return to: Facial Fracture Management Handbook

by Dr. Gerry Funk

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Mandible Fractures

Anatomy and Mechanism of Injury

Many of the fundamental concepts of dental and mandibular anatomy relevant to mandibular fractures has been reviewed in previous sections. In discussing mandible fractures, the mandible is generally divided into several different areas including, symphyseal (or parasymphyseal), body, alveolar process, angle, ramus, coronoid and condyle. The areas most frequently fractured are the condyle, body and angle. Condyle fractures are more likely to occur as a result of forces directed straight posteriorly (uppercut and jab) whereas angle and body fractures are associated with medially directed trauma (the roundhouse punch).

The muscles of mastication tend to distract some types of mandible fractures and reduce others depending on the anatomy of the fracture lines. If the muscle pull distracts the fragments the fracture is unfavorable. If the muscles act to reduce the fracture it is a favorable fracture. Fractures may be vertically or horizontally favorable or unfavorable.

Physical exam

Head and neck exam with special attention to:

1. The initial exam should assess the likelihood of significant floor of mouth swelling or tongue swelling that could potentially compromise the airway.

2. A thorough examination of the oral cavity including dentition, apparent class of occlusion, characterization of the occlusal disharmony present, maximal incisor opening and mucosal surfaces should be undertaken.

3. Palpate the external and intraoral surfaces of the mandible for step off's.

4. Check for cranial nerve V3 function.

5. Inspect the external auditory canals for fractures caused by impaction of the condylar heads.

Emergency Management

The emergency intervention related to mandible fractures centers around airway management. If the airway is tenuous due to floor of mouth or tongue swelling or as the result of associated injuries the appropriate intervention outlined in the introductory section should be undertaken. This in most cases is either nasal intubation over a flexible bronchoscope or tracheostomy. If the patient is unconscious the initial evaluation should include the removal of material from the mouth which could potentially be aspirated (teeth, blood clots, road debris). It is important to realize that airway status is not a constant but a dynamic entity which may change with time as swelling increases. Frequent airway checks early in the course of treatment are prudent. As a general rule if the need for definitive airway management seems likely you should go ahead with it at that time not when it will require an emergency intervention. The emergency management of injured dentition was outlined in the pathophysiology section. Any mandible fracture which transects a dental socket should be considered an open fracture with oral contamination. These patients should be on antibiotics and undergo fracture fixation as soon as possible.

Radiographic Work Up

The single most useful radiologic study to evaluate mandible fractures is the orthopantomogram (Panorex). Towne's views will allow enhanced visualization of the condyles and periapical dental views may be needed to evaluate dental root trauma near fracture lines. In general CT scanning of the mandible for mandible fractures adds little to the above studies.

Definitive Management

Before we look at several of the various methods available for mandibular fracture repair it is useful to discuss some basic principles of bone healing and internal fixation. Bone healing is either indirect by callus formation, which occurs in conditions of relative stability or by direct bone healing which requires the fragments to be opposed in a condition of absolute stability. Indirect bone healing proceeds through several stages, from granulation tissue to fibrous tissue to cartilage to bone. Each stage results in an increase in the strength of the callus and a decrease in the micromotion occurring across the fracture line. There is no micromotion across the fracture line and no callus in direct bone healing. With this type of healing there is no differentiation of connective tissue to cartilage, and healing occurs with the remodeling of Haversian canals in bone fragments brought together in compression (Phillips et al. 1992).

Many of the plate and screw systems used in mandible fractures are designed to bring the mandibular fragments together in a state of compression and promote direct bone healing. The holes in the plates are designed to force the bone fragments together as they are tightened, this is known as compression plating. These special plates are called dynamic compression plates.

During function many bones have a tension and compression side. In general, mandible fractures also have a tension and compression side due to the forces of mastication and shape of the mandible. The inferior cortex is the compression and the alveolar part is the tension side in mandible fractures. We saw earlier that most plates placed on the mandible must be in the inferior cortex area in order to avoid damage to the tooth roots and mental nerve by the screws. Because the tension side tends to distract during function, despite fixation of the compression side, this side must be stabilized with a "tension band." The tension band keeps the tension side of the fracture from distracting. In mandible fractures the tension band can be a small plate placed along the alveolar area (with care to avoid tooth roots) or an arch bar or simply a circumdental wire securing the two teeth on the mesial and distal sides of the fracture together.

The primary goals in the management of mandibular fractures are restoration of functional occlusion and facial form. There are frequently several appropriate techniques available for the definitive management of a given mandible fracture. In general, mandible fractures are treated either closed (maxillomandibular fixation, splinting, modified diet) or open (plates and screws, interosseous wiring, lag screws).The technique chosen depends on a number of variables including, dental status, fracture characteristics (open, closed, favorable, unfavorable, comminution, bone lose, mechanism of injury, contamination or frank infection etc.), fracture location, associated injuries, patient mental status and patient desires. The most important considerations are the dental status, fracture characteristics and fracture location.

Closed techniques involve the relative fixation of mandibular fragments allowing indirect bone healing, which progresses through granulation, fibrosis, cartilage and eventually bone deposition and remodeling. Closed techniques are best used in cases with favorable, closed fractures and in patients with full dentition. Mandible fractures in children heal quite rapidly and because mixed dentition often precludes the placement of screws in the mandible, closed techniques using some form of maxillomandibular fixation are preferred in many pediatric mandible fractures. Condylar neck fractures have traditionally been managed in a closed fashion with a short course of intermaxillary fixation and soft diet. Despite the nonanatomic reduction of the condylar head remodeling occurs over a period of months. Maxillomandibular fixation may be supplemented with interosseous wiring of bone fragments ensuring adequate bone contact and a stable reduction.

Open reduction and internal fixation of mandible fractures is an evolving science. There are a number of different techniques used to internally fixate mandible fractures. Simple interosseous wiring to supplement intermaxillary fixation is a form of open reduction and internal fixation. There are a variety of plate and screw systems available for the repair of mandible fractures. Compression plating of mandibles has become popular over the last 10 years. Compression plate fixation allows direct bone healing and in most cases eliminates the need for 4 to 6 weeks of maxillomandibular fixation needed with closed reduction techniques. Compression plates used on the inferior cortex must always be used with some form of tension band as discussed above. A special type of compression plate called an eccentric dynamic compression plate can be used without a tension band. This plate has sliding ramp holes which allow compression of the fracture not only in the area of the plate but also at the tension side of the mandible. In general the application of compression plates requires that the angle of the fracture be no more than 30 degrees from a line perpendicular to the long axis of the plate. If an angle greater than this exists the compression plate will cause the fragments to slide against one another rendering the reduction nonanatomic and not in compression.

If internal fixation is desired and compression plating cannot be performed due to an oblique fracture or significant comminution of fragments, several other options exist. Reconstruction plates are large plates which use at least three screws on each side of the fracture. They hold the bone in absolute stability and because of their large size and stability, they do not require a tension band. Reconstruction plates are useful in cases of severely comminuted mandible fractures such as those resulting from gunshot injuries. If correctly placed small noncompression plates (called adaptation plates) may be used to repair mandible fractures. The most well known of these systems is the Champy system. One final method of internal fixation of mandible fractures is with lag screws. A lag screw is able to compress two bone fragments and therefore permits direct bone healing. The number of fracture cases suitable for lag screw repair is relatively small and this technique requires considerable experience and skill.

Fractures of the mandible can be approached either transorally or through the neck. In closed fractures one advantage of approaching the fracture through the neck is the absence of salivary contamination of the wound. The obvious drawback in an external approach is a scar. Most symphyseal and body fractures can be easily plated through the mouth. Angle and ramus fractures are difficult to approach through the mouth and if an intraoral approach is performed special instruments for the transcutaneous placement of screws must be available. Patients with open mandible fractures should be on antibiotics active against oral cavity organisms including anaerobes. Perioperative antibiotics have been shown to decrease the rate of wound infections.

References

Phillips,J.H., Rahn,B.A.: Bone Healing. In Rigid fixation of the craniomaxillofacial skeleton. Yaremchuk,M.J., Gruss,J.S., Manson,P.J. (Eds.), pp 3-6, Butterworth-Heinemann, Stoneham, MA, 1992.