BSSO (Obwegeser)

The Obwegeser osteotomy is a bilateral sagittal split osteotomy of the ramus, which divides the mandible into two smaller condyle bearing segments and a large segment consisting of the mandibular body including the teeth and chin

This is a universal procedure that can be employed for all mandibular movements.

To illustrate the procedure, we will here show the correction of mandibular prognathism.

The obvious problem of this procedure is the close proximity of the osteotomy lines and the neurovascular canal. Care should be taken not to damage the inferior alveolar nerve during this procedure.

For a detailed description of how to plan orthognathic surgery, please click here.

For this procedure the transoral approach to the mandibular angle is used.

The procedure starts with three corticotomies.

The first cut is made through the lingual cortex a few mm above the mandibular foramen parallel to the occlusion. The corticotomy is extended from the anterior to the posterior borders of the ramus.

The second corticotomy is made through the buccal cortex, again parallel to the occlusion at the level of the alveolar crest. The corticotomy is extended from the anterior to the posterior borders of the ramus.

The third corticotomy connects the first two osteotomy lines along the anterior border of the ascending ramus.

The final split is completed with a thin osteotome, splitting the entire ascending ramus from the anterior to the posterior border of the ramus.

A special bone spreader can be used to mobilize the segments.

After the bilateral split is completed the large tooth bearing segment can be moved three dimensionally.

Some movements, such as superior positioning of the tooth bearing segment, will require removal of bone to allow for a good alignment of the respective segments.

Mandibulo-maxillary fixation is performed to position the tooth bearing segment to the desired relationship with the maxilla. A prefabricated surgical splint (or wafer) may be used to facilitate this.

Care must be taken to maintain the normal fossa-condyle relation (see upper insert) and to avoid condylar displacement (see lower insert). Usually this is achieved by manual positioning of the condyle bearing segment superiorly into the glenoid fossa.

An alternate method of positioning the condyle bearing segment is to use a condyle positioning device.

After outlining the osteotomy lines, the patient is placed into MMF using a centric relation bite wafer. Plates are adapted to span between the ascending ramus and the maxilla or zygomatic bone bilaterally, taking care to avoid the planned osteotomy sites.

Positioning plates and MMF are then removed and the bilateral sagittal split osteotomy is performed.

After placing the patient into the desired final occlusion, the positioning plates are re-attached to position the condyles into their preoperative position within the glenoid fossa. An alternative to this is intraoperative position control with navigation.

Finally the osteosynthesis is performed and the condylar positioning device removed.

Some movements, such as superior positioning of the tooth bearing segment, will require removal of bone to allow for a good alignment of the respective segments.

Internal fixation is usually performed with positioning screws, plates or combinations. Screw placement is usually performed with either transbuccal instrumentation or angulated drills and screwdrivers.

Bone supported devices

A minimum of two and preferably three bicortical position screws are placed between the buccal and lingual cortices.

Care should be taken to avoid damaging the inferior alveolar nerve.

Two possible patterns of screw placement are demonstrated.

A plate can be applied across the segments on the lateral aspect of the mandible using monocortical screws. A minimum of two screws on each side of the osteotomy is necessary.

Avoid placing the plate and screws in close proximity to the alveolar canal in order to avoid damage to the inferior alveolar nerve.

Combinations of a single plate and a positioning screw (anti rotation screw) are also possible. This improves stability against rotational forces.

After completion of osteosynthesis on both sides, the MMF is released and the resulting occlusion is checked against the pre-planned position. The splint may be fixed to the maxillary teeth with a few thin wires and left in place during the healing phase to allow for neuromuscular adaption and position control.

If MMF screws or Temporary Anchoring Devices (TADs) are used intraoperatively, they are removed at the end of surgery if not further needed for elastic traction. If a final splint was used, it may be fixed to the orthodontic devices (brackets) of the upper jaw to assure the planned occlusion and to serve as guidance for the neuromuscular adaption during functional training for about 2 weeks postoperatively.

To reduce swelling, the application of ice-packs or cooling devices during the early post-operative phase is advice. Intravenous steroids should also be continued for a short period postoperatively for the same purpose.

Antibiotic prophylaxis is continued for 1-5 days depending on the nature, complexity, and duration of the surgical procedure.

Especially in two-jaw surgery, the airway control is of major importance. An individual decision has to be taken if the patient can be extubated or should remain intubated until it is clear that safe airway can be established.

Early post-operative x-rays are obtained to verify correct segment position. Additional postoperative imaging is performed as needed.

Regular follow up examinations to monitor healing and the postoperative occlusion are required. If an occlusal problem is present in the early postoperative phase, the surgeon must determine its etiology. If the malocclusion is secondary to surgical edema or muscle detachment/disorders, training elastics may be beneficial. The elastics are only used for guidance, because active motion of the mandible is desirable. Patients should be instructed how to place and remove the elastics using a hand mirror. If the malocclusion is secondary to a bone problem due to inadequate fragment positioning, displaced or failed hardware, or condylar displacement during surgery, elastic training will be of no benefit. The patient must be rescheduled for revision surgery.

At each appointment, the surgeon must evaluate the patient's ability to perform adequate oral hygiene and wound care and should provide additional instructions if necessary.

Postoperatively, patients will have to follow three basic instructions:

1. Diet
In orthognathic surgery the internal fixation devices usually do not allow for full functional load. A soft diet should be used up to 6 weeks, starting with liquids for the first 3-4 days. Elastics can be removed during eating.

2. Oral hygiene
Patients with intraoral wounds must be instructed in appropriate oral hygiene procedures. The presence of orthodontic appliances, the splint, and elastics makes this a more difficult task. A small soft toothbrush with toothpaste should be used.Any elastics are usually removed for oral hygiene procedures. Additionally, antiseptic rinses can be used in the early postoperative period. An oral irrigator (eg, Waterpik) is a very useful tool to help . If a Waterpik is used, care should be taken not to direct the jet stream directly over intraoral incisions to prevent wound dehiscence in the early postoperative phase.

3. Functional training/physiotherapy
The patient is instructed how to perform functional training (opening and excursive exercises) as soon as possible. The progress should be monitored by the surgeon. If available and needed, a physiotherapist can support the functional rehabilitation. An undisturbed mouth opening of minimum 35 mm interincisal jaw opening should be attained by 4 weeks postoperatively.

In case of undisturbed healing, the postoperative orthodontic treatment can usually start 2 to 6 weeks after surgery depending on the case.