One example of load-sharing osteosynthesis is the use of compression plates. The forces of mastication are overcome by the plate and the bony buttressing at the fracture site. This technique ensures good interfragmentary compression and thus good bony buttressing at the fracture site.
The trend in fracture management is moving away from use of compression plating which is very sensitive and carries a higher complication rate if not performed perfectly.
Compression plating technique is generally considered to be a two plate technique. However, a dental arch bar and acrylic can suffice as the superior tension band plate.
|Indications and contraindications|
Indications for compression plating would include any fracture that has excellent bony buttressing, for example most simple fractures.
Compression plating is contraindicated when there is not good bony buttressing at the fracture site, as is seen in atrophic edentulous mandible fractures, defect fractures, comminuted fractures, and other complex mandibular fractures.
It is also contraindicated in simple fractures with an extreme oblique pattern (sagittal fractures) that are often suitable for compression osteosynthesis using lag screw fixation.
Compression is obtained by tightening screws down a ramped hole design. This is the spherical gliding principle. The compression holes are drilled eccentrically to allow for compression. Typically, the holes on either side of the fractures are designated for compression screw placement. Additional plate holes are drilled centrically and compression is not used.
A) Plate with ramped holes facing outward to be used in compression plating
B) Undersurface of plate showing limited contact (LC) to minimize pressure on the cortical bone underneath the plate.
C) Template to assist in plate contouring
As the eccentrically placed compression screws are tightened, the head moves down the ramp and the bone is compressed together.
Illustration showing two eccentrically inserted but not fully tightened screws.
The left screw is fully tightened and thereby narrowing the gap.
Tightening the right screw finally compresses the fracture. Please note that the compression screws are bicortical in nature.
The plate must be overbent slightly to close the lingual cortex. It must be overbent in all areas of the mandible where compression plating is used.
- Plate overbent approximately 1mm and not touching buccal cortex.
- Gap in lingual cortex present.
As compression screws are tightened, the slightly overbent plate closes the lingual gap.
Pitfall: gap at lingual cortex
If the plate is not slightly overbent, the buccal cortex will be well aligned but a gap remains at the lingual cortex.
|Eccentric drilling for compression|
There are two drill guides used with compression plating. The yellow drill guide is used for eccentric hole placement. The green drill guide is used for neutral hole placement.
To drill eccentrically, the arrow on the yellow end of the drill guide must point towards the fracture. The number close to the arrow shows the maximal possible amount of bone movement upon screw insertion.
|Drilling in neutral position|
To drill in the neutral position, the green end of the drill guide must be used.
|Option for off-angle drilling|
There are times when off-angle drilling is necessary to avoid anatomic structures such as tooth roots.
Although the hole does not have to be drilled at 90° to the bone it should not enter the fracture, and it should not be angled in such a way that it interferes with the adjacent screws.
Illustration showing the eccentric position of the drill hole in relation to the plate hole.
|Additional tension band|
An arch bar can not be used here as tension band and therefore a plate will be used instead.
A miniplate with screws inserted monocortically is used to avoid damage to the tooth roots.
Heavier compression plates (at least 4-hole) is placed at the inferior border (compression zone).
Both plates together function to reconstruct both the tension and pressure trajectories of the mandible.
The inferior alveolar nerve region is considered as the neutral zone of the mandible. Avoid plate and screw fixation in this area that would damage the nerve.
|Compression plating technique|
Aminiplate is placed with one screw on either side of the fracture to align and stabilize the fragments.
The compression plate is adapted and eccentric hole is drilled on either side of the fracture.
To place an eccentric hole, the proper gold drill guide must be used and the arrow must point toward the fracture.
Once both the eccentrically placed screws are tightened, the fracture is compressed. There is no need to compress the fracture additionally so the remaining screws are placed in a neutral position. The appropriate green drill guide is used to place the neutral screws.
Compression plating is completed. Screws used for the compression plate are bicortical in nature.
Reminder: the tension band miniplate uses screws inserted monocortically.
The remaining screws are placed in a monocortical fashion in the upper plate.
Illustration shows the completed osteosynthesis.