Published online August 14, 2003, 10.1148/rg.e14
(Radiographics. 2003;23:e14.)
© RSNA, 2003
Cross-sectional and Functional Imaging of the Temporomandibular Joint: Radiology, Pathology, and Basic Biomechanics of the Jaw1
Oliver J. Sommer, MD,
Felix Aigner, MD,
Ansgar Rudisch, MD,
Hannes Gruber, MD,
Helga Fritsch, MD,
Werner Millesi, MD and
Michael Stiskal, MD
1 From the Department of Radiology (O.J.S., M.S.) and Institute of Oral and Maxillofacial Surgery and Dentistry (W.M.), Hospital Lainz, Wolkersbergenstrasse 1, Vienna, Austria 1130; Institute of Anatomy, University Innsbruck, Austria (F.A., H.F.); and the Department of Radiology, University Hospital Innsbruck, Austria (A.R., H.G.). Presented as an educational exhibit at the 2002 RSNA scientific assembly. Received March 14, 2003, revision requested May 13, revision received and accepted July 8. Address correspondence to O.J.S. (e-mail: oliver.sommer@wienkav.at).
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Abstract
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The temporomandibular joint (TMJ) is a common site of complaint. Clicking sounds and pain are indicators of a frequent condition called internal derangement, most often affecting females. As a general term, internal derangement describes a structural abnormality within an articulation. The internal derangement of the TMJ is a specific term defined as an abnormal positional and functional relationship between the disk and articulating surfaces. Imaging of the joint is an important element in the diagnostic work-up. Trauma and inflammatory arthritis account for most of the other TMJ problems. A thorough understanding of joint anatomy and normal function is a prerequisite for perceiving abnormalities and making the correct diagnosis. The authors elucidate joint anatomy, correlating cadaveric specimen and anatomic slices with conventional and cross-sectional imaging studies. TMJ biomechanics are illustrated with schematics and animations, and an overview of imaging strategies and techniques is presented. Common abnormalities are described and illustrated, and a brief discussion of therapeutic options is included.
© RSNA, 2003
Index Terms: Joints, abnormalities, 244.14, 244.42, 244.78 • Joints, MR, 244.12141 • Joints, temporomandibular, 244.91
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Introduction
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Internal derangement and associated complications are the most common pathologic entities affecting the jaw. Conditions less frequently seen include trauma and inflammation (1–3). As a general term, internal derangement describes a structural abnormality within an articulation. The internal derangement of the temporomandibular joint (TMJ) is a specific term defined as an abnormal positional and functional relationship between the disk and articulating surfaces.
The prevalence of internal derangement varies greatly, depending on the population studied and the parameters used (4–11). Joint sounds are an associated frequent finding but do not represent a good epidemiologic tool, as they are found in only up to 35.8% of asymptomatic persons under the age of 18 on mouth opening or closing (4,6). There is a high rate of disk displacement in asymptomatic adolescents, and the frequency seems to increase with increasing age. Nebbe et al found normal joints in only 50% of boys and in 23%–29% of girls (6). The rest of the study population presented with different degrees of slight to full disk displacement with or without a change in morphology (6). In other studies, asymptomatic disk displacement was documented in approximately 30% of adolescents (7–9). On the other hand, 82% of patients presenting with pain and functional disturbance of their TMJ will have displaced disks when examined with magnetic resonance (MR) imaging (9).
The overall prevalence of symptomatic disk displacement or internal derangement may range between 20% and 30%, making them frequently encountered conditions (1,3). Trauma and arthritic disorders make up the major part of other pathologic intracapsular conditions affecting the jaw. Neoplasms and primary infectious arthritis are infrequently seen disorders and will not be discussed further, owing to their low prevalence.
MR imaging allows excellent depiction of TMJ anatomy and abnormalities because of its inherent tissue contrast and high resolution, given the use of dedicated surface coils (12–14). Concomitant imaging of the closed and open jaw allows additional functional and morphologic assessment and proper grading of disease processes of the articular disk. MR imaging is consequently the modality of choice in presumed internal derangement and inflammatory arthritis (2,3,12–14) and allows the clinician to apply therapeutic strategies optimally suited to the underlying abnormality.
Because of its availability and low cost, conventional radiography still functions as a prime diagnostic tool in many standard trauma facilities. It performs far inferiorly, however, to computed tomography (CT) in the evaluation and correct staging of traumatic injuries to the jaw and facial skeleton. The advent of multisection CT has revolutionized trauma radiology of the skull. Short scan times and reformatting techniques such as multiplanar reconstruction (MPR) provide invaluable advantages over single-section scanners. In almost all dedicated centers, CT now plays the key role in the assessment of jaw trauma and concomitant osseous injuries.
Just recently, early repair of injuries to the disk, its attachments, and the articular capsule that regularly accompany high-grade fractures of the articular process of the mandible has become an issue (15). If studies document an actual benefit of treating the soft-tissue structures of the joint after fixing of the fracture, MR imaging could become an important part of the radiologic work-up of jaw fractures.
Sonography may be a useful method in the assessment of the jaw in suspected cases of internal derangement or inflammation (16,17). There is, however, a scarcity of data in the literature, and as an operator-dependent modality, sonography entails a certain degree of interobserver variability. Therefore, sonography of the jaw will not be further discussed in this review. Arthrography—an invasive technique with associated complications (pain, infection, disk perforation, allergic reaction)–has been shown to be inferior to MR imaging with regard to diagnostic accuracy and has been replaced by MR imaging (17); it will not be described here.
We will provide a detailed description of joint anatomy and TMJ biomechanics, common abnormalities, and useful imaging techniques and therapeutic options.
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MR Imaging
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We perform TMJ imaging with a standardized protocol (Table 1). Injection of contrast material is not part of the scheme in our institutions. STIR sequences are a cost-effective alternative to fat-saturated contrast material–enhanced T1-weighted sequences and are included in our protocol.
Coronal and sagittal images of the TMJs are obtained after correction for the angulation of the condylar head (Fig 1) by using a set of standardized sequences and imaging parameters with a dual-coil technique (Table 1).
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Anatomy and Biomechanics
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The mandibular head, mandibular fossa, and articular eminence form the TMJ. A layer of hyaline cartilage covers the articulating cortical bone. An interposed fibrocartilaginous disk has a bow-tie-shaped biconcave morphology. The anterior and posterior ridges of the disk are termed anterior and posterior bands and are longer in the mediolateral than in the anteroposterior dimension. The smaller anterior band attaches to the articular eminence, condylar head, and joint capsule. The posterior band blends with highly vascularized, loose connective tissue, the bilaminar zone, and the capsule, the bilaminar zone residing in the retrodiskal space in the mandibular fossa and attaching to the condyle and temporal bone. Medially and laterally, the disk is firmly attached to the capsule and the condylar neck. Anteromedially, it is attached to the superior part of the pterygoid muscle. Infrequently, a water signal intensity can be noted in the central portion of the disk, resembling that of centrally hydrated vertebral disk (2,3,13,14,16–18) (Figs 2–5)
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Figure 2. Schematic of the temporomandibular disk in a sagittal projection. 1, Anterior band; 2, posterior band; 3, intermediate zone (inconstant central water signal intensity); 4, anterior attachment; 5, posterior attachment, or bilaminar zone.
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Figure 3a. (a) Schematic of the TMJ in a closed mouth position and sagittal projection and (b) sagittal thin section of a closed jaw. 1, Mandibular head; 2, articular eminence; 3, disk (3a, anterior band; 3b, intermediate zone; 3c, posterior band); 4, bilaminar zone; 5, lateral pterygoid muscle with interposed fat tissue (yellow in schematic) (5a, superior head; 5b, inferior head); 6, superior joint space; 7, inferior joint space.
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Figure 3b. (a) Schematic of the TMJ in a closed mouth position and sagittal projection and (b) sagittal thin section of a closed jaw. 1, Mandibular head; 2, articular eminence; 3, disk (3a, anterior band; 3b, intermediate zone; 3c, posterior band); 4, bilaminar zone; 5, lateral pterygoid muscle with interposed fat tissue (yellow in schematic) (5a, superior head; 5b, inferior head); 6, superior joint space; 7, inferior joint space.
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Figure 4a. (a) Schematic of the TMJ in a closed mouth position and coronal projection and (b) coronal thin section of a closed jaw. 1, Mandibular head; 2, articular fossa; 3, disk; 4, medial attachment; 5, lateral attachment; 6, superior joint space; 7, inferior joint space; 8, lateral pterygoid muscle.
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Figure 4b. (a) Schematic of the TMJ in a closed mouth position and coronal projection and (b) coronal thin section of a closed jaw. 1, Mandibular head; 2, articular fossa; 3, disk; 4, medial attachment; 5, lateral attachment; 6, superior joint space; 7, inferior joint space; 8, lateral pterygoid muscle.
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Figure 5. a, Sagittal and b, coronal MR images (770/27) of a normal TMJ with jaw in closed position. 1, Mandibular head; 2, articular fossa; 3, disk (3a, anterior band; 3b, intermediate zone; 3c, posterior band); 4, bilaminar zone; 5, lateral pterygoid muscle.
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In a physiologic joint, the disk is positioned between the mandibular head inferiorly and the articular eminence anteriorly and superiorly when the jaw is closed. The posterior band of the disk lies within 10° of the 12 o'clock position (3,19,20) (Fig 6, Movie 1). The medial and lateral corners of the disk align with the condylar borders and do not bulge laterally or medially (Fig 4, Movie 2).
When the jaw is opened, the disk slides into a position between the mandibular head and articular eminence (Figs 7, 8). The loose tissue of the bilaminar zone allows the remarkable range of motion of the disk. The attachments of the disk prevent luxation during opening. The disk does not move in the coronal plane when the joint is intact. For a schematic of the positional changes of the osseous and soft-tissue structures of the jaw during jaw opening, see Movie 3.
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Figure 7. Schematic of the TMJ in an open mouth position and sagittal projection. 1, Mandibular head; 2, articular eminence; 3, superior joint space; 4, inferior joint space; 5, disk (5a, anterior band; 5b, intermediate zone; 5c, posterior band); 6, bilaminar zone; 7, lateral pterygoid muscle with interposed fat tissue (yellow).
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Figure 8. a, Sagittal and b, coronal MR images (770/27) of a normal TMJ with the jaw in an open position. Note the bow-tie shape of the disk in the sagittal projection. 1, Mandibular head; 2, articular eminence; 3, disk (3a, anterior band; 3b, intermediate zone; 3c, posterior band) ; 4, bilaminar zone; 5, lateral pterygoid muscle.
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The TMJ is surrounded by a capsule, which consists of fibrous material, and a synovial lining. The capsule stretches from the edge of the mandibular fossa to the neck of the mandible, proximal to the pterygoid fovea, and envelops the articular eminence (Fig 9). The articular space is separated into superior diskotemporal and inferior diskomandibular spaces. A triangular lateral ligament acts as a strong lateral stabilizer and inhibits the posterior translation of the mandibular head (3,21).
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Figure 9. Photographs of anatomic TMJ specimens show (a) a lateral view in the closed position and (b) an anteroinferior view in the open position. The capsule is dissected laterally in a and anteriorly in b. The capsular attachments and their relationship to the disk can be appreciated. 1, Mandibular head; 2, articular eminence; 3, disk; 4, superior joint space; 5, joint capsule (5a, lateral; 5b, anterior; 5c, medial fibers).
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The muscles of mastication are responsible for the complex movement of the jaw. The temporal, medial pterygoid, and masseter muscles facilitate jaw closure. Mouth opening is effected by coordinated action of the lateral pterygoid, oral diaphragm, and suprahyoid muscles. The lateral pterygoid muscle and part of the fibers of the masseter and medial pterygoid muscles effect the anterior translation of the mandible.
The superior belly of the lateral pterygoid muscle originates from the greater sphenoid wing and inserts on the disk. Subsequently, the superior belly plays a key role in upholding the physiologic position of the disk as it pulls the disk forward when the jaw is opened, in a combined translation and rotation. The inferior head of the lateral pterygoid muscle stretches from the lateral lamina of the pterygoid process to the pterygoid fovea (21) (Fig 10). The medial pterygoid muslcle originates from the pterygoid fossa and inserts near the medial aspect of the mandibular angle (Fig 10).
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Figure 10a. (a, b) Photographs of anatomic TMJ specimens. (a) The joint capsule with the laterally reinforcing lateral ligament (1) and lateral pterygoid muscle (2) are shown in the lateral projection. The superior belly of the lateral pterygoid muscle inserts on the disk and the capsule (2A); the inferior part inserts on the mandibular neck (2B). (b) In the medial aspect, the mandibular ramus (1), the lateral pterygoid muscle (2), and the medial pterygoid muscle (3) are shown. (c) Coronal MR image (400/15) of the pterygoid muscles. The mandibular ramus (1), lateral pterygoid muscle (2), and medial pterygoid muscle (3) are shown.
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Figure 10b. (a, b) Photographs of anatomic TMJ specimens. (a) The joint capsule with the laterally reinforcing lateral ligament (1) and lateral pterygoid muscle (2) are shown in the lateral projection. The superior belly of the lateral pterygoid muscle inserts on the disk and the capsule (2A); the inferior part inserts on the mandibular neck (2B). (b) In the medial aspect, the mandibular ramus (1), the lateral pterygoid muscle (2), and the medial pterygoid muscle (3) are shown. (c) Coronal MR image (400/15) of the pterygoid muscles. The mandibular ramus (1), lateral pterygoid muscle (2), and medial pterygoid muscle (3) are shown.
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Figure 10c. (a, b) Photographs of anatomic TMJ specimens. (a) The joint capsule with the laterally reinforcing lateral ligament (1) and lateral pterygoid muscle (2) are shown in the lateral projection. The superior belly of the lateral pterygoid muscle inserts on the disk and the capsule (2A); the inferior part inserts on the mandibular neck (2B). (b) In the medial aspect, the mandibular ramus (1), the lateral pterygoid muscle (2), and the medial pterygoid muscle (3) are shown. (c) Coronal MR image (400/15) of the pterygoid muscles. The mandibular ramus (1), lateral pterygoid muscle (2), and medial pterygoid muscle (3) are shown.
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Internal Derangement
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As a general term, internal derangement describes a structural abnormality within an articulation. Internal derangement of the TMJ is a specific term defined as an abnormal positional and functional relationship between the disk and the articulating surfaces (2,3,13,22). Only 20%–30% of affected persons become symptomatic. Clicking sounds, pain, and functional restrictions (eg, "closed lock") are typical complaints. TMJs could be affected unilaterally, and subsequent deviations of the mandible can be observed during jaw movement. A subset of these symptomatic persons develop osteoarthritis, sometimes complicated by transient inflammation (1–11)
The cause of the disorder is unclear in most cases. Contrary to initial assumptions that it is a congenital disorder, it is now generally acknowledged to be an acquired degenerative process (11). Females are more prone to become symptomatic (eight times more often than males) after disk derangement, with complaints of pain, sounds, and functional impairment. A dedicated trial has been undertaken in an effort to link temporomandibular dysfunction with hormone levels in females without convincing evidence (23). Occlusal characteristics predisposing to the dysfunction have been cited in the literature (eg, open bite, other types of malocclusion, and certain parameters such as the range of mouth opening [4,10]). The pathophysiology of internal derangement stems from ligamentous laxity (3). Trauma and retrodiskal rents can contribute to development of the disorder.
Only a limited number of joints with displaced disks produce symptoms, and progression to severe, sometimes debilitating degenerative arthritis is noted in only a subset of these patients. Partial disk displacements may be associated with a lower prevalence of symptoms than full displacements (11).
Disk displacement may be uni- or multidirectional. Unidirectional anterior and multidirectional anterolateral and anteromedial displacements are the most common types (6,11). Unidirectional transverse displacements are rare, and posterior disk displacements are even more rare. Assessment of disk position necessitates both sagittal and coronal images. The jaw is first assessed in the closed position, and the exclusion or confirmation of disk displacement is performed with the jaw in this position.
Whether displaced disks relocate (disk recapture) to a physiologic position between the articular eminence and the mandibular condyle during jaw opening or stay displaced is an important issue in the grading and prognosis of the disorder. Joints that stay displaced are more likely to develop disk degeneration and rupture, as well as osteoarthritis.
Unidirectional Disk Displacement
Anterior and posterior disk displacements are diagnosed on sagittal images by using the position of the posterior band as a discriminator (Table 2). If the physiologic range of 10° ventral or dorsal to the 12 o'clock position is exceeded when the jaw is closed, the disk is displaced (Figs 11, 12). The coronal plane helps identify the medial and lateral attachments of the disk. In a physiologic joint, the medial and lateral borders of the disk do not extend beyond the border of the condylar head. Bulging characterizes disk displacement (Fig 13).
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Figure 12. Unidirectional complete anterior disk displacement. Sagittal MR image (2,800/15) of the TMJ with the jaw closed shows the disk deformity (arrow). Deformity of the condyle is also noted, due to osteoarthritic changes in the joint.
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Figure 13. Coronal MR images (2,800/15) of closed jaws. A slight medial disk displacement (arrow) is noted on the right side; a slight lateral displacement (arrow) is seen on the left side.
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Naturally, the sagittal plane is most useful for the exact identification of anterior and posterior dislocations, while the transverse plane is best for medial and lateral subluxations. Large displacements might be perceived in any plane.
A more detailed analysis may discriminate a partial from a complete disk displacement. In partial displacements (Fig 11), the disk continues to stay in contact with the regular articular surface of the condylar head, whereas this relationship is lost in completely displaced disks (Fig 12).
Multidirectional Disk Displacement
The identification and description of multidirectionally displaced disks is based on the combination of signs of unidirectional disk displacement. A careful interpretation of sagittal and coronal images allows a correct diagnosis (Fig 14, Movies 4, 5). A hint to the diagnosis of multidirectional disk displacement is the impossibility of identifying the complete disk in a single coronal or sagittal image.
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Figure 14a. Aneterolateral disk displacement. (a) Sagittal and (b) coronal MR images (2,800/15) of a pathologic TMJ with the jaw closed. In a, anterior displacement and deformity of the disk are noted. The arrow indicates the completely dislocated and deformed disk. For the whole sequence of images from medial to lateral, see Movie 4. In b, the lateral component of the anterolateral disk displacement can be easily identified. The disk (arrow) bulges laterally beyond the lateral condylar contour (indicated by the line). For the whole sequence of images, see Movie 5.
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Figure 14b. Aneterolateral disk displacement. (a) Sagittal and (b) coronal MR images (2,800/15) of a pathologic TMJ with the jaw closed. In a, anterior displacement and deformity of the disk are noted. The arrow indicates the completely dislocated and deformed disk. For the whole sequence of images from medial to lateral, see Movie 4. In b, the lateral component of the anterolateral disk displacement can be easily identified. The disk (arrow) bulges laterally beyond the lateral condylar contour (indicated by the line). For the whole sequence of images, see Movie 5.
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Recapture of Displaced Disks
When displaced disks regain their normal position during jaw opening, this is called recapture. Reduction is a synonymous term. A displaced disk sliding into a physiologic position between the articular eminence and condylar head during opening of the jaw indicates that attachments and capsule are less compromised than in joints in which the degree of subluxation does not change with jaw opening. The rupture of diskal attachments is on the more severe end of the spectrum of soft-tissue damage. Imaging of the open jaw allows further evaluation of the soft-tissue structures of the joint. It contributes to grading of the severity of internal derangement and helps identify patients at risk for developing sequelae such as degeneration, deformity, and reactive inflammation.
Unidirectionally displaced disks relocate (Movies 6, 7) or do not relocate (Movies 8, 9) in the plane of displacement. In multidirectional displacement, the disk may or may not relocate in one or both planes (Figs 15, 16).
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Figure 15. Unidirectional anterior disk displacement without recapture. Sagittal MR image (2,800/15) of a pathologic TMJ with the jaw open (same patient as Fig 12) shows that the anteriorly displaced disk (arrow) does not relocate. Deformity of the disk is noted.
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Figure 16a. Anterolateral disk displacement with complete recapture. (a) Coronal (left) and sagittal MR images (2,800/15) of a pathologic TMJ with the jaw in the closed position. The coronal image depicts the lateral bulging of the disk (arrow) beyond the condylar contour. The disk (arrow) is also depicted in the sagittal image.(b) MR image (2,800/15) of the same TMJ with the jaw in the open position. The disk (arrows) is in a normal position.
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Figure 16b. Anterolateral disk displacement with complete recapture. (a) Coronal (left) and sagittal MR images (2,800/15) of a pathologic TMJ with the jaw in the closed position. The coronal image depicts the lateral bulging of the disk (arrow) beyond the condylar contour. The disk (arrow) is also depicted in the sagittal image.(b) MR image (2,800/15) of the same TMJ with the jaw in the open position. The disk (arrows) is in a normal position.
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Sequelae of Internal Derangement
Disk displacement indicates damage to the attachments, capsule, and ligaments of the TMJ. The compromised structural integrity of the joint leads to functional disturbances. A process of degeneration to osteoarthritis may be initiated, although the degree and progression of this is as difficult to predict for the TMJ as for any other joint.
Synovitis, effusion, and bone marrow edema indicate active periods. Joint space narrowing, subchondral sclerosis and cyst formation, and contour irregularity and osteophyte formation characterize advanced stages of degeneration, reflected by neovascularity and remodeling of the disk (deformity, rupture, and signal intensity changes) (Fig 17).
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Figure 17. Anterior disk displacement with osteoarthritis. (a, b) Sagittal and (c, d) coronal STIR images (4,240/30, 150-msec inversion time) of a TMJ with the jaw in the closed position, in two different positions in the respective plane. Joint space narrowing, contour irregularity, and subchondral cyst are best depicted in the coronal images; bone marrow edema and synovial fluid are best seen in the sagittal images. 1, Condyle with areas of bone edema; 2, articular fossa; 3, displaced disk; 4, effusion; 5, cyst.
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Different grading systems have been developed to describe the degree of internal derangement and osteoarthritis (Tables 3, 4). The most simple system differentiates between partial ant total disk displacement on the basis of the position of the disk relative to the condylar head and articular eminence. Depending on their acceptance by physicians, theses schemes should be used as an adjunct to the diagnosis.
Treatment
Symptoms of internal derangement may resolve spontaneously; however, they may necessitate extensive medical therapy for severe and persistent pain and functional restriction. Treatment of asymptomatic disk displacement is not indicated.
Treatment of symptomatic internal derangement is based on a multimodal approach in which conservative and orthodontic procedures form the first line of treatment. A key element is patient reassurance that the condition has a mostly harmless course. The application of intraoral splints has two different therapeutic aims: correction of malocclusion with protrusive splints and alleviation of pressure exerted on soft-tissue structures of the TMJ with flat splints. Nonsteroidal antirheumatics help alleviate acute pain and inflammation.
In severe forms of internal derangement, especially in patients complaining of restricted movement, arthroscopic adhesioectomy is a good alternative (25). Disk plication, a surgical intervention with partial resection of the posterior band and reattachment of the disk, has a high success rate in patients with disk displacement without recapture. This procedure, however, can be performed only when there is no disk deformity (26,27).
In osteoarthritic joints with displaced and deformed disks without recapture, a total diskectomy procedure with implants has been tried (26,28). Because of complications (eg, arrosion and fracture of the temporal bone and implant displacement, inflammation, and foreign-body reaction), the technique is not a regular part of the therapeutic spectrum any longer (29,30).
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Trauma
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Car accidents and assaults are the cause of about 75% of mandibular fractures; falls and sporting accidents account for the rest. The type and location of mandibular fractures is related to the type of injury and the age of the patient, mirorring special developmental anatomic features of the mandible. The prevalence of condylar process fractures ranges between 25% and 50% of all mandibular fractures; falls and sporting accidents are the major contributors (31,32).
Fractures of the condylar process are classified as fractures of the condylar neck—low, medium, or high—and condylar head, which are classified as extracapsular or intracapsular. The distinction between high condylar neck and extracapsular condylar head fractures is somewhat arbitrary (Fig 18).
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Figure 18. Classification of condylar process fractures. Sites of low (L), medium (M), and high (H) condylar neck fractures and extracapsular and intracapsular condylar head fractures.
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Fractures are further subdivided into nondisplaced and displaced fractures. Owing to the traction of the lateral pterygoid muscle, fractures are typically displaced medially.
Evaluation of the type and grade of displacement of bony structures is essential for treatment planning. Various grading systems have been established, taking into account the angle between the mandibular head and ramus, contact of the fracture ends (especially the degree of contraction in the vertical plane, which influences occlusion), transverse displacement, and position of the fractured head with regard to the articular eminence and articular fossa (ie, the normal area of translation) (33,34).
Because of its low cost and availability, conventional radiography, particularly panoramic radiography, is frequently used as the first-line diagnostic tool in radiologic, orthopedic, and dental practise for trauma (Figs 19a). Osseous injuries and gross malalignments may well be diagnosed with this method. CT is the method of choice for assessment and grading of facial trauma. Multisection CT is an especially powerful technique, as it allows high-resolution multiplanar reconstructions (Figs 19b [Movie 10], 19c [Movie 11], 20). Concomitant osseous injuries such as factures of the zygomatic processes (Fig 20, Movie 12) and external auditory canal may be reliably determined.
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Figure 19a. Bilateral medially displaced fractures of the mandibular head with contraction. (a) Magnification of a lateral radiograph of the head. Fracture of the mandibular neck is noted (arrow). (b) Axial multisection CT (1.25-mm section thickness, table feed of 3.75 mm/sec, 25-cm FOV) provides an excellent overview of the fractures (arrows). For the whole sequence, see Movie 10. (c) Coronal reconstruction (2-mm reconstruction interval) of axial CT sections provides another excellent overview of fractures (arrows) and shows small fragments on the right. For the whole sequence, see Movie 11.
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Figure 19b. Bilateral medially displaced fractures of the mandibular head with contraction. (a) Magnification of a lateral radiograph of the head. Fracture of the mandibular neck is noted (arrow). (b) Axial multisection CT (1.25-mm section thickness, table feed of 3.75 mm/sec, 25-cm FOV) provides an excellent overview of the fractures (arrows). For the whole sequence, see Movie 10. (c) Coronal reconstruction (2-mm reconstruction interval) of axial CT sections provides another excellent overview of fractures (arrows) and shows small fragments on the right. For the whole sequence, see Movie 11.
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Figure 19c. Bilateral medially displaced fractures of the mandibular head with contraction. (a) Magnification of a lateral radiograph of the head. Fracture of the mandibular neck is noted (arrow). (b) Axial multisection CT (1.25-mm section thickness, table feed of 3.75 mm/sec, 25-cm FOV) provides an excellent overview of the fractures (arrows). For the whole sequence, see Movie 10. (c) Coronal reconstruction (2-mm reconstruction interval) of axial CT sections provides another excellent overview of fractures (arrows) and shows small fragments on the right. For the whole sequence, see Movie 11.
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Figure 20. Coronal reconstruction of axial multisection CT scans (1.25-mm section thickness, table feed of 3.75 mm/sec, 25-cm FOV, 2-mm reconstruction interval). Nondisplaced fracture of the right zygomatic process (1), vertical condylar head fracture on the right (2) and comminuted, displaced condylar head fracture (3) on the left. For the whole sequence, see Movie 12.
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Evaluation of the disk, its attachments, and the articular capsule has become an issue when comparing the benefits of conservative and surgical treatment approaches for condylar process fractures. To our knowledge, most of the studies comparing different surgical and nonsurgical therapeutic approaches use parameters such as angulation, vertical compression, and contact between fracture ends. The type and severity of damage to the soft-tissue structures of the joint (ie, disk, attachments, and capsule) may well influence the efficacy of the therapeutic approach. Therefore, pretherapeutic MR imaging may play a role in future comparative therapeutic studies and, probably, treatment decisions (15). Whereas the disk remains attached to the condylar head fragment in most nondislocated and low-grade fractures and regains its physiologic position after recapture, the degree of soft-tissue damage increases with dislocated and severe high-grade fractures (15,35,36).
MR imaging can help identify posttraumatic disk dislocation and rupture and injury to attachments, capsule, cartilage, and ligaments in the pretherapeutic evaluation. Immediate arthroscopic repair, however, is currently not part of any therapeutic scheme and is reserved for those with late sequelae such as adhesions, symptomatic internal derangement, and osteoarthritis.
Correct fracture union and reduction, preservation of normal dental occlusion, normal joint function, and a good cosmetic result are major treatment goals. Functional disturbances, pain, ankylosis, and early osteoarthritis are negative consequences of inadequate fracture healing. Closed or open reduction techniques are applied depending on the type and severity of the injury and age and health status of the patient (3,31,32,37). In general, a conservative approach is favored. Intraoral appliances and physical therapy with early activation of the joint are beneficial in most cases of nondisplaced fractures. With mild and moderate displacement, immobilization with intermaxillary fixation (rubber bands on vestibular screws) for 2–3 weeks is the method of choice, provided that sufficient occlusal contact is present. To prevent intraarticular compression and to increase the vertical distance between compressed fracture ends, distraction and protrusion devices (eg, interocclusal splints) are used.
In cases of severe dislocation, open reduction and internal fixation are recommended. In our institutions a 30%–50% angulation, vertical compression of 1–2 cm and lack of contact between fracture ends are indications for open reduction. These indications, however, are not uniformly accepted at all institutions, and the issue is contoversial in the literature. In low and medium condylar neck fracures, osteosynthesis (with miniplates and screws) is performed via an intraoral approach (Fig 21). In high condylar neck fractures and fractures of the condylar head, an extraoral approach is used. Except for titanium screws, biodegradable and resorbable material may be used.
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Figure 21a. Bilateral low condylar neck factures; nondisplaced fracture on the right, laterally displaced fracture on the left (arrows). Panoramic radiographs (a) before and (b) after osteosynthesis with plates.
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Figure 21b. Bilateral low condylar neck factures; nondisplaced fracture on the right, laterally displaced fracture on the left (arrows). Panoramic radiographs (a) before and (b) after osteosynthesis with plates.
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The treatment of choice for childhood fratures is the conservative approach, as children have a high potential for remodeling of the condylar process owing to their active center of growth. To avoid misalignment and late sequelae such as ankylosis and osteoarthritis, open reduction is performed in cases of severe dislocation even in children.
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Inflammation
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As a synovia-lined joint, the TMJ may be affected by synovial arthropathies, predominantly rheumatoid arthritis. The jaw may rarely be involved in gout, psoriatic arthritis, ankylosing spondylitis, systemic lupus erythematosus, juvenile chronic arthritis, and calcium pyrophosphate dihydrate deposition (3).
As the pathophysiologic process is identical in all these disorders, no distinction can be made between different forms of synovial arthropathy with MR imaging of the TMJ. The spectrum of classic radiologic symptoms ranges from synovitis with tissue swelling, edema, and effusion to joint space narrowing, cartilage destruction, erosions, and marrow edema. As in other joints, formation of granulation tissue and pannus typically occurs in the "bare areas" near the capsular insertion.
Because of the high vascularity and loose tissue structure, edema in joint inflammation can be identified in the bilaminar zone early in the process (Fig 22). T2-weighted inversion-recovery techniques with fat saturation are sensitive in this respect, and STIR imaging is optimally suited for this indication (Fig 23, Movie 13). Contrast-enhanced T1-weighted spin-echo sequences do not contribute much in the way of additional information. Enhancement, by the way, is not specific and does not help in the differential diagnosis between primary inflammation and synovitis secondary to osteoarthritis (3,37).
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Figure 22. Inflamed TMJ in rheumatoid arthritis. Sagittal T1-weighted (400/15) spin-echo MR images a, before and b, after intravenous contrast material infusion show slight enhancement of the bilaminar zone (arrow).
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Figure 23. Sagittal STIR image (4,240/30, 150-msec inversion time) of an inflamed TMJ in patient with rheumatoid arthritis. The synovitis and inflammation of the surrounding tissue can be easily detected because of the increased water content (1). A small volume of intracapsular fluid in the superior joint space is visible (2). In this patient, the partial anterior disk displacement (3) did not cause any symptoms. For the whole sequence from medial to lateral, see Movie 13.
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Conclusions
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The integrity of a complex joint such as that of the jaw is the result of a balanced interaction of soft tissue and bony structures. Despite its daily exposure to wear and tear, severe changes in the TMJ are rare. Trauma, internal derangement with possible sequelae (osteoarthritis), and inflammation are the most common forms of pathologic conditions. Affected patients complain of clicking sounds during jaw movement, pain, and functional disturbance. Symptoms may be unilateral or bilateral.
The general radiologist is frequently challenged to manage the diagnostic pathway and to provide a good basis for planning the proper therapeutic strategy. Conventional radiography helps identify gross bone abnormalities. CT, especially multisection CT, is the modality of choice for assessing the TMJ. Soft-tissue anatomy is best depicted with MR imaging and a standardized imaging protocol. Because of the operator dependence and limited FOV of sonography and the invasiveness and propensity for severe complications of arthrography, these modalities are not part of a routine work-up of the TMJ.
The ability to formulate an optimal diagnosis is based on a thorough understanding of the normal anatomy and physiology of structures of the jaw. Knowledge of indications, radiologic diagnostic strategies, and basic therapeutic options can be enhanced rapidly and clearly with use of a concise teaching module.
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Footnotes
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Abbreviations: FOV = field of view,
STIR = short-inversion-time inversion recovery,
TMJ = temporomandibular joint
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References
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Abstract
Introduction
