1 Principles topenlarge
The basal triangle decreases the bone buttressing and the interfragmentary
support. This condition demands a degree of stability beyond the level of low
degree load sharing.
Symphyseal basal triangular fractures therefore should be considered comminuted fractures requiring a level of high degree load-sharing or load-bearing fixation across the basal triangle. This can be provided one of two ways:
Using one reconstruction plate or ...
... using two plates, but the one along the inferior border being a heavy locking plate 2.0 of large or extra-large profile.
Sequence of plate insertion
The superior plate is inserted first. This will prevent inadvertent displacement of the fragments during the subsequent contouring and insertion of the inferior border plate.
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 Reduction topenlarge
In symphyseal fractures with basal triangular fragments, an arch bar is preferred for MMF.
The application of the arch bar is unproblematic because only one fracture line runs through the alveolar process and is not affected by the triangular fragmentation.
Click here for a description of MMF application.
Reduction of the main fragments
Reduction of the fragments is done manually with the use of elevators, bone hooks, or bone screws inserted as handles. Gross reduction is done prior to the MMF application. Fine tuning for precise anatomical reduction is best done with MMF in place.
The main fragments are reduced as a first step. Ensure that the basal triangle is loose enough be reduced secondarily into the remaining bone gap.
From evaluating the preoperative x-rays it is assumed that the basal triangle is a single and solid bony triangle. It becomes apparent from CT scanning that basal triangles are often divided into an outer and inner table fragment which makes the reduction more difficult. The inner fragment will not usually be accessible using an intraoral approach that only exposes the anterior surface of the mandible.
Reduction of the basal triangle
The basal triangle itself must be repositioned by pushing and dragging with an appropriate instrument. Bone screws inserted into the basal triangle function well as a handle on the fragment and are useful for reduction. Using a transoral approach the lingual cortex of the mandible can be accessed only with addition of a percutaneous hook.
To keep the basal triangle in position it can be compressed between the greater fragments. An alternative is the preliminary fixation with a miniplate that does not interfere with the planned position of the inferior border plate.
Maintaining the reduction
The maintenance of the reduction of the alveolar portion of the fracture with a conventional clamp becomes more difficult the higher the basal triangle is located. If the basal triangle segment is large and extends superiorly, the reduction clamp can actually “squeeze out” the fragment. If possible, a clamp is applied into tiny predrilled holes in the outer cortex.
3 Fixation topenlarge
For load-bearing fixation, a locking reconstruction plate 2.4 should be used. The plate must be long enough so that there can be a minimum of three or preferably four screws on each side of the fracture. The screws adjacent to the fracture should be at least 7 mm away from the fracture line. Most commonly there will be one or two holes without screws located over the fracture. There are advantages to using a locking reconstruction plate system. Click here to learn about them.
The plate must be contoured to the surface of the mandible flush with the inferior border to avoid injuring the mental and inferior alveolar nerves.
Click here to see a step-by-step description of plate bending using locking reconstruction plate.
Threaded drill guides should always be used to center the screw within the locking reconstruction plate.
For a step-by-step description of screw insertion into locking reconstruction plates follow this link.
Large fragments (like the triangular one in this illustration) can be secured to the plate to hold them in position.
One should then release the MMF and check the occlusion for accuracy before proceeding with closure.
4 Case example topenlarge
Panoramic and ...
... PA x-rays show a large basal triangular fracture of mandibular symphysis.
Fracture-related preoperative malocclusion.
Large basal triangle
Intraoperative photograph shows large basal triangle that has not yet been reduced. Note that the alveolar components have been reduced.
Intraoperative photograph shows bone clamps used to reduce basal triangle.
Intraoperative photographs show completed osteosynthesis.
Note that small miniplates were used to maintain position of basal triangle after it was reduced with clamps.
Postoperative x-rays show ...
... reduction and fixation.