1 Principles topenlarge
Biomechanics of the symphysis
The mandibular symphysis undergoes rotational 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 one plate is applied along with a stable arch bar, the plate should be placed as close as possible to the inferior border of the mandible.
This technique requires a stable arch bar be placed across the fracture line. For those cases where there is a tooth missing in the line of fracture or the teeth are loose, an arch bar is not recommended to provide the second point of fixation. Thus, a second point of fixation on the bone must be provided.
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
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2 Reduction topenlarge
Drilling monocortical holes
It is necessary to pre-drill two monocortical holes below the apices of the teeth on either side of the fracture to help when placing the reduction forceps.
Manipulate the mandible fragments until anatomic reduction is achieved, apply the reduction forceps and then place patient into occlusion and secure it 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.
3 Fixation topenlarge
Choice of implant
An ideal choice is a large, thick and wide plate type such as the large profile locking plate 2.0, dynamic compression plates (DCP) or universal fracture plates (UFP).
The minimum size for the plate at the lower border of the mandible is a mandible plate 2.0 or a small profile locking plate 2.0.
Contour the plate using bending pliers.
Position the plate in the desired location. 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.
Because miniplates do not compress the fracture, the fracture must be perfectly reduced prior to application of plates because the plates will not facilitate better reduction as might a compression technique do.
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.
Alternative: 6-hole locking plate 2.0
Illustration showing the final osteosynthesis using a 6-hole locking plate 2.0.
Screws inserted bicortically could provide additional stability when using a medium or large profile 2.0 locking plate.
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 may be released and the occlusion checked.
The arch bar must be maintained for 5-6 weeks to provide a second point of fixation.
4 Case example topenlarge
Simple symphyseal fracture
Example of a simple symphyseal fracture.
Exposure of fracture
Note that a stable arch bar has been applied.
Clinical photographs shows the completed osteosynthesis.
X-ray of the completed osteosynthesis
X-ray shows the completed osteosynthesis