1 Principles top
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Biomechanics
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 load-bearing fixation across the basal triangle via an extraoral approach. This can be provided one of two ways:
Using one reconstruction plate or ...
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... 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.
Special considerations
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
- Complications
Click on any subject for further detail.
2 Selection of approach top
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These fractures can often be approached and treated through the intraoral approach.
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However, depending on the difficulty or severity of the fracture, and/or the presence of a laceration suitable, an extraoral approach via the submental route may be indicated.
3 Choice of implant for two plate fixation top
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Superior border plate
The superior border is treated with a tension band plate with monocortical
screw fixation. The profile of this plate can be minimal.
The plate selection can be as follows:
- 4- or 6-hole mandible plate 2.0 with or without center space
- 4- or 6-hole small profile locking plate 2.0 with or without center space
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Inferior border plate
Only large profile plates meet the biomechanical requirements of basal triangular fractures.
One of the following plates should be considered for fixation at the inferior border. The chosen plate should allow for a fixation of the triangle to the plate. This precludes the use of plates with a center space.
- 6- or 8-hole large profile locking plates 2.0
- 6- or 8-hole extra-large locking plates 2.0
Screw application is commonly bicortical.
Further details on screws and plates
4 Reduction top
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MMF
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.
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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.
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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 in an area that will not interfere with the later plate placement.
5 Fixation of superior border plate top
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Plate contouring
The plate is contoured to the outer surface of the superior aspect of the mandible in a position avoiding tooth roots.
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Drill first screw hole
Hold the plate with an appropriate instrument in place (eg, periosteal elevator or forceps).
Use a 1.5 mm drill bit with 6 mm stop to drill monocortically through the plate hole on one side of the fracture.
Note: the cortical bone in this region may be very thin and tooth roots can be damaged even when using a 6mm drill bit with stop.
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Insert screw
Insert a 2.0 mm screw, 6 mm in length. Do not fully tighten it until the final reduction and plate position are confirmed.
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Insert second screw
Insert a second screw in the hole next to the fracture line on the opposite side of the fracture. The periosteal elevator is used now to keep the far end of the plate at the correct vertical level. Tighten both screws. The clamp can be removed afterwards.
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Additional screw placement
Fill the remaining plate holes with screws in an orderly fashion continuing from the plate holes next to the fracture to the outer plate holes.
6 Fixation of lower border plate top
Plate contouring
Contouring of large profile plates is demanding. Usually a straight plate can be inserted at the lower border of the mandibular body overlying the reduced basal triangle. Adjustments to the bony surface must be made by out-of-plane bending.
If one intends to place a screw into the basal triangle, the plate is positioned with at least one hole of the plate overlying the triangle.
The use of a malleable template may be helpful.
The correct plate position and adaptation must be checked either by direct vision or probing with a blunt instrument.
Ensure that the plate is located on bone over its full length so that all screws will engage the bone.
Click here for further details on plate bending.
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Pearl: plate insertion in parasymphyseal fractures
An obstacle to plate placement are the exiting branches of the mental nerve. This area represents a danger zone for nerve damage. The bone region below the branches must be dissected carefully. The plate is positioned in the space below the mental foramen, if necessary. The nerve branches must be mobilized out of the field during the introduction of the plate. During screw placement in the mental nerve area the nerve branches must be protected.
A medium profile locking plate 2.0 is used, in this case at the lower border.
Note that a screw is placed into the basal triangle.
The fixation of the lower border will be illustrated using a 7-hole large profile locking plate with bicortical screw fixation. The basal triangle is prefixed with a miniplate at the apex.
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Drill first screw hole
Hold the plate with an appropriate instrument (eg, periosteal elevator, forceps).
Use a 1.5 mm drill bit to drill bicortically through the plate hole next to the fracture line in one fragment.
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Insert first screw
Prior to screw insertion determine the appropriate screw length using a depth gauge.
Insert a 2.0 mm screw of appropriate length. Do not fully tighten it until the final reduction and plate position are confirmed.
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Insert second screw
Insert a second screw in the hole next to the fracture line in the opposite fragment. The periosteal elevator is used now to keep the far end of the plate at the correct vertical level.
Tighten both screws.
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Additional screw placement
Fill the remaining plate holes with screws in an orderly fashion continuing from the plate holes next to the fracture to the outer plate holes.
Finally the basal triangle is secured with additional screws as necessary. A locking head screw is preferred over a conventional screw to avoid secondary displacement of the basal triangle. The screw can be inserted either monocortically or bicortically depending whether the triangle is separated or not.
Removal of miniplate
If an additional miniplate was used for fracture simplification, it can be removed.
Final check
Release the MMF and check the occlusion for accuracy and the bony surfaces for precise anatomic reduction.
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Final osteosynthesis
Clinical photograph showing the final osteosynthesis.