Inverted L osteotomy

The inverted L-osteotomies are full thickness osteotomies of the rami. If performed bilaterally they divide the mandible into two segments that contain the condyle, posterior border and coronoid process and a large segment consisting of the mandibular body including the teeth and chin.

The osteotomies are performed posterior and superior to the inferior alveolar canal.

The osteotomy is usually performed using a submandibular approach, especially for difficult movements and those requiring bone grafting (asymmetric craniofacial deformities, such as Hemifacial microsomia).

Alternatively the procedure can also be performed using a transoral approach for some simple movements.

This is a procedure that can be employed for:

• posterior repositioning,
• mandibular rotations
• shortening and lengthening of the posterior ramus
• large mandibular advancements (with bone grafting)

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

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

The sagittal anterior cut for an inverted L-osteotomy can easily be performed from a transoral route.

It is a full thickness osteotomy, usually done with a reciprocating saw, which stops 8-10 mm anterior to the posterior border of the mandible, but posterior to the inferior alveolar canal.

The vertical component requires the use of an angulated oscillating saw or piezoelectric instrument when performed from a transoral approach.

When using a submandibular approach, a reciprocating saw can be used for the vertical osteotomies and an oscillating saw can be used for the horizontal osteotomy.

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

For mandibular setbacks the proximal segment will rest lateral to the repositioned distal segment.

For large anterior and inferior movements, a gap will result between the proximal and distal segments necessitating the need for bone grafting.

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.

Internal fixation is always necessary with an inverted L-osteotomy to prevent the temporalis muscle from rotating the proximal segment superiorly.

Internal fixation is difficult to perform through a transoral approach because of problems with access. It is easier if an external approach is used and then can be performed using miniplates and monocortical screws.

Bone plate or bicortical screw osteosynthesis can also be performed using transbuccal trochar instrumentation.

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.