Introduction
Background
Given its prominent anatomic location, the mandible is one of the most commonly fractured facial bones. Before the invention of the automobile, mandibular fractures were most often caused by assault or other blunt trauma to the jaw. However, vehicular accidents are now responsible for an equal share of the incidence of such injuries. (See also the eMedicine articles Facial Trauma, Mandibular Fractures [in the Plastic Surgery section] and Mandibular Condylar and Subcondylar Fractures, Mandibular Angle Fractures, Mandibular Body Fractures, and Mandible Fractures in Children [in the Otolaryngology and Facial Plastic Surgery section]. See also MR Imaging of the TMJ: A Pictorial Essay on Medscape.)
Radiologic evaluation is a standard component of the workup of a suspected mandibular fracture. With computed tomography (CT) scanning and panoramic imaging in addition to the basic mandibular radiographic study, a comprehensive evaluation and subsequent identification of all but the most subtle fractures can be achieved.
For excellent patient education resources, visit eMedicine's Back, Ribs, Neck, and Head Center, Breaks, Fractures, and Dislocations Center, and Teeth and Mouth Center. Also, see eMedicine's patient education articles Broken Jaw and Broken or Knocked-out Teeth.
Pathophysiology
The mandible is a ringlike structure. As with other ringlike bony structures, such as the zygomatic arch, fractures are usually multifocal (the pretzel rule). It is imperative, once a single mandibular fracture is identified, that a thorough search be undertaken to identify an accompanying fracture, both on the contralateral side and on the ipsilateral side. This is known as the ring or pretzel principle of the mandible: if 1 fracture is present, another should be sought. The average number of fractures per mandible is 1.5-1.8.
The temporomandibular joints (TMJs) provide limited protection from fractures due to centrally directed forces and rotational forces. These forces may also cause dislocation. In rare cases, a dislocated mandibular condyle can be driven centrally into the middle cranial fossa. (See also the eMedicine articles Dislocations, Mandible [in the Emergency Medicine section] and Temporomandibular Disorders [in the Neurology section].)
Trauma is not required to dislocate a mandibular condyle. Strong yawning or laughing may cause dislocations. After a dislocation, the mandibular condyle is seen anterior to the articular eminence of the temporal bone. If trauma is accompanied by hemotympanum, a fracture of the anterior wall of the external auditory canal (this is also the posterior wall of the TMJ) must be considered and assessed.
Gunshot wounds and other penetrating trauma can cause fractures of varying appearances, depending on the velocity and composition of the projectile. Higher-energy projectiles are associated with more fragmentation of bones upon impact (see Image 35).1
Frequency
United States
The mandible has been described as the fourth most common to the most common fractured bone in the face. Its rank climbs as the percentage of low-velocity trauma increases.
The 2 most common etiologies of mandibular fracture are direct trauma by a blunt object or a fist (low velocity) and by automobile accident (generally high velocity).2,3,4,5 Statistics vary depending on the socioeconomic status of a particular community, in which an area with more crime and poverty is associated with a higher percentage of assaults. Although injuries related to airbag deployment, including those to the mandible,6 do occur, the percentage of automobile-related injuries among all mandibular fractures has improved with the use of airbags and seatbelts.
About 30-45% of fractures are due to automobile accidents or assaults. Falls, sporting injuries, bike accidents, and work-related injuries all have single-digit prevalences. Pathologic fractures make up the small remainder of mandibular fractures.
The most common sites of mandibular fracture are at the body (21-40%), condyles (15-20%), and angle (20-31%). In addition, 10-15% affect the parasymphysis; 3-9%, the ramus; 3-5%, the alveolar ridge; and 1-2%, the coronoid process. Again, these numbers vary depending on the characteristics of a given community. Automobile accidents are associated with higher percentages of condylar fractures, whereas motorcycle accidents are frequently associated with symphyseal and parasymphyseal fractures. When the patient's history is of assault, body and angle fractures are more common.
International
The international rates of mandibular fractures also vary.
In a study by Mohammadi and Mohebbi, the authors conducted a retrospective study of 200 patients who had suffered maxillofacial injuries and who were seen at the Department of Otolaryngology and Head and Neck Surgery at Hazrat-e Rasoul Akram Hospital, Iran. Of the maxillofacial injuries that were evaluated, 36.2% were mandibular fractures; motor vehicle accidents were the most common etiology of these injuries.2
In a South African retrospective study of mandibular fractures, assault was the most common cause of such injuries (72.5%), followed by vehicular accidents (14.2%) and falls (8.8%).3
In another study comparing a US city with one in Turkey, assault was the most common cause of jaw fractures in the US city (53.7%) and motor vehicle accidents the most common etiology in the Turkish city (36.2%).4
Mortality/Morbidity
Mandibular fractures are not life threatening; however, the associated pathology often can be. In vehicular accidents in which the facial bones, including the mandible, are fractured, as many as 30% of patients have concomitant injuries of the cervical spine, skull base, or nervous system.
- With bilateral fractures of the mandibular body or parasymphysis, a retrodisplaced tongue can compromise the airway. The tongue can retract because the mandibular symphysis is the anterior attachment of the genioglossus, the geniohyoid, and the digastric muscles. Facial edema accompanying the fractures, loose teeth, or large amounts of intraoral bleeding can all compromise the airway as well.
- Mandibular fractures can have significant impact on the patient's quality of life. Besides the obvious interruption of normal mastication and occlusion, mandibular fractures can be associated with prolonged pain, trismus, and anesthesia/paresthesia to the lower lip and the skin overlying the chin (in cases of injury to the inferior alveolar nerve). Facial deformity is also an important concern.
- Ankylosis is a rare complication from intracapsular condylar fractures. This condition is likely due to intra-articular hemorrhage, which leads to abnormal fibrosis after overly late mobilization. Ankylosis is of most concern in children because it can lead to subsequent growth retardation of the affected condylar growth plate. Ankylosis can be diagnosed using thin-section direct coronal CT scan images with bone window settings.
Race
No significant racial differences in the fracture rate of mandibular fractures is known.
Sex
- The male-to-female incidence of mandibular fractures is approximately 3:1 in adults.3,4 It is 3:2 in children.
- Females tend to have more mandibular fractures at home (domestic violence) compared with men, who encounter more violence that results in fractures outside the home.
Age
- Children have a small percentage (approximately 5%) of mandibular fractures. Bicycle accidents are a common cause. Condylar fractures are more common than those in other anatomic locations. Children younger than 6 years are involved in only 1% of cases of mandibular fractures; the historical, physical, and imaging findings of the child's injury should be taken into consideration when determining whether the etiology of the fracture was due to an accident or due to abuse.5
- At the other side of the spectrum, a large percentage of mandibular fractures in patients older than 50 years are due to falls.
Anatomy
Mandibular fractures are primarily categorized by their anatomic location.7,8,9,10,11,12,13 These categories include condylar, coronoid, ramus, angle, parasymphysis, symphysis, alveolar, or combinations of these (see Image 1). Condylar fractures are further subgrouped as intracapsular (rare) or extracapsular.
The symphysis is the bone of the chin that extends back bilaterally to an imaginary line drawn vertically at the base of the canine teeth. The body is the bone between the angle and the symphysis. The ramus is defined as the bone between the coronoid, the condyle, and the mandibular angle. The alveolar ridge is the horseshoe of bone directly beneath the teeth.
The first incisor appears when an individual is approximately age 6 months, with a full complement of 20 teeth by age 2.5 years. Most patients have acquired all their permanent teeth at an average age of 18 years. The incisors are the first to appear, followed finally by the molars.
The inferior alveolar nerve, a branch of the lingular portion of the trigeminal nerve that provides sensation to the skin of the chin, traverses the mandible on the inner surface of the mandibular ramus. The nerve then travels through the mandibular canal and exits through the mental foramen on the outer surface of the mandibular body between the first and second premolar teeth.
The marginal mandibular branch of the mandibular nerve is rarely injured; the primary causes of damage to this branch of the nerve include cases of injury that occur near the condyles, rami, and angle.
Presentation
Even a minimal clinical history can be a valuable tool in the radiologic evaluation of the mandible; however, the history is often overlooked or unobtainable because of the status of the patient. When possible, the patient should be asked about a history of past fractures or any past trauma to the face. Mandibular fractures tend to heal slowly, and past fractures may be mistaken for acute injuries: lucency in the region of a fracture may be seen months after an injury. A history of any primary neoplasm, bony or collagenous disorders, or endocrine disorders is also important. Pathologic fractures make up a small proportion of mandibular fractures and should be particularly suspected in patients with a history of only minimal trauma.
Bilateral parasymphyseal or body fractures result in the separation of the mandibular symphysis from the rest of the mandible. These fractures should be recognized as soon as possible because the mandibular symphysis is the attachment of the genioglossus muscle (the largest muscle of the tongue), the geniohyoid muscle, and the digastric muscle. If the symphysis becomes a free fragment, the muscles of the tongue lose their anterior attachment and retract into the oral cavity, compromising the airway (see Image 2). This is the called the swallowed-tongue syndrome.
Preferred Examination
The radiologic workup of a suspected mandibular fracture initially depends on whether the patient presents with an isolated injury or with multi-injury trauma. If only an isolated mandibular fracture is suspected, radiographic evaluation should begin with the acquisition of a posteroanterior (PA) view (see Images 13, 29, 39, and 68), a Towne view (anteroposterior [AP] axial view) (see Images 3, 14, and 41), and bilateral oblique views (see Images 57-58). This is a typical, routine mandible series. If specialized equipment is available, a panoramic tomographic view ("Panorex view" [Panorex; Imaging Sciences International, Inc, Hatfield, Pa]) can also be obtained; this view shows the entire mandible in 1plane (see Images 9-10, 12, 24-26, 28, 34, 37, 42, 47, 55, and 66-67). If the results of these studies are equivocal or if more definition is requested, further specific views, such as the lateral, Waters (occipitomental view), periapical, or basal (submentovertex view), can be obtained. However, more often than not, CT scanning is performed.
A retrospective study of 42 patients showed that initial helical CT scans depicted 100% of mandibular fractures, whereas the initial panoramic imaging showed only 86% of such fractures that were eventually demonstrated.14 However, results from the same study also suggested that the bony detail of alveolar-ridge tooth-root fractures were better evaluated by using panoramic imaging.
For the CT scan examination, direct coronal and axial imaging should be attempted, depending on the patient's mobility. The direct coronal (or reverse coronal) series requires the patient's neck to be hyperextended, which is often not possible for patients who are in a spinal fixation collar. If direct coronal scans cannot be obtained, thinner axial sections (<3 mm) should be included in the protocol to allow for enhanced detail on the sagittal and coronal reconstructed images. As fast, thin-section, multidetector-row CT (MDCT) scanners become common, this consideration regarding the patient's mobility will be less of an issue, as motion artifact will be greatly reduced. With these scanners, reconstructed coronal imaging will likely become an accepted alternative to direct coronal imaging in most patients. CT scanning is most valuable in the assessment of suspected high-condylar fractures that are difficult to see on plain radiographs.
Patients with a suspected mandibular dislocation or limited excursion should undergo lateral imaging of the TMJs, with the acquisition of both open-mouth and closed-mouth views (see Images 58 and 61). This type of injury may also be examined by means of real-time fluoroscopy (see Image 60). Alternatively, open- and closed-mouth CT scanning may be performed.
Conversely, in patients with suspected mandibular fractures that are associated with major trauma or multiple injuries, radiography is usually limited to the acquisition of AP and lateral projections, immediately followed by thin-section CT scanning, with a section thickness of approximately 1.0-3.0 mm. Images should be reconstructed in both the coronal and sagittal planes.
Despite being visually impressive, 3-dimensional (3-D) reconstructed CT scan images are of questionable value in detecting fractures when compared with planar images. However, once a fracture is identified, 3-D images may be helpful in depicting the spatial relationships among fragments when planning for surgery and/or other treatment.15,16,17 Generally, 3-D images are not useful unless they are constructed from high-resolution thin-section CT scans.
Lastly, if a broken tooth or broken dentures are incidentally detected in the imaging studies, chest radiography should be performed to rule out the aspiration of teeth or other dental hardware.
Limitations of Techniques
The limitations of routine radiography include diminished sensitivity, poor technique, and lack of patient cooperation. Often, the proximal portion of the mandibular condyle is not visualized on any view. Sagittal fractures of the condyle are especially hard to identify. Oblique views are often acquired with overlap of the contralateral side (body, angle, and/or ramus) of the mandible. The symphyseal region is notoriously hard to evaluate because of overlap from the cervical spine. In this instance, a Waters or basal view may help in visualizing the symphysis.
The panoramic view (Panorex view) is even more affected by poor technique and lack of patient cooperation. Furthermore, the patient must be upright and hemodynamically stable for this examination. As such, panoramic imaging is not suitable in most trauma cases. In addition, many smaller emergency departments may not have the specialized equipment or the trained technologists that are needed for this modality. As on routine radiographs, panoramic views may not fully demonstrate the condyles, which can be obscured.
With CT scanning, mandibular fractures that are oriented in the same plane as the CT scan section can be obscured. For instance, a horizontal fracture through the mandibular body can be difficult to detect on axial CT images.
Motion artifact can hide even obvious fractures, which is even more true for reconstructed images. Dental work and fillings also create artifacts, but such artifacts are often not severe enough to interfere with the diagnosis.
A CT scan examination is relatively expensive compared with standard radiography. With any CT examination, the radiation dose to the patient is greater than that which is required for standard radiography. The typical effective dose-equivalent value of 1 head CT scan series is 200-400 millirems (mrems) compared with 10-20 mrems per plain radiograph. As with the Panorex equipment, there may sometimes be limited availability of CT scanners in small centers, especially after hours.
Differential Diagnoses
Other Problems to Be Considered
Ankylosis
Bony or collagenous disorders
Dislocations, Mandible
Endocrine disorders
Infection
Osteomyelitis (See also the eMedicine articles Osteomyelitis, Chronic [in the Radiology section] and Osteomyelitis [in the Emergency Medicine section].)
Pathologic fractures
Periapical abscess
Primary neoplasms
Temporomandibular Disorders
More on Mandible, Fractures |
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Further Reading
Keywords
broken jaw, jaw fracture, mandibular fracture, condylar fracture, coronoid fracture, ramus fracture, angle fracture, parasymphyseal fracture, symphyseal fracture, alveolar fracture, intracapsular fracture, extracapsular fracture, magnification sign, triple fracture
