Executive Editor: Marcelo Figari, Gregorio Sánchez Aniceto General Editor: Daniel Buchbinder

Authors: Ricardo Cienfuegos, Carl-Peter Cornelius, Edward Ellis III, George Kushner

Mandible - Symphysis and parasymphysis, simple - ORIF

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Glossary

1 Principles top

Instead of a second screw, a miniplate is applied as a second point of fixation. enlarge

Lag screw fixation

Lag screw fixation uses stabilization by compression that relies on the bony buttressing of the fracture to help stability.

Lag screws should always be placed perpendicular to the bevel of the fracture to prevent displacement of the fragments when the screws are tightened and the bones are compressed.


Lag screw will be placed prior to the miniplate. enlarge

In general, the lag screw is placed prior to the miniplate because the lag screw will compress the fracture, providing better reduction.


Champy’s ideal lines of osteosynthesis for symphyseal fractures. enlarge

Biomechanics of the symphysis

The mandibular symphysis undergoes torsional 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 a lag screws and a plate are applied, they should be separated as much as possible without injuring vital structures.

Illustration shows Champy’s ideal lines of osteosynthesis for symphysis fractures.


Special considerations

Following special considerations may need to be taken into account:

Click on any subject for further detail.

2 Reduction top

How to predrill two monocortical holes below the apices of the teeth enlarge

Drilling monocortical holes

It is necessary to predrill two monocortical holes below the apices of the teeth on either side of the fracture to help place the reduction forceps.

Manipulate the mandible fragments until anatomic reduction is achieved. Apply the reduction forceps and then place the patient into occlusion and secure 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 enlarge

Clamp application

The clamp has to be placed perpendicular to the line of fracture to prevent fracture displacement when tightening the reduction clamp.

3 Lag screw insertion top

Perpendicular positioned screw to the bevel of the fracture enlarge

Sagittal fracture lines

Depending upon the bevel of the fracture, lag screw alignment will vary. For sagittal fractures through the anterior mandible, lag screws placed through the outer cortices from one side to the other within the substance of the mandible (buccal cortex to buccal cortex) provides extremely stable fixation.

Note that the screws and the resultant compression is directed perpendicular to the bevel of the fracture.


Perpendicular positioned screw to the bevel of the fracture enlarge

Oblique fracture lines

For fractures that obliquely pass through the mandible, lag screws are placed from the buccal to the lingual cortices.

Note that the screws and the resultant compression are again directed perpendicular to the bevel of the fracture.


Lag screw insertion enlarge

Lag screw application

Click here for a detailed demonstration of lag screw technique.

4 Plate application top

Contour the plate using bending pliers. enlarge

Plate contouring

Apply a 4-hole miniplate as far away from the lag screw as possible without damaging pertinent anatomy (root apices).

Contour the plate using bending pliers.


Plate can be placed in a direction other than perpendicular to the fracture line. enlarge

Plate positioning

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.


Usage of a 1.5 mm drill bit with 6 mm stop. enlarge

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.


Insertion of a 2.0 mm screw, 6 mm in length. enlarge

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.


Insertion of a second screw on the other side of the fracture. enlarge

Insert second screw

Insert a second screw on the other side of the fracture in the same way.

Tighten both screws.


Completed plate application. enlarge

Additional screw placement

Fill the remaining plate holes with screws.

5 Confirmation of reduction top

Confirm adequate reduction. There should be no gap at the lingual aspect. A gap would lead to occlusal disturbance and mandibular widening.

MMF is released and the occlusion checked.

Because two points of fixation have been applied (one lag screw, one plate), it is not essential that the arch bars remain in position and they can be removed.

6 Case example top

Symphysis fracture of the mandible enlarge

Symphysis fracture of the mandible

X-ray shows fracture through the mandiblar symphysis.


Metal tongue piercing enlarge

Note the metal tongue piercing.


Reduced fracture after exposure enlarge

The fracture is reduced after exposure.


A lag screw is placed in the most favorable area enlarge

After putting the patient into MMF, a lag screw is placed in the most favorable area to accommodate it. In this case, a lag screw was placed at the inferior border of the mandible.


A miniplate is used as a second point of fixation. enlarge

Because of the lack of curvature in the middle of the mandible, a second lag screw was thought not possible. Instead, a miniplate was used as a second point of fixation.


Completed osteosynthesis. enlarge

X-rays show the completed osteosynthesis.


Good occlusion of the mandible enlarge

Outcome

6 weeks postoperatively, the patient had a good occlusion and


Rehabilitation of mandibular opening. enlarge

... rehabilitation of mandibular opening.

v1.0 2008-12-01