Authors of section


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

Executive Editors

Marcelo Figari, Gregorio Sánchez Aniceto

General Editor

Daniel Buchbinder

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ORIF, two lag screw fixation

1. Principles

Lag screw fixation

Lag screw fixation uses stabilization by compression that relies on the bony buttressing of the fracture to help stability (load-sharing osteosynthesis).

Lag screws should always be placed perpendicular to the fracture plane to prevent displacement of the fragments when the screws are tightened and the bones are compressed.
Click here for a detailed description of the lag screw technique and its biomechanical principles

Lag screw fixation

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 two lag screws 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.

Champy's ideal lines of osteosynthesis for symphysis fractures

Special considerations

Teaching video

AO Teaching video on lag screw insertion

2. Approach

For this procedure the intraoral approach to the symphysis is normally used.

orif one plate and arch bar

3. Reduction

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.

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

Clamp application

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

The clamp has to be placed perpendicular to the line of fracture

4. Fixation

Lag screw insertion

Depending on the fracture plane orientation, 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) provide extremely stable fixation.

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

Perpendicular positioned screw to the bevel of the fracture

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.

Perpendicular positioned screw to the bevel of the fracture

Click here for a detailed demonstration of lag screw technique.

Lag screw technique

Number of screws

In general, a minimum of two lag screws should be used to provide stable internal fixation of mandibular symphysis fractures.
Because the symphysis undergoes twisting during function, a single lag screw cannot prevent such motion from occurring.

Stable internal fixation of mandibular symphysis fracture

Alternative: screws placed from opposite sides

Occasionally it is more convenient to place screws from opposite sides. From a biomechanical standpoint it is irrelevant.

Screws placed from opposite sides

Confirmation of reduction

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

MMF should be released and the occlusion checked.

Because two points of fixation have been applied (two lag screws), it is not essential that the mandibular arch bar remains in position to function as another point of fixation

Confirmation of reduction

Completed osteosynthesis

X-ray shows the completed osteosynthesis.

Completed osteosynthesis

5. Aftercare following ORIF of mandibular symphysis, body, angle and ramus fractures

If arch bars or MMF screws are used intraoperatively, they are usually removed at the conclusion of surgery if proper fracture reduction and fixation have been achieved. Arch bars may be maintained postoperatively if functional therapy is required or if required as part of the fixation.

Postoperative x-rays are taken within the first days after surgery. In an uneventful course, follow-up x-rays are taken after 4–6 weeks.

The patient is examined approximately 1 week postoperatively and periodically thereafter to assess the stability of the occlusion and to check for infection of the surgical wound. During each visit, the surgeon must evaluate the patients ability to perform adequate oral hygiene and wound care, and provide additional instructions if necessary.

Adequate dental care is required in most patients having suffered a mandibular fracture.

If a malocclusion is detected, the surgeon must ascertain its etiology (with appropriate imaging technique). If the malocclusion is secondary to surgical edema or muscle splinting, training elastics may be beneficial. The lightest elastics as possible are used for guidance, because active motion of the mandible is desirable. Patients should be shown how to place and remove the elastics using a hand mirror.

If the malocclusion is secondary to a bony problem due to inadequate reduction or hardware failure or displacement, elastic training will be of no benefit. The patient must return to the operating room for revision surgery.

Follow-up appointments are at the discretion of the surgeon, and depend on the stability of the occlusion on the first visit. If a malocclusion is noted and treatable with training elastics, weekly appointments are recommended.

Postoperatively, patients will have to follow three basic instructions:

1. Diet
Depending upon the stability of the internal fixation, the diet can vary between liquid and semi-liquid to “as tolerated”, at the discretion of the surgeon. Any elastics are removed during eating.

2. Oral hygiene
Patients having only extraoral approaches are not compromised in their routine oral hygiene measures and should continue with their daily schedule.
Patients with intraoral wounds must be instructed in appropriate oral hygiene procedures. The presence of the arch-bars and any elastics makes this a more difficult procedure than normal. A soft toothbrush (dipping in warm water makes it softer) should be used to clean the surfaces of the teeth and arch-bars. Any elastics are removed for oral hygiene procedures. Chlorhexidine oral rinses should be prescribed and used at least three times each day to help sanitize the mouth. For larger debris, a 1:1 mixture of hydrogen peroxide/chlorhexidine can be used. The bubbling action of the hydrogen peroxide helps remove debris. A Waterpik® is a very useful tool to help remove debris from the wires. If a Waterpik is used, care should be taken not to direct the jet stream directly over intraoral incisions as this may lead to wound dehiscence.

3. Physiotherapy
Physiotherapy can be prescribed at the first visit and opening and excursive exercises begun as soon as possible. Goals should be set, and, typically, 40 mm of maximum interincisal jaw opening should be attained by 4 weeks postoperatively. If the patient cannot fully open his mouth, additional passive physical therapy may be required such as Therabite or tongue-blade training.