You are in: eMedicine Specialties > Radiology > MUSCULOSKELETAL Mandible, FracturesArticle Last Updated: Nov 20, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: William C Soule, MD, Consulting Staff, Valley Radiology Medical Associates, Regional Medical Center of San Jose Office William C Soule is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, Radiological Society of North America, Society of Nuclear Medicine, and Society of Radiologists in Ultrasound Coauthor(s): Lee H Fisher, MD, Chief of Trauma Radiology, Department of Radiology, Santa Clara Valley Medical Center Editors: Giuseppe Guglielmi, MD, Associate Professor of Radiology, Department of Radiology, Scientific Institute Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Theodore E Keats, MD, Professor, Departments of Radiology and Orthopedics, University of Virginia School of Medicine; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington Author and Editor Disclosure Synonyms and related 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 INTRODUCTIONSection 2 of 11
  BackgroundGiven 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. PathophysiologyThe 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 FrequencyUnited StatesThe 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. InternationalThe international rates of mandibular fractures also vary. Mortality/MorbidityMandibular 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.
RaceNo significant racial differences in the fracture rate of mandibular fractures is known. Sex
Age
AnatomyMandibular 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. Clinical DetailsEven 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 ExaminationThe 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 TechniquesThe 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. DIFFERENTIALSSection 3 of 11
Other Problems to Be ConsideredAnkylosis RADIOGRAPHSection 4 of 11
FindingsThe nature of the trauma and the direction of the force that is applied often foretell the type of fracture injury. A patient who is hit on the side of his or her face often presents with an ipsilateral body fracture and a contralateral condylar fracture. An impact at the central symphysis (as with a head hitting a dashboard) can result in bilateral condylar fractures with a symphyseal or parasymphyseal fracture (the classic "triple fracture"). It is important to evaluate the adequacy of the radiographs. Besides adequate image quality, the absence of significant rotational malalignment of the PA, Towne, and panoramic views should be verified. On oblique views, the opposite mandible body should not be superimposed over the side that is being evaluated. Next, the cortical margin of all portions of the mandible should be traced. Often, only slight discontinuity of the cortex is seen. An indirect sign of mandibular fracture is any malocclusion or displacement of the teeth. In cases in which there is significant displacement of bone fragments, the identification of a fracture is an easy matter. However, because of the muscular attachments of the jaw, some fractures may be held in apposition. These are labeled the favorable fractures. Mandibular fractures can be labeled as horizontally or vertically favorable or unfavorable. In general, the muscular attachments of the mandible pull the anterior fragments posteriorly or inferiorly. Posterior fragments are generally pulled superiorly and medially. Edentulous patients often have greater displacement of bone fragments due to the lack of the structural stability of the mandibular alveolus and dentition. If a fracture occurs at the base of the condyle, the base is often pulled medially by the lateral pterygoid muscle up to 90º with the ramus. This finding is often accompanied by dislocation of the condyle from the TMJ. A dislocation should not be the interpretation in cases in which the condyle is only below the articular eminence. This finding is normal in the open-mouth position. In a true dislocation, the mandibular condyle is anterior to the articular eminence. In cases of bilateral condylar fractures with a symphyseal fracture (the triple fracture), the magnification sign may be seen, in which the lower jaw appears magnified compared with the upper jaw because bilateral lateral displacement of the mandibular bodies is present (See Image 23). The mandibular grooves should be traced bilaterally. Special attention should be paid to the condyles and symphysis because these areas often hide subtle fractures. Fractures of the alveolar ridge should be sought. An intraoral image may be required to more closely examine a tooth root. (Note: The intraoral film and other special dental views are often obtained in a dental surgery department rather than the typical radiology department.) Fractures may also be classified as greenstick (seen in children), simple, compound, comminuted, or pathologic. Compound fractures are those that communicate with the external surface of the wound. Alveolar fractures are included in this category because intraoral bacteria can infect the broken tooth and the underlying mandible (see Image 47). If a fracture is seen in a patient who has a history of only minimal trauma, the fracture site should be reevaluated for any evidence of an underlying bone tumor or periapical abscess. Degree of ConfidenceIf radiographic findings are still equivocal for a suspected fracture, repeat or additional views should be considered. If the new radiographic findings remain equivocal, a CT scan evaluation should be performed. False Positives/NegativesThe PA view is used to evaluate the entire mandible. However, the symphysis is often obscured by the cervical spine, and the condyles can be superimposed over the mastoid process and occipital bone (see Image 20). A Waters view or a basal view should be obtained to better evaluate the symphysis to negate the overlap of the cervical spin. The Towne view is primarily used to view the condyles, but again, bone overlap is common. Among all facial fractures, mandibular condyle fractures are the ones that are most commonly undiagnosed. Another important cause of false-negative results is not identifying any underlying bone pathology, such as a fracture resulting from a periapical abscess. This error is most likely due to the satisfaction-of-search phenomenon, but not identifying a pathologic lesion can lead to delayed healing, delayed treatment, and, possibly, later osteomyelitis. The normal mandibular groove should not be mistaken for a fracture (see Image 4). This structure is best seen on an oblique view (see Image 5). The normal appearance is 2 fine, parallel lines of cortical attenuation. Many structures can overlap on the plain radiographic series. These structures include vertebral bodies and soft tissues. In addition, air within the pharynx, bony ridges, and sinuses of the skull and/or face can also simulate fracture. The differentiation of these findings is the primary reason for the continued and increased use of CT scanning in the evaluation of questionable maxillofacial fractures. CT SCANSection 5 of 11
FindingsWith sagittal and coronal reconstructions, CT scans can depict all the portions of the mandible in 3 planes, but direct coronal views are always preferred. Besides identifying the fracture, it is easier to determine the degree of fragment displacement with CT scanning than with plain radiography. However, if the fracture is in the same plane as the CT scan section or if patient movement is excessive (this is most problematic with reconstructions), a fracture can be easily obscured. The CT scout image (computer-generated digital radiograph) should be evaluated because it may provide an approximation of the AP and lateral radiographic views. However, the scout image should not be considered a replacement for the lateral or AP images because the sensitivity of the scout image is much lower than that of the direct plain image. An internal study at the authors' institution (Santa Clara Valley Medical Center) was conducted to examine this issue. In the study, 400 trauma patients with mandibular fractures were retrospectively reexamined to determine if the CT scout images could have been used to predict an unknown mandibular fracture (before plain radiographs were obtained). The conclusion was that the scout images were not adequate as replacements for the AP and lateral plain images. This finding was partially based on the wide variations in the quality and positioning of the scout scans; more importantly, the finding was based on the low sensitivity of the scout images in the detection of fractures. However, looking at all of the images is still prudent; in the same internal study, most of the fractures that were suspected could be seen on the scout scan. Degree of ConfidenceCT scanning is the best method for detecting subtle or questionable fractures. CT scanning can also better elucidate hard-to-see fractures through the thin cortex of a pathologic lesion. False Positives/NegativesMotion artifact on reconstructed CT scan images can mimic a fracture. To reduce this artifact, the section thickness can be reduced and the sections can be overlapped. MRISection 6 of 11
FindingsWhereas CT scanning is used to evaluate the position of a condyle relative to the TMJ, MRI can be performed to evaluate the position and morphology of the cartilage of the TMJ.18, 19, 20 MRI is best for evaluating a torn meniscus or a displaced disk (internal derangement), but rarely is trauma the instigating factor for this study. As evaluated with MRI, TMJ pathology is most often degenerative in nature. This modality is also rarely used to evaluate for osteomyelitis that is secondary to mandibular fractures. ULTRASOUNDSection 7 of 11
FindingsEndoscopic ultrasonography offers an alternative to MRI for evaluating the TMJ,21 but ultrasonography is an invasive procedure, one that is usually performed with maxillofacial surgery.22, 23 NUCLEAR MEDICINESection 8 of 11
FindingsNuclear medicine studies are not performed for the evaluation of acute mandibular fractures. However, in rare cases, a bone scan may be used to evaluate healing at a fracture plane; plain radiographs may not show evidence of healing because of the slow radiographic appearance of bone repair. Infection and osteomyelitis after a fracture may be evaluated by means of triple-phase technetium-99m (99mTc) bone scanning. Concurrent plain radiography may also show soft-tissue swelling, periosteal thickening, and focal osteopenia. INTERVENTIONSection 9 of 11
In patients with multiple injuries due to an automobile accident, surgeons may not give mandibular fractures the highest priority, but early detection of such fractures is important because early reduction is associated with improved outcomes. Mandibular fractures can be treated by means of open or closed reduction. CT scanning is often required to identify intact bone before fixation with hardware proceeds. Delayed union, nonunion, and malunion are of concern in evaluating the response of mandibular fractures to treatment. Delayed union is the absence or delay of healing at the fracture plane along its normal timetable. After adequate treatment and immobilization are instituted, the fracture should resume normal healing. Nonunion is a lack of bony healing that persists without proper treatment and fixation. Subacutely, plain radiographs show no healing between bone fragments and, chronically, show rounding of the fracture segment edges. Malunion is the improper alignment of a healed fracture. However, in some cases, absolute prefracture alignment may not be necessary to restore full function. This complication may also be amenable to treatment with orthodontics. MULTIMEDIASection 10 of 11
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