Authors of section

Authors

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

Executive Editors

Marcelo Figari, Gregorio Sánchez Aniceto

General Editor

Daniel Buchbinder

Open all credits

ORIF, lag screws

1. Principles

Lag screw fixation

Lag screw fixation uses stabilization by compression that relies on the bony buttressing of the fracture to help stability.
One reason why the mandibular body is well suited to lag screw fixation is the thickness of the bony cortices which provide extremely secure fixation when the screws are properly inserted, providing interfragmentary compression.

Click here for a detailed description of the lag screw technique and its biomechanical principles.

Lag screw fixation in body fractures

Zones for screw placement in the mandibular body

There are two intrabone structures that must not be harmed by screw insertion: the mandibular canal and the tooth roots.

Danger zone – “no mans land”
The classical description for screw placement in plate and screw osteosynthesis is depicted for orientation. Monocortical screws can be inserted above the level of the mandibular canal. The use of bicortical screws is restricted to the area below the course of the nerve canal at the level of the lower mandibular border.

Lag screw fixation in body fractures

Variations of mandibular canal and alveolar nerve

There may be variations of the course of the mandibular canal and the alveolar nerve. The standard situation is depicted in the previous step, but the vertical height of the canal can be located next to lower border of the mandible (as illustrated here).

The alveolar nerve itself can consist of a single bundle inside the canal but it can also spread in a plexus formation inside the overall bony cross-section of the mandible. These situations prevent the usual screw insertion and require an individual screw and/or plate placement.
Click here for further information on principles of the inferior alveolar nerve.

Lag screw fixation in body fractures

Screw insertion pattern

Screw insertion can be done in a serial pattern at the lower border of the mandible.

Lag screw fixation in body fractures

Alternatively, screws can be placed in a tripod fashion using the lower and the upper insertion zone. In the upper zone, the anatomic relation between the nerve canal and the tooth apices varies. Sometimes there is no space between the tooth apices and the nerve, which is a clear contraindication to follow this pattern.

Using the lag screws in a tripod fashion provides additional stability. Note how the superior screw avoids both the dental roots and the alveolar nerve in the illustration.

Lag screw fixation in body fractures

Number of screws

In order to withstand rotational forces a minimum of two screws is required. For additional stability it is recommended to use at least three screws especially if 2.0 mm screws are applied.

Special considerations

2. Selection of approach

These fractures can often be approached and treated through the intraoral approach.

orif two plates basal triangle

However, depending on the difficulty or severity of the fracture, and/or the presence of a laceration suitable, an extraoral approach via the submandibular route may be indicated.

orif reconstruction plate basal triangle

3. Reduction

Clamp application

In a first step the patient is placed into MMF. The bony fragments are then reduced manually.

A fixation clamp can be applied to maintain the reduction. Therefore, a towel clamp may be used transcutaneously to keep the reduction at the lower border with the prongs coming in from the medial side and laterally. Usually, there should be no risk of injuring the marginal mandibular branch of the facial nerve. The accessibility to the lower border may be compromised by the towel clamp.

Lag screw fixation in body fractures

With a large dimension reduction forceps it is possible to prefix the lateral fragment in a sagittal fracture configuration to the contralateral outer cortex. On the contralateral cortex the prong is applied transmucosally.

Lag screw fixation in body fractures

Alternative: MMF

Another method to maintain the reduction is the use of MMF screws. They must be applied monocortically in the posterior fragment. All screws in the lower jaw must be integrated into an appropriate cerclage with the maxillary counterpart to keep the fragments aligned. The posterior fragment should have traction to the anterior maxilla and vice versa.

In this case an arch bar is not suited for reduction of the fragments. It can fix only one of the fragments via the teeth. This will usually be the larger anterior fragment.

Lag screw fixation in body fractures

4. Fixation

General consideration

The vertical angulation of the screw should be varied as far as possible to meet the bevel of the fracture at 90° and to provide an uninterrupted approximation of the inner and outer fragment during the compression process.

Lag screw fixation in body fractures

Alternative: transbuccal system

The use of the transbuccal system may become necessary in the dorsal caudal region of the mandibular body, which is inaccessible transorally with a screw driver.
Click here for a detailed description of the transbuccal system.

Lag screw fixation in body fractures

Maximal stability between the fragments is achieved by compressing the rough surfaces of the fracture interface as it yields maximum frictional effect.

A crucial point is the choice of the appropriate screw length so that the far tip of the screw fully engages the far cortex with the screw tip exiting slightly above the bony surface.

Click here for a detailed demonstration of lag screw technique.

Lag screw fixation in body fractures

Completed osteosynthesis

The MMF is now released. A control of the final reduction is hardly possible by clinical assessment. Only the anterior outer fracture line can be checked for accurate alignment. The internal bony situation will only be deduced from the general control of the occlusion and articulation. The anatomic reduction can only be assessed postoperatively with 3-D imaging techniques.

Illustration shows the completed osteosynthesis with fully inserted bicortical screws.

Lag screw fixation in body fractures

X-ray shows completed osteosynthesis

Lag screw fixation in body fractures

5. Case example

Diagnosis

In this case the sagittal fracture line runs in transitional zone between the posterior body and the angle.

Lag screw fixation of body fractures

Lag screw insertion

According to the principle, lag screws are inserted perpendicular to the fracture line. Three screws of different length were inserted to fully engage the far cortex.

Lag screw fixation of body fractures

Completed osteosynthesis

The X-ray shows the completed osteosynthesis.

Lag screw fixation of body fractures

6. 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.