Mandibular Symphyseal and Parasymphyseal Fractures 

Updated: Feb 18, 2020
Author: William D Clark, MD, DDS; Chief Editor: Arlen D Meyers, MD, MBA 

Overview

History of the Procedure

Mandible fractures are described in early Egyptian writings. Hippocrates advocated the use of bandages and interdental wiring for the treatment of mandibular fractures. In a 3-part article published during the Civil War, Gunning wrote of using dental splints attached to elaborate external appliances. In 1881, Gilmer first described the use of bars on both arches, fixed to the teeth and to each other with fine wire ligatures.[1]

The first mandibular bone plating is credited to Schede, who is said to have used a steel plate screwed to the mandible in the late 1880s. In 1934, Vorschutz described external fixation using transdermal bone screws and plaster. The Morris biphase is a refinement of that technique.

History of rigid internal fixation devices is ongoing, with a new theory and a corresponding set of devices appearing every few years.[2, 3, 4, 5, 6]

Problem

Fractures that occur in the midline of the mandible are classified as symphyseal. When teeth are present, the fracture line passes between the mandibular central incisors. Fractures occurring in the area of the mandible from cuspid to cuspid, but not in the midline, are classified as parasymphyseal (as seen in the image below). The treatment of these types of fractures differs little, if at all; therefore, they are discussed together.

The broad red line indicates the symphyseal area. The broad red line indicates the symphyseal area. The pink area between the cuspid teeth, excepting the symphysis, indicates the parasymphyseal area.

Epidemiology

Frequency

In the United States, the incidence of facial fractures of the mandible is second only to that of the nose. Fractures of the symphysis/parasymphysis region account for approximately 10% of mandibular fractures, which makes this the fourth most common region to be fractured.[7]

A study by Morris et al found the proportion of various types of mandibular fractures (4143 fractures; 2828 patients) to be as follows[8] :

  • Angle (27%)
  • Symphysis (21.3%)
  • Condyle and subcondyle (18.4%)
  • Body (16.8%)

A study by Jung et al of 1172 mandibular fractures (735 patients) found the symphysis to be the most frequent fracture site, accounting for 431 fractures (36.8%).[9]

The major difference in mandible fractures in countries other than the United States concerns etiology of fractures.[10] In some locations, vehicular trauma is a lesser cause because of a relative lack of vehicular transportation. Interpersonal facial trauma tends to be of lower energy than vehicular trauma, thus resulting in generally less severe injuries. Most countries other than the United States have fewer incidents with civilian firearms and a correspondingly lower incidence of penetrating trauma.

Etiology

The etiology of symphyseal and parasymphyseal fractures is largely from trauma from interpersonal violence or motor vehicle accidents. Falls, industrial accidents, and sports injuries are lesser etiologies. Most trauma is blunt, but penetrating trauma is common with interpersonal violence and war injury.

Pathophysiology

Blunt trauma can injure any part of the mandible. A sharp blow applied anteriorly often fractures the symphyseal/parasymphyseal region and the condyle region or regions. Blunt force applied broadly across the body of the mandible may also result in a fracture of the symphyseal/parasymphyseal region.

Presentation

The patient has a history of trauma. Pain and tenderness are present about the anterior mandible, and the patient reports malocclusion. False motion of the mandible is usually evident.

Preoperative examinations are often impaired by tenderness and masticatory muscle spasm; therefore, a thorough reexamination of the face and oral cavity is performed prior to definitive therapy. The entire mandible is carefully inspected and palpated. All teeth are inspected and evaluated for injury and mobility. A survey of the dental arches is completed to detect any sockets missing teeth. The maxilla is examined to detect any previously missed injuries.

Indications

Presence of a symphyseal/parasymphyseal fracture is the indication for treatment. Mode of treatment varies among patients.

Relevant Anatomy

Fractures of the symphysis/parasymphysis are inherently unstable. Muscles of mastication insert into posterior portions of the mandible with a net effect of superior rotation about the axis of the temporomandibular joint. The suprahyoid muscles of the neck act directly on the anterior mandible, with a net effect of inferior rotation around the axis of the temporomandibular joint and scissoring motion around a vertical axis through the symphysis. The later action is from the mylohyoid muscles.

Fractures of the anterior mandible lack 2 of the stabilizing factors provided to fractures of the posterior tooth-bearing mandible: the splinting effects of the masseter and internal pterygoid muscles, which form a natural sling, and the interlocking cusps and fossae of bicuspid and molar teeth.

Contraindications

The only absolute contraindication to managing these fractures exists if the patient is not stable enough to undergo the needed treatment. A specific contraindication for maxillomandibular fixation (MMF) is poorly controlled seizures. Patients with uncleared cervical spines present limitations regarding which treatment for facial fractures is safe.

 

Workup

Laboratory Studies

No lab studies are needed to evaluate these fractures; however, they may be indicated in the evaluation of associated injuries.

Imaging Studies

See the list below:

  • Computed tomography (CT) scans have become the criterion standard for evaluating the mandible for fractures.

  • In patients with multiple traumas, many emergency departments obtain near whole-body CT scans, which may provide useful information.

  • The panoramic dental radiograph is an excellent tool for imaging the traumatized mandible. When the needed equipment is not available or the patient cannot be placed in the apparatus, plain radiographs of the mandible may be sufficient.

  • Three-dimensional reconstructions of CT scans can be useful to evaluate complex mandibular fractures. The ultimate imaging tool is the stereolithographic model, which some centers are able to make from CT scan images. These are life-size models of the facial bones made of a plastic resin that can be handheld. They can be useful in planning treatment and may be used as templates for contouring rigid hardware or constructing splints and other adjunctive appliances.

  • Evaluation of the entire mandible is important because multiple fractures are common. If the blow was directed at the anterior arch of the mandible, excluding fractures of the subcondylar areas is mandatory.

 

Treatment

Medical Therapy

Essentially all symphyseal and parasymphyseal fractures are open to the mouth and, thus, are grossly contaminated. Antibiotic coverage is essential through the time of initial treatment and early healing. Penicillin is the drug of choice.

Analgesics of mild-to-moderate strength may be prescribed as required, taking care to consider any associated injuries that may contraindicate their use or limit their dose. Acetaminophen in liquid or tablet form may be sufficient. Requests for stronger analgesia should prompt the treating surgeon to consider that the patient may have unrecognized injuries, complications, or substance abuse.

Surgical Therapy

Occasionally, fractures on the anterior mandible are nondisplaced and stable. In this instance, MMF for 6 weeks suffices as treatment. Most fractures are displaced and unstable, requiring a more aggressive approach to therapy.

Before rigid internal fixation became popular, symphyseal and parasymphyseal fractures were usually treated with open reduction with interosseus wiring combined with MMF. In some patients, a lingual splint was required to affect the desired degree of stability. In recent years, open reduction with plate or lag screw synthesis has become popular.

Preoperative Details

A medically stable patient with a mandible fracture should receive definitive care as soon as is practical. Numerous studies have demonstrated that delays in treatment increase the complication rate and reduce the chance of obtaining the best surgical result. The prerequisites for definitive care of these patients are imaging studies sufficient to evaluate their injuries (see Imaging Studies), a stable patient, evaluation by the anesthetist, and informed consent. The anesthesia team needs to know that nasal intubation is required.

Intraoperative Details

The patient is placed in the supine position and nasally intubated by the anesthesia team. Usually, headlights offer the best illumination. Surgical treatment of mandibular fractures often includes the use of sharp objects (eg, wire, screws, arch bars). Therefore, attention to detail is required to minimize the risk of glove puncture.

True sterile preparation of the operative site for repair of mandible fractures is not possible. The extent of preparation to create a clean and disinfected field is controversial. Some clean the teeth, gingivae, and alveolar mucosae with a toothbrush and 3% hydrogen peroxide. The face is painted with povidone iodine solution. If a skin incision is necessary for an open reduction of another fracture, a typical povidone iodine soap scrub preparation is performed.

Prior to exposing the fracture line, the patient is placed in MMF. This accomplishes a gross reduction of the fracture, places the posterior teeth into occlusion, and produces some stability at the alveolar margin. The fracture site may be approached via an intraoral incision, extraoral incision, or laceration. After adequate exposure of the fracture lines, anatomic reduction is achieved. Inspection of the occlusion and alignment of teeth on either side of fracture lines should confirm that proper reduction has been accomplished.

Rigid hardware is then placed with attention to the technique appropriate for the system chosen. When using the Champy miniplate system, 2 plates are required: 1 at the inferior margin and the other at the alveolar level as seen in the image below.

Two miniplates are required for the symphysis/para Two miniplates are required for the symphysis/parasymphysis region because it is subjected to torsional forces, which would be poorly resisted by one miniplate.

When using the titanium craniofacial system techniques established by the Arbeitsgemeinschaft für Osteosynthesefragen/Association for the Study of Internal Fixation (AO/ASIF), tension banding at the alveolar level is required as seen in the image below. This may be in the form of an alveolar miniplate, dental appliance, or the mandibular arch bar. To avoid distraction at the lingual surface of the mandible, dynamic compression plates should be overcontoured by 3-5°.

Tension banding is required to prevent splaying of Tension banding is required to prevent splaying of the fracture line at the superior surface of the mandible when using a dynamic compression plate. A mandibular arch bar can accomplish this. In this example, a miniplate is used.

When the fracture is midline, an alternative to plate fixation is the use of opposing lag screws as seen in the image below. The fracture must be anatomically reduced prior to drilling the holes. In choosing the locations for the screws, care is taken to avoid tooth roots. Drill holes are made to accommodate the chosen screw size, and the hole on the side to receive the screw head is enlarged to the next larger size. Beveling of this side may also be desirable to receive the screw head. The enlargement of the screw-head side prevents the screw from purchasing bone in that fragment. This results in one hemimandible being pulled tightly against the other. This is not a method for the inexperienced surgeon, and it requires careful planning and exacting technique.

Opposing lag screws have been used to treat a symp Opposing lag screws have been used to treat a symphyseal fracture. This procedure requires precise technique and is not for the occasional operator.

Interosseus wiring is an alternative to rigid fixation and is used when rigid devices and their support systems are not available or when the surgeon prefers this technique. A 2-hole figure-8 wire is the standard, with drill holes placed about 1 cm from the fracture line and 1 cm from the inferior border of the mandible. When using nonrigid techniques such as this, consider using a lingual splint for additional stability.

After placement of rigid internal fixation, most surgeons remove the patient from MMF. An exception exists when additional fractures requiring MMF are present. The most common site for such a fracture is the condylar area. These fractures are often treated by MMF only and are often associated with symphyseal/parasymphyseal fractures.

If interosseus wiring is used, MMF is required for 4-6 weeks.

Postoperative Details

Analgesics and antibiotics are indicated postoperatively. Analgesics are usually required for several days. Antibiotics for 7-10 days postoperatively should provide good infection prevention.

If MMF is used, precautions to help prevent and/or deal with nausea and vomiting are paramount. The nursing staff needs specific instructions on measures to take with nausea and/or impending vomiting. Prophylactic use of antiemetics is a strategy used by some. Others order antiemetics be given at the first hint of nausea. If the MMF technique includes having wires hold the teeth in occlusion, a wire-cutting device should be with the patient for the first day. Many place the wire cutters on a tracheostomy tape around the patient's neck.

Follow-up

After discharge from the hospital, the patient should be seen weekly and as needed. Nutritional status, wound healing, oral hygiene, maintenance of secure occlusion, and signs of infection should be assessed during weekly examinations.

For excellent patient education resources, visit eMedicineHealth's Oral Health Center. Also, see eMedicineHealth's patient education articles Broken Jaw and Broken or Knocked-out Teeth.

Complications

Malunion/malocclusion is the most common major complication and results from inadequate reduction and/or loss of reduction during the healing process.

Infection is usually localized and usually responds to antibiotics. Collections of pus should be drained, and hardware, if any, may require removal.

Exposure of implanted hardware requires removal of hardware.

Nonunion is an uncommon complication. It requires that the fracture lines be exposed and freshened with reapplication of fixation and may require bone graft in extreme cases.

Outcome and Prognosis

A united fracture with normal dental occlusion is the expected outcome. Once this result is obtained, the prognosis for the future is excellent.

Future and Controversies

The choice of specific internal fixation systems for mandibular fractures is controversial. Some systems use dynamic compression with bicortical plates while others use noncompressing monocortical plates. Some experienced clinicians feel that interosseus wiring with MMF yields equal results without the disadvantages of open reduction with plate osteosynthesis.

The best route to the mandible for internal fixation is also debated, with some favoring an intraoral approach while others advocate an extraoral incision. Most favor the intraoral approach because an increased infection rate does not seem to be associated with this route.

The future will undoubtedly bring the evolution of newer and better plating systems. Use of stereolithography to aid in planning complex cases may become routine.

 

Medication

Medication Summary

The goals of pharmacotherapy are to prevent infections and complications and to reduce morbidity.

Antibiotics

Class Summary

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

Penicillin G aqueous (Pfizerpen-G)

Penicillin G interferes with the synthesis of cell wall mucopeptide during active multiplication, resulting in bactericidal activity against susceptible microorganisms.

Amoxicillin (Moxatag)

Amoxicillin interferes with synthesis of cell wall mucopeptides during active multiplication, resulting in bactericidal activity against susceptible bacteria.

Analgesics, Other

Class Summary

Pain control is essential to quality patient care. Analgesics ensure patient comfort, promote pulmonary toilet, and have sedating properties beneficial to patients who experience pain.

Acetaminophen (Acephen, Feverall Childrens, Little Fevers, Tylenol 8 Hour, O-Pap, Valorin)

May block pain impulse generation by inhibiting the synthesis of prostaglandin in the central nervous system.