eMedicine Specialties > Radiology > Musculoskeletal
Mandible, Fractures: Imaging
Updated: Nov 20, 2007
Radiography
Findings
The 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 90 º 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.
Again, the ring or pretzel principle of the mandible should always be remembered: if 1 fracture is present, look for another fracture.
Degree of Confidence
If 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/Negatives
The 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.
Computed Tomography
Findings
With 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 Confidence
CT 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/Negatives
Motion 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.
Magnetic Resonance Imaging
Findings
Whereas 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.
Ultrasonography
Findings
Endoscopic 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 Imaging
Findings
Nuclear 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 (99m Tc) bone scanning. Concurrent plain radiography may also show soft-tissue swelling, periosteal thickening, and focal osteopenia.
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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
