spreader is used in a prying motion to complete the sagittal split. Any incomplete trying or any incomplete split can lead to adverse fracture. So keep in mind that the prying should be complete and the split also should be complete. It is important to visualize the neurovascular bundle throughout the procedure while performing a sagittal split visualize the neurovascular bundle and always maintain it in the medial or the proximal segment. What is the medial segment? The segment that contains the condylar head is known as the medial segment and the segment that bears the teeth is the distal segment. So keep in mind the one that bears the condyle is the proximal segment and the one bearing the teeth are the teeth is the distal segment. In case the nerve bundle is embedded within the bone, in the proximal segment if it is embedded within the bone it is important to relieve it. It is important to relieve it from between the bone irregularities otherwise this can lead to a nerve injury or temporary nerve damage later on. In case of advancement, in case you are advancing the mandible, separate the medial tergoid muscle from the inferior border of the distal segment. As you know the medial tergoid gets attached to the middle aspect of the mandible. So if you are advancing the mandible make sure that the medial tergoid attachment is relieved from the distal segment because we don't want any stretching of the muscle as you advance the mandible forward. In case you are doing a mandible as a setback, again you need to strip off a certain amount of the tergo masatric sling. So here make sure the stripping is minimal. If the stripping is excessive there are chances that the segment will not survive and there will be necromancy. After the split is complete and the neurovascular bundle is preserved the mandible is then advanced or setback as required. It is a distal segment that is advanced forward or which is setback. In a setback the desired amount of cortical bone is removed from the distal segment. That means a desired amount of cortical bone is removed from here this aspect of the distal segment. Why is it done? So that it doesn't override with the proximal segment. When you take the distal segment behind it should not override with the proximal segment. For that reason a small amount or the desired amount of cortical bone is removed. And it is also done so that both the segments both the proximal and the distal segments maintain a cancerous bone contact. When a small portion of cortical bone is removed then it is the cancerous bone which comes in contact and this will enhance healing. So this is how the mandible is brought forward or behind following a sagittal split. Once the mandible is repositioned occlusion needs to be checked and confirmed. Then the maxillum mandibular complex is placed in an IMF. And like in any other osteotomy in sagittal split also the bony segments are fixed using either a rigid internal fixation, bone plates, a large bone plate in case of advancements or lag screws or wiring. If bone wiring is used then IMF needs to be maintained for another five to six weeks. This is how the distal and the proximal segments are stabilized and fixed. Postoperative complications like edema, diminished sensation of lips and limited jaw movements are often experienced by the patients. Few other complications include a wrong split. When a third molar is removed during the time of surgery there are chances that the sagittal split can turn into an unfavorable fracture. So it is advised to have the third molar removed at least six months prior to the surgery. Also neurosensory deficit has been observed among patients who have undergone a bisagittal split. So if a nerve is cut or transplanted during the surgery it is advised to perform a microanastomosis. Also care has to be taken while plating both the distal and proximal segments because an improper plating can either push or pull the contact into an untoward position and this can lead to TMJ problems and relapse later on. Another complication is excessive bleeding. It can be from inferior alveolar neurovascular bundle or medullary bed or even from facial vessels. So if the bleeding is from an inferior alveolar neurovascular bundle or if it is a bone bleed it can be controlled using local hemostatic measures. If the bleed is from facial vessels then the vessels have to be clamped and tied which can be done only through an incision performed extra overly. So these are the complications with sagittal split osteotomy and this is all about bilateral sagittal split osteotomy. Thank you.