1 Principles topenlarge
The basal triangle decreases the bone buttressing and the interfragmentary support. This condition demands a degree of stability beyond pure load sharing.
Basal triangle fractures through the mandibular angle therefore should be considered as comminuted fractures requiring load-bearing fixation across the basal triangle. This can be provided one of two ways:
Using a reconstruction plate or ...
... using two plates, but the one along the inferior border must be a heavy mandible plate.
Sequence of plate insertion
The superior plate is inserted first in order to achieve preliminary fixation. This will prevent inadvertent displacement of the fragments during subsequent contouring and the insertion of the inferior border plate.
Choice of implant
Locking versus nonlocking plates
There are several advantages to a locking plate/screw system:
- Conventional plate/screw systems require precise adaptation of the plate to the underlying bone. Without this intimate contact, tightening of the screws will draw the bone segments toward the plate, resulting in alterations in the position of the osseous segments and the occlusal relationship. Locking plate/screw systems offer certain advantages over other plates in this regard; the most significant being that it becomes unnecessary for the plate to intimately contact the underlying bone in all areas. As the screws are tightened, they "lock" to the plate, thus stabilizing the segments without the need to compress the bone to the plate. This makes it impossible for the screw insertion to alter the reduction.
- Another potential advantage in locking plate/screw systems is that they do not disrupt the underlying cortical bone perfusion as much as conventional plates, which compress the undersurface of the plate to the cortical bone.
- A third advantage to the use of locking plate/screw systems is that the
screws are unlikely to loosen from the plate. This means that even if a screw
is inserted into a fracture gap, loosening of the screw will not occur.
Similarly, if a bone graft is screwed to the plate, a locking head screw will
not loosen during the phase of graft incorporation and healing. The possible
advantage to this property of a locking plate/screw system is a decreased
incidence of inflammatory complications due to loosening of the hardware.
Locking plate/screw systems have been shown to provide more stable fixation than conventional nonlocking plate/screw systems.
Click here for a description of locking plate principles versus conventional plating.
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
Reduction of major fragments – applying MMF
Open reduction and stable internal fixation in dentate patients begins with fixation of the occlusion. Prior to placing the patient into MMF, the fracture should be exposed and any extractions deemed necessary performed. The superior border of the fracture through the angle should also be reduced prior to placing them into MMF.
Click here for further details on methods for applying MMF.
It is not necessary to have the basal triangle reduced at this stage.
Maintenance of reduction by application of a miniplate 2.0 at the superior border
A miniplate 2.0 is applied along the superior border of the fracture to maintain the alignment and reduction of the major fragments while the inferior border plate is adapted and applied.
The miniplate can be placed either on the lateral surface of the mandible or along the inside of the external oblique ridge similar to the treatment of a simple mandibular angle fracture.
Drill first screw hole
Hold the plate with an appropriate instrument (eg, periosteal elevator or forceps).
Use a 1.5 mm drill bit to drill through the plate hole next to the fracture line in the anterior fragment.
Insert first screw
Insert a 2.0 mm screw of appropriate length. Do not fully tighten it until the final reduction and plate position are confirmed.
Insert second screw
Insert a second screw in the hole next to the fracture line in the posterior
fragment. The periosteal elevator is used now to keep the far end of the plate
at the correct vertical level.
Tighten both screws.
Additional screw placement
Fill the remaining plate holes with screws.
Reduction of the basal triangle
The basal triangle itself must be repositioned by pushing and dragging it 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, a small bone hook can be used to help position this fragment.
To keep the basal triangle in place it can be compressed between the greater fragments. An alternative is the preliminary fixation with a miniplate that will not interfere with the planned position of the inferior border plate.
3 Fixation topenlarge
A 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 stable fragment. Preangled reconstruction plates may be necessary to provide an adequate number of screw holes. There are advantages to using a locking reconstruction plate system (Click here for more details).
Contouring of large profile plates is demanding. Usually a straight plate can be inserted at the lower border of the mandibular angle 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 by 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.
Securing the plate to the bone with bone clamps
Insert the properly contoured plate onto the lateral surface of the mandible and hold it there using ball pointed reduction forceps. Ideally, one set of forceps would be applied anterior and one set posterior to the area of comminution.
The sequence of screw insertion is not important if the plate is securely
clamped to the bone. Threaded drill sleeves should always be used to center the
screw within the plate hole.
For step-by-step description follow this link.
Large fragments (like the triangular one in this illustration) can be
secured to the plate to hold them in position. A locking head screw is a better
choice for this purpose.
If the basal triangle is fixed to the large plate at the lower border of the mandible, any miniplates used for prefixation can be removed. Otherwise, the miniplate(s) can be left in place.
Option: removal of superior border plate
One may choose to remove the miniplate at the superior border or it may be
left in position.
Illustration of the final result after removal of the superior border miniplate.
Release the MMF and check the occlusion for accuracy and the bony surfaces for precise anatomic reduction.
The incision is then closed in layers.