1 Principles topenlarge
Biomechanics of the symphysis
The mandibular symphysis undergoes torsional forces (twisting) during function. Therefore, fixation strategies must take this into account. When using anything less stable than a reconstruction plate, two points of fixation should be applied.
In general, the further apart the points of fixation, the more stable the construct. For symphysis fractures, when two plates are applied, they should be separated as much as possible without injuring vital structures.
Illustration shows Champy’s ideal lines of osteosynthesis for symphysis fractures.
Following special considerations may need to be taken into account:
- Multiple fractures
- Edentulous atrophic fractures
- Teeth in the line of fractures
- Involvement of alveolar area
- Infected fracture with or without bone loss
Click on any subject for further detail.
2 Choice of implant topenlarge
The choice of implant is according to surgeon preference. Simple (linear) fractures with no associated injuries can easily be treated with miniplates. However, there are often associated injuries in the mandible and the surgeon may elect to use more rigid fixation. Locking plates with different profiles offer increased rigidity and still can be placed using the same surgical approach.
3 Reduction topenlarge
Predrilling monocortical holes
It is necessary to predrill two monocortical holes below the apices of the teeth on either side of the fracture to help place the reduction forceps.
Manipulate the mandible fragments until anatomic reduction is achieved. Apply the reduction forceps and then place the patient into occlusion and secure with MMF.
Some surgeons prefer to place the patient into occlusion and apply MMF before using the reduction forceps.
The clamp has to be placed perpendicular to the line of fracture to prevent fracture displacement when tightening the reduction clamp.
4 Fixation topenlarge
In general, a minimum of two points of fixation should be used to provide stable internal fixation of mandibular symphysis fractures.
Because the mandibular symphysis undergoes twisting during function, two miniplates can prevent such motion from occurring.
Apply the first plate to the inferior border of the mandible.
Contour the plate using bending pliers.
Position the plate a few millimeters superior to the inferior border. Because miniplate fixation is adaptation osteosynthesis and does not compress the fracture, the plate can be placed in a direction other than perpendicular to the fracture line.
Drill first screw hole
Use a 1.5 mm drill bit with 6 mm stop to drill monocortically through the plate hole next to the fracture.
Insert a 2.0 mm screw, 6 mm in length. Do not fully tighten it until the final reduction and plate position are confirmed.
Insert second screw
Insert a second screw on the other side of the fracture in the same way.
Tighten both screws.
Additional screw placement
Fill the remaining plate holes with screws.
Application of second plate
Remove the reduction forceps.
Now place a second miniplate 2.0 below the apices of the tooth roots.
Occasionally, the plate must be positioned higher on the mandible. Great care must be taken when drilling in this area as tooth roots can be just below the cortex and can be damaged using a 6 mm drill bit with stop.
Confirmation of reduction
Confirm adequate reduction. There must be no gap at the lingual aspect. Such a gap would lead to occlusal disturbance and mandibular widening.
MMF is released and the occlusion checked.
Because two points of fixation have been applied (two miniplates), it is not essential that the arch bars remain in position.
5 Case example topenlarge
Routine diagnosis of this type of fracture should include x-rays taken in two planes at 90° to each other; the minimum requirement is a PA view and a panoramic view.
CT scan or digital volume tomography (DVT) imaging may be used as an alternative.
Note that in this symphyseal fracture, the fracture begins between the central incisors and extends posteriorly as it approaches the inferior border.
X-ray shows the completed osteosynthesis.
Clinical view shows fracture fixation with two mandibular miniplates 2.0.