Diagnostic Imaging of the Temporomandibular Joint

Panoramic Projection

The panoramic projection is often included as part of the examination because it provides an overall view of the teeth and jaws, provides a means of comparing left and right sides of the mandible, and serves as a screening projection to identify odontogenic diseases and other disorders that may be the source of TMJ symptoms. Some panoramic machines have specific TMJ programs, but these are of limited usefulness because of thick image layers and the oblique, distorted view of the joint they provide, which severely limits image quality. Gross osseous changes in the condyles may be identified, such as asymmetries, extensive erosions, large osteophytes, tumors or fractures (Fig. 26-6). However, no information about condylar position or function is provided because the mandible is partly opened and protruded when this radiograph is exposed. Also, mild osseous changes may be obscured, and only marked changes in articular eminence morphology can be seen as a result of superimposition by the skull base and zygomatic arch. For these reasons, the panoramic view should not be used as the sole imaging modality and should be supplemented.

Plain Film Imaging Modalities

Plain films, usually consisting of a combination of transcranial, transpharyngeal (Parma), transorbital, and submentovertex (basal) projections allow visualization of the TMJs in various planes (Fig. 26-7). Transcranial and transpharyngeal projections provide lateral views. The transcranial view is taken in the closed and open mouth positions and depicts the lateral aspect of the TMJ, whereas the transpharyngeal projection is taken in the mouth open position only and depicts the medial aspect of the condyle. The transorbital projection is taken in the open or protruded position and depicts the entire medial-lateral aspect of the condyle in the frontal plane and is very useful in detecting condylar neck fractures. A submentovertex projection provides a view of the skull base and condyles in the horizontal plane; it is often used to determine the angulation of the long axes of the condylar heads for corrected tomography. These imaging techniques are gradually being replaced with more advanced imaging such as cone-beam computed tomography (CT).

Conventional Tomography

Tomography is a radiographic technique that produces multiple thin image slices, permitting visualization of the osseous structures essentially free of superimpositions of overlapping structures (see Chapter 14). This technique can provide multiple image slices at right angles through the joint, depicting true condylar position and revealing osseous changes. Conventional tomography is gradually being replaced by cone-beam CT (CBCT) as the imaging technique of choice for assessing the osseous structures of the TMJ. Tomographs typically are exposed in the sagittal (lateral) plane, corrected to the condylar long axis, with several image slices in the closed (maximal intercuspation) position and usually only one image in the maximal open position. It is desirable to supplement the sagittal images with coronal (frontal) tomographs (Fig. 26-8), particularly when morphologic abnormalities or erosive changes of the condylar head are suspected. The entire condylar head is visible in the mediolateral plane.

Computed Tomography

CT provides more information about the three-dimensional shape and internal structure of the osseous components of the joint by providing detailed image slices and three-dimensional images. There are two CT devices available, conventional CT (sometimes referred to as medical CT, see Chapter 14) and CBCT. Both modalities can give excellent images of the osseous structures, but only conventional CT provides images of the surrounding soft tissues; however, this is only required in a minimal number of specific situations. CBCT has the advantage of reduced patient dose compared with medical CT and is likely to replace conventional tomography. In CBCT the patient is usually scanned in the closed position and low-resolution scans can be done in the open or other positions (see Chapter 13). Data from the axial slices can be manipulated to produce (reformat) corrected lateral and frontal images of the TMJs (see Fig. 26-3). Panoramic and three-dimensional reformatted images also can be produced. These are useful for assessing osseous deformities of the jaws or surrounding structures. Conventional and CBCT cannot produce accurate images of the articular disk.

CT is also useful for determining the presence and extent of ankylosis and neoplasms and the degree of bone involvement in some arthritides, for imaging complex fractures, and for evaluating complications from the use of polytetrafluoroethylene or silicon sheet implants, such as erosions into the middle cranial fossa and heterotopic bone growth.

Magnetic Resonance Imaging

MRI uses a magnetic field and radiofrequency pulses rather than ionizing radiation to produce multiple digital image slices (see Chapter 14). Because MRI can provide superb images of soft tissues, this technique can be used for imaging the articular disk. MRI allows construction of images in the sagittal and coronal planes without repositioning the patient (Fig. 26-9). These images usually are acquired in open and closed mandibular positions with use of surface coils to improve image resolution. Sagittal slices should be oriented perpendicular to the condylar long axis. The examinations usually are performed with use of T1-weighted, proton-weighted, or T2-weighted pulse sequences. T1-weighted and proton-weighted images best demonstrate osseous and diskal tissues, whereas T2-weighted images demonstrate inflammation and joint effusion. Motion MRI studies during opening and closing can be obtained by having the patient open in a series of stepped distances and with use of rapid image acquisition (“fast scan”) techniques.

MRI is contraindicated in patients who are pregnant or who have pacemakers, intracranial vascular clips, or metal particles in vital structures. Some patients may not be able to tolerate the procedure because of claustrophobia or an inability to remain motionless.

Definition

Condylar hyperplasia is a developmental abnormality that results in enlargement and occasionally deformity of the condylar head; this may have a secondary effect on the mandibular fossa as it remodels to accommodate the abnormal condyle. Some proposed etiologic factors include hormonal influences, trauma, infection, heredity, intrauterine factors, and hypervascularity. The mechanism may be overactive cartilage or persistent cartilaginous rests, which increases the thickness of the entire cartilaginous and precartilaginous layers. This condition usually is unilateral and may be accompanied by varying degrees of hyperplasia of the ipsilateral mandible.

Clinical Features

Condylar hyperplasia is more common in males, and it usually is discovered before the age of 20 years. The condition is self-limiting and tends to arrest with termination of skeletal growth, although in a small number of cases continued growth and adult onset have been reported. The condition may progress slowly or rapidly. Patients have a mandibular asymmetry that varies in severity, depending on the degree of condylar enlargement. The chin may be deviated to the unaffected side, or it may remain unchanged but with an increase in the vertical dimension of the ramus, mandibular body, or alveolar process of the affected side. As a result of this growth pattern, patients may have a posterior open bite on the affected side. Patients may also have symptoms related to TMJ dysfunction and may complain of limited or deviated mandibular opening, or both, caused by restricted mobility of the enlarged condyle.

Radiographic Features

The condyle may appear relatively normal but symmetrically enlarged, or it may be altered in shape (e.g., conical, spherical, elongated, lobulated) or irregular in outline. It may be more radiopaque because of the additional bone present. A morphologic variation manifesting as elongation of the condylar head and neck with a compensating forward bend, forming an inverted L, may be seen. Also, the condylar neck may be elongated and thickened and may bend laterally when viewed in the coronal (anteroposterior) plane (Fig. 26-10). The cortical thickness and trabecular pattern of the enlarged condyle usually are normal, which helps to distinguish this condition from a condylar neoplasm. The glenoid fossa may be enlarged, usually at the expense of the posterior slope of the articular eminence. The ramus and mandibular body on the affected side also may be enlarged, resulting in a characteristic depression of the inferior mandibular border at the midline, where the enlarged side joins the contralateral normal mandible. The affected ramus may have increased vertical depth and may be thicker in the anteroposterior dimension.

Differential Diagnosis

A condylar tumor, most notably an osteochondroma, is included in the differential diagnosis. An osteochondroma usually is irregular in shape compared with a hyperplastic condyle. Surface irregularities and continued growth after cessation of skeletal growth should increase suspicion of this tumor. Occasionally a condylar osteoma or large osteophyte that occurs in chronic degenerative joint disease may simulate condylar hyperplasia.

Treatment

Treatment consists of orthodontics combined with orthognathic surgery and it may be initiated before condylar growth is complete to avoid functional problems (mastication and speech) and worsening esthetic disfigurement. If treatment is delayed, severe mandibular deformation and compensatory changes in the maxilla, dentoalveolar structures, and associated soft tissues may result, which may compromise treatment outcome. On the other hand, treatment before condylar growth is completed may result in relapse of occlusal and esthetic problems. Cessation of growth of the condyle may be determined with technetium bone scans.

Definition

Condylar hypoplasia is failure of the condyle to attain normal size because of congenital and developmental abnormalities or acquired diseases that affect condylar growth. The condyle is small, but condylar morphology usually is normal (Fig. 26-11). The condition may be inherited or may appear spontaneously. Some cases have been attributed to early injury or injury to the articular cartilage by birth trauma or intra-articular inflammatory lesions.

Clinical Features

Condylar hypoplasia usually is a component of a mandibular growth deficiency and therefore is often associated with an underdeveloped ramus and (occasionally) mandibular body. Congenital abnormalities may be unilateral or bilateral and usually are a manifestation of a more generalized condition (e.g., micrognathia, Treacher Collins syndrome); they also may be associated with congenital defects of the ear and zygomatic arch. Developmental abnormalities that manifest during growth usually are unilateral. Acquired abnormalities are the result of damage during the growth period from sources, such as therapeutic radiation or infection, that diminish or prevent further condylar growth and development. Patients with condylar hypoplasia have mandibular asymmetry and may have symptoms of TMJ dysfunction. The chin commonly is deviated to the affected side, and the mandible deviates to the affected side during mandibular opening. Degenerative joint disease is a common long-term sequela.

Radiographic Features

The condyle may be normal in shape and structure but is diminished in size, and the mandibular fossa also is proportionally small (Fig. 26-12). The condylar neck and coronoid process usually are very slender and are shortened or elongated in some cases. The posterior border of the ramus and condylar neck may have a dorsal (posterior) inclination. The ramus and mandibular body on the affected side may also be small, resulting in a mandibular asymmetry and occasional dental crowding, depending on the severity of mandibular underdevelopment. The antegonial notch is deepened. The associated mandibular hypoplasia is more pronounced if the effect takes place early in life.

Differential Diagnosis

Condylar destruction from juvenile rheumatoid arthritis may appear similar to that of hypoplasia. A survey of other joints or testing for rheumatoid factor may be helpful. Changes in condylar morphology in severe degenerative joint disease or other arthritic conditions may have a similar appearance, although arthritic disease does not cause mandibular hypoplasia of the affected side unless it occurs during growth, and other signs of arthritis are usually visible in the affected joint.

Treatment

Orthognathic surgery, bone grafts, and orthodontic therapy may be required.

Synonyms

Boering’s arthrosis and arthrosis deformans juvenilis

Definition

Juvenile arthrosis, a condylar growth disturbance first described by Boering, manifests as hypoplasia and characteristic morphologic abnormalities. This condition may be a form of condylar hypoplasia but is thought to differ in that the affected condyle at one time was normal, becoming abnormal during growth. Juvenile arthrosis may be unilateral or bilateral, and it predisposes the TMJ to secondary degenerative changes.

Clinical Features

Juvenile arthrosis affects children and adolescents during the period of mandibular growth. It is more common in females. It may be an incidental finding in a panoramic projection, or the patient may have mandibular asymmetry, signs and symptoms of TMJ dysfunction, or both.

Radiographic Features

The condylar head develops a characteristic “toadstool” appearance, with marked flattening and apparent elongation of the articulating condylar surface and dorsal (posterior) inclination of the condyle and neck. The condylar neck is shortened or even absent in some cases, with the condyle resting on the upper margin of the ramus (Fig. 26-13). The articulating surface of the temporal component often is flattened. Progressive shortening of the ramus occurs on the affected side, and the antegonial notch may be deepened, indicating mandibular hypoplasia. In long-standing cases, superimposed degenerative changes may be present.

Differential Diagnosis

The radiographic appearance of juvenile arthrosis may be very similar to, and in some cases is indistinguishable from, developmental hypoplasia of the condyle. Destruction of the anterior aspect of the condylar head from rheumatoid arthritis and severe degenerative joint disease or severe condylar degeneration after orthognathic surgery or joint surgery also may simulate juvenile arthrosis.

Treatment

Orthognathic surgery and orthodontic therapy may be required to correct the mandibular asymmetry. Caution should be exercised in undertaking orthodontic therapy because stress on the joint may result in further degeneration and orthodontic relapse.

Definition

Coronoid process hyperplasia may be acquired or developmental, resulting in elongation of the coronoid process. In the developmental variant, the condition usually is bilateral. Acquired types may be unilateral or bilateral and usually are a response to restricted condylar movement caused by abnormalities such as ankylosis.

Clinical Features

Bilateral developmental coronoid hyperplasia is more common in males, often commencing at the onset of puberty, although the condition was reported in a 3-year-old child. Patients complain of a progressive inability to open the mouth and may have an apparent closed lock. The condition is painless.

Radiographic Features

Coronoid hyperplasia is best seen in panoramic, Waters, and lateral tomographic views and on CT scans. The coronoid processes are elongated, and the tips extend at least 1 cm above the inferior rim of the zygomatic arch (Fig. 26-14). As a result, the coronoid processes may impinge on the medial surface of the zygomatic arch during opening, restricting condylar translation. This can be confirmed by using CT imaging (Fig. 26-15). The coronoid processes may have a large but normal shape or may curve anteriorly and may appear very radiopaque. The posterior surface of the zygomatic process of the maxilla may be remodeled to accommodate the enlarged coronoid process during function. The radiographic appearance of the TMJs usually is normal.

Differential Diagnosis

Unilateral cases should be differentiated from a tumor of the coronoid process such as an osteochondroma or osteoma. Unlike coronoid hyperplasia, tumors usually have an irregular shape. The differential diagnosis also includes any cause of inability to open, such as soft tissue abnormalities and ankylosis, emphasizing the importance of including the coronoid process in images of the TMJs. An axial CT image with the patient in a wide open position is useful in establishing coronoid interference to opening.

Treatment

Treatment consists of surgical removal of the coronoid process and postoperative physiotherapy. Regrowth of the coronoid process after surgery has been reported.

Definition

A bifid condyle has a vertical depression, notch, or deep cleft in the center of the condylar head, seen in the frontal or sagittal plane, or actual duplication of the condyle, resulting in the appearance of a “double” or “bifid” condylar head. This condition is rare and is more often unilateral, although it may be bilateral. It may result from an obstructed blood supply or other embryopathy, although a traumatic cause has been postulated as a result of a longitudinal linear fracture of the condyle.

Clinical Features

Bifid condyle usually is an incidental finding in panoramic views or anteroposterior projections. Some patients have signs and symptoms of temporomandibular dysfunction, including joint noises and pain.

Radiographic Features

A depression or notch is present on the superior condylar surface, giving the anteroposterior silhouette a heart shape; in more severe cases a duplicate condylar head is present in the mediolateral plane (Fig. 26-16). The orientation of the bifid condyle may be anteroposterior or mediolateral. The mandibular fossa may remodel to accommodate the altered condylar morphology.

Differential Diagnosis

A slight medial depression on the superior condylar surface may be considered a normal variation; the point at which the depth of the depression signifies a bifid condyle is unclear. The differential diagnosis also includes a vertical fracture through the condylar head.

Treatment

Treatment is not indicated unless pain or functional impairment is present.

Definition

An internal derangement is an abnormality in the position and sometimes the morphology of the articular disk that may interfere with normal function. The disk most often is displaced in an anterior direction, but it may be displaced anteromedially, medially, or anterolaterally. Lateral and posterior displacements are extremely rare. Some hypothesize that disk displacements may be considered a normal variation on the basis of the frequency of this finding in asymptomatic patients. The cause of internal derangements is unknown, although parafunction, jaw injuries (e.g., direct trauma), whiplash injury, and forced opening beyond the normal range have been implicated.

Internal derangements can be diagnosed by MRI. In some instances the disk may resume a normal position with respect to the condyle (called reduction of the disk) during mandibular opening; when the disk remains displaced throughout the entire range of mandibular movement, the term nonreduction is used (Fig. 26-17). A long-standing displaced disk may become deformed, losing its normal biconcave shape, and it may become thickened and fibrotic. Possible complications are degenerative joint disease and perforation through the disk or (more commonly) the posterior attachment.

Clinical Features

Disk displacement has been found both in symptomatic patients and in healthy volunteers, suggesting that it may be a normal variant and not necessarily a predisposing factor in TMJ dysfunction. It is not known why some disks remain displaced or why symptoms of pain and dysfunction are not found in all affected patients. Symptomatic patients may have a decreased range of mandibular motion. Internal derangements can be unilateral or bilateral; unilateral cases may manifest clinically as mandibular deviation to the affected side on opening. Joint noises are common and may manifest as a click as the disk reduces to a normal position during mandibular opening and occasionally as a softer click as the disk becomes displaced again during mandibular closing. Noises may be absent in long-term displaced, nonreducing disks, or crepitus may be heard. Patients may complain of pain in the preauricular region or headaches and may have episodes of closed or open locking of the joint. Patients may have to manipulate the mandible to open it fully past an apparent closed lock by applying medially directed pressure to the affected joint or mandible with the hand.

Radiographic Features

The disk cannot be visualized with conventional radiography or tomography; MRI is the technique of choice. Although a retruded condylar position has been associated with disk displacement, condylar position in maximal intercuspation is not a reliable indicator of disk displacement. Likewise, diminished range of motion at maximal opening is not a reliable indication of a nonreducing disk. In MRI the normal disk has a low signal intensity (is dark between bone and muscle), and the signal intensity of the bilaminar zone is usually higher (i.e., lighter). In the closed-mouth position, the normal disk is positioned with the posterior band directly superior to the condylar head and the thin intermediate part between the anterosuperior surface of the condyle and the posteroinferior surface of the articular eminence (see Fig. 26-9). It is important to note that in all positions of mouth opening the thin intermediate part remains the articulating surface of the disk between condyle and articular eminence.

Disk Displacement

Identifying the disk may be difficult in cases of gross deformation of the disk and other soft tissue components. Anterior displacement is the most common disk displacement. When the mandible is in maximal intercuspation, partial or full anterior disk displacement is indicated by anterior location of the posterior band of the disk from the normal position, which is directly superior to the condylar head. An indication of anterior displacement is positioning of the posterior band forward so that it sits between the anterosuperior surface of the condyle and the eminence (Fig. 26-18). However, correct identification of the posterior band may be impossible if the tissue signal of the bilaminar zone approximates the posterior band, which occurs in chronic disk displacements. Therefore it is also important to evaluate the position of the thin intermediate part of the disk, which should be adjacent to the anterosuperior part of the condyle. Anteromedial displacement is indicated in sagittal image slices when the disk is in a normal position in the medial images of the joint but anteriorly positioned in the lateral images of the same joint. Medial or lateral displacement is indicated in MRI coronal images when the body of the disk is positioned at the medial aspect of the condyle (Fig. 26-18). Posterior disk displacement is rare.

Disk Reduction and Nonreduction

During mouth opening, an anteriorly displaced disk may reduce to a normal relationship with the condylar head during any part of the opening movement. In motion studies, this is usually a rapid posterior movement of the disk and it is often accompanied by an audible click. This is referred to as disk reduction and can be diagnosed if the disk is in a normal position in the open mouth magnetic resonance images (see Fig. 26-18).

If the disk remains anteriorly displaced (nonreduction) on opening, it may bend or deform as the condyle pushes against it (Fig. 26-19). If the disk remains displaced, it will undergo permanent deformation, losing its biconcave shape. The nonreduced disk is readily seen on MRI scans, although fibrotic changes of the bilaminar zone may alter its tissue signal to approximate the signal of the disk and thus make identification of the disk itself difficult. In such cases the disk may be erroneously interpreted as occupying a normal position at maximal opening.

Perforation and Deformities

Perforations between the superior and inferior joint spaces most commonly occur in the retrodiskal tissue, just behind the posterior band of the disk (Fig. 26-20, C) and can be detected in arthrographic investigations but are not reliably detected with MRI. MRI can indicate alteration in the normal biconcave outline of the disk, which may vary from enlargement of the posterior band to a bilinear or biconvex disk outline. Disk deformities may be accompanied by changes in its signal intensity, sometimes an increase in signal. Changes to the condyle and temporal component of the joint consistent with degenerative joint disease often accompany cases with long-standing displaced disks (Fig. 26-20).

Fibrous Adhesions and Effusion

Fibrous adhesions are masses of fibrous tissue or scar tissue that form in the joint space, particularly after TMJ surgery. Adhesions are best identified with arthrography by resistance to injection of contrast agent or they may be detected in MRI studies as tissue with low signal intensity. The pressure of injected contrast agent may tear some of these adhesions, resulting in increased joint mobility after the procedure. Joint effusion (fluid in the joint) is considered to be an early change that may precede degenerative joint disease. MRI can detect joint effusion, which presents as an area of high-signal intensity in the joint spaces in T2-weighted images (see Fig. 26-19).

Definition

Remodeling is an adaptive response of cartilage and osseous tissue to forces applied to the joint that may be excessive, resulting in alteration of the shape of the condyle and articular eminence. This adaptive response may result in flattening of curved joint surfaces, which effectively distributes forces over a greater surface area. The number of trabeculae also increases, increasing the density of subchondral cancellous bone (sclerosis) to better resist applied forces. No destruction or degeneration of articular soft tissues occurs. TMJ remodeling occurs throughout adult life and is considered abnormal only if it is accompanied by clinical signs and symptoms of pain or dysfunction or if the degree of remodeling seen radiographically is judged to be severe. Remodeling may be unilateral and does not invariably serve as a precursor to degenerative joint disease.

Clinical Features

Remodeling may be asymptomatic, or patients may have signs and symptoms of temporomandibular dysfunction that may be related to the soft tissue components, associated muscles, or ligaments. Accompanying internal derangement of the disk may be a factor.

Radiographic Features

Radiographic changes may affect the condyle, temporal component, or both; they first occur on the anterosuperior surface of the condyle and the posterior slope of the articular eminence. The lateral aspect of the joint is affected in early stages, and the central and medial aspects become involved as remodeling progresses. The radiographic appearance may include one or a combination of the following: flattening, cortical thickening of articulating surfaces, and subchondral sclerosis (Fig. 26-21).

Differential Diagnosis

Severe joint flattening and subchondral sclerosis may be difficult to differentiate from early degenerative joint disease. It is known that the microscopic changes of degeneration occur before they can be detected radiographically. The radiographic appearance of bone erosions, osteophytes, and loss of joint space are signs signifying degenerative joint disease.

Treatment

When no clinical signs or symptoms are present, treatment is not indicated. Otherwise, treatment directed to relieve stress on the joint, such as splint therapy, may be considered. This should be preceded by an attempt to discover the cause of the joint stress.

Synonym

Osteoarthritis

Definition

Degenerative joint disease (DJD) is a noninflammatory disorder of joints characterized by joint deterioration and proliferation. Joint deterioration is characterized by loss of articular cartilage and bone erosion. The proliferative component is characterized by new bone formation at the articular surface and in the subchondral region. Usually a variable combination of deterioration and proliferation occurs, but occasionally one aspect predominates; deterioration is more common in acute disease, and proliferation predominates in chronic disease. DJD is thought to occur when the ability of the joint to adapt to excessive forces (remodel) is exceeded. The etiology of DJD is unknown, although a number of factors may be important, including acute trauma, hypermobility, and loading of the joint such as occurs in parafunction. Internal disk derangements may be contributing etiologic factors, but this theory is controversial.

Clinical Features

DJD can occur at any age, although the incidence increases with age. DJD has a female preponderance. The disease may be asymptomatic, or patients may complain of signs and symptoms of TMJ dysfunction, including pain on palpation and movement, joint noises (crepitus), limited range of motion, and muscle spasm. The onset of symptoms may be sudden or gradual, and symptoms may disappear spontaneously, only to return in recurring cycles. Some studies report that the disease eventually “burns out” and symptoms disappear or markedly decrease in severity in long-standing cases.

Radiographic Features

Osseous changes in DJD are more accurately depicted in CT images, but gross osseous changes may be evident in MRI studies, particularly in T1-weighted images. When the patient is in maximal intercuspation, the joint space may be narrow or absent, which often correlates with an internal derangement and frequently with a perforation of the disk or posterior attachment, resulting in bone-to-bone contact of the joint components. Signs of previous remodeling, such as flattening and subchondral sclerosis, may be evident, although degenerative changes may obscure these findings. Loss of cortex or erosions of the articulating surfaces of the condyle or temporal component (or both) are characteristic of this disease (Fig. 26-22). In some cases small, round, radiolucent areas with irregular margins surrounded by a varying area of increased density are visible deep to the articulating surfaces. These lesions are called “Ely” or subchondral bone cysts but are not true cysts; they are areas of degeneration that contain fibrous tissue, granulation tissue, and osteoid (Fig. 26-22).

Later in the course of the disease, bony proliferation occurs at the periphery of the articulating surface, increasing the articulating surface area. This new bone is called an osteophyte, which typically appears on the anterosuperior surface of the condyle, the lateral aspect of the temporal component, or both (Fig. 26-23). Osteophytes also may form on the lateral, medial, and posterosuperior aspects of the condyle. In severe cases, osteophyte formation originating in the glenoid fossa extends from the articular eminence to almost encase the condylar head. Osteophytes may break off and lie free within the joint space (these fragments are known as “joint mice”), and these must be differentiated from other conditions that cause joint space radiopacities (Figs. 26-23 and 26-24). It has been reported that joints with long-term nonreducing disk displacement have a higher incidence of progressive radiographic changes of DJD than in joints with no disk displacement or reducing disks.

In severe DJD, the glenoid fossa may appear grossly enlarged because of erosion of the posterior slope of the articular eminence, and the condyle may be markedly diminished in size and altered in shape because of destruction and erosion of the condylar head. This in turn may allow the condylar head to move forward and superiorly into an abnormal anterior position that may result in an anterior open bite.

Differential Diagnosis

DJD can have a spectrum of appearances ranging from substantial subchondral sclerosis and osteophyte formation (proliferative component) to extensive erosions (degenerative component). A more erosive appearance may simulate inflammatory arthritides such as rheumatoid arthritis, whereas a more proliferative appearance with extensive osteophyte formation may simulate a benign tumor such as osteoma or osteochondroma.

Treatment

Treatment is directed toward relieving joint stress (e.g., splint therapy), relieving secondary inflammation with anti-inflammatory drugs, and increasing joint mobility and function (e.g., physiotherapy).

Definition

Rheumatoid arthritis (RA) is a heterogeneous group of systemic disorders that manifests mainly as synovial membrane inflammation in several joints. The TMJ becomes involved in approximately half of affected patients. The characteristic radiographic findings are a result of villous synovitis, which leads to formation of synovial granulomatous tissue (pannus) that grows into fibrocartilage and bone, releasing enzymes that destroy articular surfaces and underlying bone.

Clinical Features

RA is more common in females and can occur at any age but increases in incidence with increasing age. A juvenile variant is discussed separately. Usually the small joints of the hands, wrists, knees, and feet are affected in a bilateral, symmetric fashion, whereas TMJ involvement varies. Patients with TMJ involvement complain of swelling, pain, tenderness, stiffness on opening, limited range of motion, and crepitus. The chin appears receded, and an anterior open bite is a common finding because of the bilateral destruction and anterosuperior positioning of the condyles. TMJ involvement usually is bilateral and symmetric.

Radiographic Features

The initial changes may be generalized osteopenia (decreased density) of the condyle and temporal component. The pannus may destroy the disk, resulting in diminished width of the joint space. Bone erosions by the pannus most often involve the articular eminence and the anterior aspect of the condylar head, which permits anterosuperior positioning of the condyle when the teeth are in maximal intercuspation and results in an anterior open bite (Fig. 26-25). Erosion of the anterior and posterior condylar surfaces at the attachment of the synovial lining may result in a “sharpened pencil” appearance of the condyle. Erosive changes may be so severe that the entire condylar head is destroyed, with only the neck remaining as the articulating surface. Similarly, the articular eminence may be destroyed to the extent that a concavity replaces the normally convex eminence. Joint destruction eventually leads to secondary DJD. Subchondral sclerosis and flattening of articulating surfaces may occur, as well as subchondral “cyst” and osteophyte formation. Fibrous ankylosis or, in rare cases, osseous ankylosis, may occur (Fig. 26-26); reduced mobility is related to the duration and severity of the disease.

Differential Diagnosis

The differential diagnosis includes severe DJD and psoriatic arthritis. Osteopenia and severe erosions, particularly of the articular eminence, are more characteristic of RA. Psoriatic arthritis may be ruled out by the patient’s history.

Treatment

Treatment is directed toward pain relief (analgesics), reduction or suppression of inflammation (nonsteroidal anti-inflammatory drugs, gold salts, corticosteroids), and preservation of muscle and joint function (physiotherapy). Joint replacement surgery may be necessary in patients with severe joint destruction.

Synonyms

Juvenile rheumatoid arthritis, juvenile chronic arthritis, and Still’s disease

Definition

Juvenile arthritis (JA), formerly called juvenile rheumatoid arthritis and juvenile chronic arthritis, is a chronic inflammatory disease that appears before the age of 16 years (the mean age is 5 years). It is characterized by chronic, intermittent synovial inflammation that results in synovial hypertrophy, joint effusion, and swollen, painful joints. As the disease progresses, cartilage and bone are destroyed. Rheumatoid factor may be absent, hence the preferred terminology of JA rather than juvenile rheumatoid arthritis. JA differs from adult RA in that it has an earlier onset, and systemic involvement usually is more severe. TMJ involvement occurs in approximately 40% of patients and may be unilateral or bilateral.

Clinical Features

The patient usually has pain and tenderness in the affected joint or joints, although the disease can be asymptomatic. Unilateral onset is common, but contralateral involvement may occur as the disease progresses. Severe TMJ involvement results in inhibition of mandibular growth. Affected patients may have micrognathia and posteroinferior chin rotation, resulting in a facial appearance known as “bird face,” which may also be accompanied by an anterior open bite. The degree of micrognathia is proportional to the severity of joint involvement and the early onset of disease. Additionally, when only one TMJ is involved or if one side is more severely affected, the patient may have a mandibular asymmetry with the chin deviated to the affected side.

Radiographic Features

Osteopenia (decreased density) of the affected TMJ components may be the only initial radiographic finding. Radiographic findings are similar to those for the adult form except for the addition of impaired mandibular growth. Erosions may extend to the mandibular fossa, and the articular eminence may be destroyed. Similarly, erosion of the anterior or superior aspect of the condyle may occur, and in more severe cases only a pencil-shaped small condyle remains; the condyle may be destroyed. Because the inflammation is intermittent, during quiescent periods the cortex of the joint surfaces may reappear, and the surfaces will appear flattened. As a result of bone destruction, the condylar head typically is positioned anterosuperiorly in the mandibular fossa (Fig. 26-27). Hypomobility at maximal opening is common, and fibrous ankylosis may occur in some cases. Secondary degenerative changes manifesting as sclerosis and osteophyte formation may be superimposed on the rheumatoid changes, and ankylosis may occur. An abnormal disk shape is often observed in patients with long-term TMJ involvement. Manifestations of inhibited mandibular growth, such as deepening of the antegonial notch, diminished height of the ramus, and dorsal bending of the ramus and condylar neck, also may occur unilaterally or bilaterally, resulting in an obtuse angle between the mandibular body and the ascending ramus.

Synonym

Infectious arthritis

Definition

Septic arthritis is infection and inflammation of a joint that can result in joint destruction. It is rare in comparison to the incidence of DJD and RA in the TMJ. Septic arthritis may be caused by direct spread of organisms from an adjacent cellulitis or from parotid, otic, or mastoid infections. It also may occur by direct extension of osteomyelitis of the mandibular body and ramus or spread from a middle ear infection, although hematogenous spread from a distant nidus has also been reported. Other causes include systemic and autoimmune diseases (e.g., RA, diabetes, immunosuppression, hypogammaglobulinemia), prolonged use of systemic steroids, and sexually transmitted diseases. Septic arthritis has also been reported in children after blunt trauma, as a result of hyperemia and increased exposure to microorganisms, damage to local structure allowing bacterial access, or hematoma formation providing a favorable growth medium.

Clinical Features

Individuals can be affected at any age, and the condition shows no sex predilection. It usually occurs unilaterally. The patient may have redness and swelling over the joint; trismus; severe pain on opening; inability to occlude the teeth; large, tender cervical lymph nodes; fever; and malaise. The mandible may be deviated to the unaffected side as a result of joint effusion.

Radiographic Features

No radiographic signs may be present in early stages of the disease, although the space between the condyle and the roof of the mandibular fossa may be widened because of inflammatory exudate in the joint spaces. Osteopenic (radiolucent) changes of the joint components and mandibular ramus may be evident. More obvious bony changes are seen approximately 7 to 10 days after the onset of clinical symptoms. As a result of the osteolytic effects of inflammation, the condylar articular cortex may become slightly radiolucent, erosions of the surface of the condyle and articular eminence may be seen, sequestra may become apparent, and there may be periosteal new bone formation (Fig. 26-28). As the disease progresses, the condyle and articular eminence, including the disk, may be destroyed. Osseous ankylosis may occur after the infection subsides. If the disease occurs during the period of mandibular growth, radiographic manifestations of inhibited mandibular growth may be evident.

Differential Diagnosis

The diagnosis of septic arthritis is ideally made by identification of organisms in joint aspirate, although cultures occasionally remain negative. The radiographic changes caused by septic arthritis may mimic those of severe DJD or RA, although septic arthritis usually occurs unilaterally, and the patient often has clinical signs and symptoms of infection. Inflammatory changes that may accompany septic arthritis may be seen in CT images, such as involvement of mastoid air cells, osteomyelitis of the mandible, and inflammation of surrounding soft tissue. MRI, with T2-weighted images, may show muscle enlargement, joint effusion, or abscess. Scintigraphy by use of a technetium bone scan will show increased bone metabolism within the osseous components, especially the condyle, and gallium confirms the presence of infection.

Treatment

Treatment includes antimicrobial therapy, drainage of effusion, and joint rest. Physiotherapy to re-establish joint mobility is initiated after the acute phase of infection has passed.

Synonyms

Synovial chondrometaplasia and osteochondromatosis

Definition

Synovial chondromatosis is an uncommon disorder characterized by metaplastic formation of multiple cartilaginous and osteocartilaginous nodules within connective tissue of the synovial membrane of joints. Some of these nodules may detach and form loose bodies in the joint space, where they persist and may increase in size, being nourished by synovial fluid. This condition is more common in the axial skeleton than in the TMJ. When the cartilaginous nodules ossify, the term synovial osteochondromatosis may be used.

Clinical Features

Patients may be asymptomatic or may complain of preauricular swelling, pain, and decreased range of motion. Some patients have crepitus or other joint noises. The condition usually occurs unilaterally.

Radiographic Features

The osseous components may appear normal or may exhibit osseous changes similar to those in DJD. The joint space may be widened, and if ossification of the cartilaginous nodules has occurred, a radiopaque mass or several radiopaque loose bodies may be seen surrounding the condylar head (Fig. 26-29). CT imaging can identify the location of the calcifications. Sclerosis of the glenoid fossa and condyle may be seen, which is considered to be a chronic bone reaction to an active lesion. Occasionally, erosion through the glenoid fossa into the middle cranial fossa may occur, which is best detected with CT. MRI may be useful in defining the tissue planes between the synovial chondromatosis mass and surrounding soft tissue.

Differential Diagnosis

The appearance of synovial osteochondromatosis cannot always be differentiated from chondrocalcinosis; however, often the soft tissue calcifications in osteochondromatosis are larger and may have a peripheral cortex that identifies their bony nature. Conditions that appear similar include DJD with joint mice or chondrosarcoma or osteosarcoma. Either sarcoma may be accompanied by severe bone destruction, which may help in differentiating the condition from synovial chondromatosis.

Treatment

Treatment consists of removal of the loose bodies and resection of abnormal synovial tissue in the joint by arthroscopic or open joint surgery.

Synonyms

Pseudogout and calcium pyrophosphate dihydrate deposition disease

Definition

Chondrocalcinosis is characterized by acute or chronic synovitis and precipitation of calcium pyrophosphate dihydrate crystals in the joint space. It differs from gout, in which urate crystals are precipitated, hence the term pseudogout.

Clinical Features

The joints more commonly affected are the knee, wrist, hip, shoulder, and elbow; TMJ involvement is uncommon. The condition occurs unilaterally and is more common in males. Patients may be asymptomatic or may complain of pain and joint swelling.

Radiographic Features

The radiographic appearance of chondrocalcinosis may simulate synovial chondromatosis, described previously. Often the radiopacities within the joint space are finer and have a more even distribution than in osteochondromatosis (Fig. 26-30). Bone erosions and a severe increase in condylar bone density also have been described. Erosions of the glenoid fossa may be present, which require CT for detection. Soft tissue swelling and edema of the surrounding muscles may be seen with MRI.

Differential Diagnosis

The differential diagnosis is the same as for synovial chondromatosis.

Treatment

Treatment consists of surgical removal of the crystalline deposits. Steroids, aspirin, and nonsteroidal anti-inflammatory agents may provide relief. Colchicine may be used to alleviate acute symptoms and for prophylaxis.

Definition

Effusion is an influx of fluid into the joint, usually as a result of trauma (hemorrhage) or inflammation (exudate). Inflammation may result from an internal derangement, traumatic injuries, arthritis, or rheumatic diseases.

Clinical Features

The patient may have swelling over the affected joint; pain in the TMJ, preauricular region, or ear; and limited range of motion. Patients may also complain of the sensation of fluid in the ear, tinnitus, hearing difficulties, and difficulty occluding the posterior teeth.

Radiographic Features

Joint effusion is more commonly seen in conjunction with internal derangements, although it has been described in normal joints. The joint space is widened, and T2-weighted MRI studies may show a bright signal (white), indicating fluid adjacent to the disk or posterior to the condyle (see Fig. 26-19).

Differential Diagnosis

Effusion must be differentiated from septic arthritis; in the latter case the accompanying signs and symptoms of infection are present.

Treatment

Treatment may include anti-inflammatory drugs, although surgical drainage of the effusion occasionally is necessary.

Definition

Dislocation is abnormal positioning of the condyle out of the mandibular fossa but within the joint capsule. It usually occurs bilaterally and most commonly in an anterior direction. Dislocation may be caused by a failure of muscular coordination, subluxation, or external trauma and may be associated with a condylar fracture. Dislocation may occur into the middle cranial fossa as a result of trauma, but this is rare.

Clinical Features

In anterior dislocation, patients are unable to close the mandible to maximal intercuspation; some patients cannot reduce the dislocation, whereas others may be able to reduce the mandible by manipulation. In the former case associated pain and muscle spasm often are present.

Radiographic Features

In bilateral cases both condyles are located anterior and superior to the summits of the articular eminentia. Clinical information is important because the normal range of motion may extend anterior to the summit of the articular eminence.

Differential Diagnosis

The diagnosis is confirmed by the radiographic findings, although some fracture dislocations may be difficult to visualize, particularly if the dislocation is very slight. For this reason, CT or tomography is essential for diagnosis because routine plain film views may not show the dislocation because of anatomic superimpositions.

Treatment

Treatment consists of manual manipulation of the mandible to reduce the dislocation. Surgery occasionally is necessary to reduce the condyle in the case of a fracture dislocation, although treatment may not be indicated for this type of dislocation if mandibular function is adequate.

Definition

Fractures of the TMJ usually occur at the condylar neck and often are accompanied by dislocation of the condylar head. Fractures may be classified according to the anatomic location of the fracture: condylar head, condylar neck, and subchondral region. Occasionally more than one anatomic location is involved. On rare occasions the fracture may involve the temporal component.

Clinical Features

Unilateral fractures, which are more common than bilateral fractures, may be accompanied by a parasymphyseal or mandibular body fracture on the contralateral side. The patient may have swelling over the TMJ, pain, limited range of motion, and an anterior open bite. Some TMJ fractures are relatively asymptomatic and may not be discovered at the time of trauma; instead, these come to light as incidental findings at a later time when radiographs are taken for other reasons. Condylar fractures should be ruled out if the patient has a history of a blow to the mandible, especially to the anterior aspect.

If a condylar fracture occurs during the period of mandibular growth, growth may be inhibited because of damage to the condylar growth center. The degree of subsequent hypoplasia is related to the stage of mandibular development at the time of injury (younger patients have more profound hypoplasia) and the severity of the injury. Patients younger than 10 years old have a higher remodeling potential and may have less deformity compared with older patients, although injuries in patients younger than 3 years old tend to produce severe asymmetries. Injury to the joint may result in hemorrhage or effusion into the joint spaces that eventually may form bone during the healing process, which in turn may result in severe hypoplasia and limited joint function.

Radiographic Features

In relatively recent condylar neck fractures, a radiolucent line limited to the outline of the neck is visible. This line may vary in width, depending on whether the bone fragments are still aligned (narrow line) or displacement/dislocation has occurred (wider line). If the bone fragments overlap, an area of apparent increase in radiopacity may be seen instead of a radiolucent line (Fig. 26-31). Also, the outer cortical boundary may have an irregular outline or a step defect. Approximately 60% of condylar fractures show evidence of fragment angulation and a variable degree of displacement (dislocation) of the fracture ends. Fractures of the condylar head are less common and may be of the vertical (responsible for the traumatic type of bifid condyle) or compressive type (Fig. 26-32). CT is the preferred imaging modality to evaluate condylar fractures because there is no superimposition of adjacent structures and TMJ reformats provide images in several different planes. Two- and three-dimensional reformatted images are useful to accurately locate a fractured fragment. Alternatively, if CT is not available, multiple right-angle radiographic projections from the lateral, frontal, and basilar aspects may be used to detect a fracture.

The amount of remodeling seen in the TMJ after a condylar fracture with medial displacement varies considerably. In some cases the condyle remodels to a form that is essentially normal, whereas in other cases the condyle and mandibular fossa become flattened, with loss of vertical height on the affected side. The condyle eventually may show degenerative changes, including flattening, erosion, osteophyte formation, and ankylosis. These changes are more severe if the condyle is displaced. Condylar fractures can also be associated with damage of the intracapsular soft tissues, including the disk, joint capsule and retrodiskal tissues, and with hemarthrosis and joint effusion.

Differential Diagnosis

Occasionally old fractures that have remodeled may be difficult to differentiate from developmental abnormalities of the condyle. The most common difficulty is in determining whether a fracture is indeed present. Panoramic views taken as an initial examination must be supplemented with a Towne’s view, especially if there is suspected medial displacement of the condylar head.

Treatment

Treatment may not be indicated if mandibular mobility is adequate; otherwise, the fracture is reduced surgically.

The use of forceps during delivery of neonates may result in fracture and displacement of the rudimentary condyle, which later manifests as severe mandibular hypoplasia and lack of development of the glenoid fossa and articular eminence. Such cases have a characteristic radiographic appearance in the panoramic image, having the appearance of a partly opened pair of scissors in place of a normal condyle (Fig. 26-33). This presentation results from the overlapping images of the medially displaced carrot-shaped condyle and remnants of the condylar neck.

Differential Diagnosis

This condition often is not diagnosed until later in life, at which time a diagnosis of fracture may be made without a history that the fracture occurred at the time of birth. The condition must be differentiated from a developmental hypoplasia of the mandible, which is unrelated to birth injury.

Treatment

The fracture usually is not treated, but the mandibular asymmetry may be corrected with a combination of orthodontics and orthognathic surgery.

Definition

Ankylosis is a condition in which condylar movement is limited by a mechanical problem in the joint (“true” ankylosis) or by a mechanical cause not related to joint components (“false” ankylosis). True ankylosis may be bony or fibrous. In bony ankylosis the condyle or ramus is attached to the temporal or zygomatic bone by an osseous bridge. In fibrous ankylosis a soft tissue (fibrous) union of joint components occurs; the bone components appear normal. False ankylosis may result from conditions that inhibit condylar movement, such as muscle spasm, myositis ossificans, or coronoid process hyperplasia.

Clinical Features

Most unilateral cases are caused by mandibular trauma or infection. The most common cause of bilateral TMJ ankylosis is rheumatoid arthritis, although in rare cases bilateral fractures may be the cause. Most if not all cases of TMJ ankylosis in infancy occur as a result of birth injury. Patients have a history of progressively restricted jaw opening, or they may have a long-standing history of limited opening. Some degree of mandibular opening usually is possible through flexing of the mandible, although opening may be restricted to only a few millimeters, particularly in the case of bony ankylosis.

Radiographic Features

In fibrous ankylosis the articulating surfaces are usually irregular because of erosions. The joint space is usually very narrow and the two irregular surfaces may appear to fit one another like a jigsaw puzzle (see Fig. 26-26). Little or no condylar movement is seen. Radiographic signs of remodeling occasionally are visible as the joint components adapt to repeated attempts at mandibular opening. In bony ankylosis the joint space may be partly or completely obliterated by the osseous bridge, which can vary from a slender segment of bone, which may be difficult to locate, to a large bony mass. This extensive new bone may fuse the condyle to the cranial base (Fig. 26-34). Secondary degenerative changes of the joint components are common. Often morphologic changes occur, such as compensatory progressive elongation of the coronoid processes and deepening of the antegonial notch in the mandibular ramus on the affected side as a result of muscle function during attempted mandibular opening. If ankylosis occurs before mandibular growth is complete, growth of the affected side of the mandible is inhibited. Coronal CT images are the best diagnostic imaging method to evaluate ankylosis.

Differential Diagnosis

The major differential diagnosis is a condylar tumor. However, a history of trauma, infection, or other joint diseases should help rule out neoplastic disease. Detection of fibrous ankylosis is difficult because fibrous tissue is not visible in the radiographic image and therefore may be difficult to differentiate from false ankylosis.

Treatment

Joint mobility is improved by surgical removal of the osseous bridge or creation of a pseudarthrosis.

Clinical Features

Condylar tumors grow slowly and may attain considerable size before becoming clinically noticeable. Patients may complain of TMJ swelling, which may be accompanied by pain and decreased range of motion; the symptoms often mimic TMJ dysfunction. The clinical examination may reveal facial asymmetry, malocclusion, and deviation of the mandible to the unaffected side; these may be accompanied by symptoms of TMJ dysfunction. Tumors of the coronoid process typically are painless, but patients may complain of progressive limitation of motion.

Radiographic Features

Condylar tumors cause condylar enlargement that often is irregular in outline. The trabecular pattern may be altered, resulting in regions of destruction seen as radiolucencies or new abnormal bone formation, which may increase the radiopacity of the condyle with abnormal trabeculae. An osteoma or osteochondroma appears as an abnormal, pedunculated mass attached to the condyle (Fig. 26-35). Osteochondromas often extend from the anterior or superior surface of the condyle. Tumors of the coronoid process may affect TMJ function, which emphasizes the need to image and evaluate the coronoid process when evaluating joint abnormalities. The most common benign tumor is the osteochondroma. This tumor may interfere with joint function and erode adjacent osseous structures.

Differential Diagnosis

Condylar neoplasms may simulate unilateral condylar hyperplasia because of condylar enlargement, although osteomas and osteochondromas give an irregular appearance, such as bulbous or globular expansion of the condyle or, more commonly, a pedunculated growth. Also, the characteristic condylar shape and proportions are better preserved in condylar hyperplasia. Coronoid tumors must be differentiated from coronoid hyperplasia, which differs from a condylar tumor in that the coronoid process remains regular in shape.

Treatment

Treatment consists of surgical excision of the tumor and occasionally excision of the condylar head or coronoid process.

Malignant tumors of the jaws may be primary or, more commonly, metastatic. Primary intrinsic malignant tumors of the condyle are extremely rare and include chondrosarcoma, osteogenic sarcoma, synovial sarcoma, and fibrosarcoma of the joint capsule. Extrinsic malignant tumors may represent direct extension of adjacent parotid salivary gland malignancies, rhabdomyosarcoma (particularly in children), or other regional carcinomas from the skin, ear, and nasopharynx. The most common metastatic lesions include neoplasms originating in the breast, kidney, lung, colon, prostate, and thyroid gland.

Clinical Features

Malignant tumors (primary or metastatic) may be asymptomatic or patients may have symptoms of TMJ dysfunction such as pain, limited mandibular opening, mandibular deviation, and swelling. Unfortunately, a patient occasionally is treated for TMJ dysfunction without recognition that the underlying condition is a malignancy.

Radiographic Features

Malignant primary and metastatic TMJ tumors appear as a variable degree of bone destruction with ill-defined, irregular margins. Most lack tumor bone formation, with the exception of osteogenic sarcoma. Chondrosarcoma may appear as an indistinct, essentially radiolucent destructive lesion of the condyle with surrounding discrete soft tissue calcifications that may simulate the appearance of the articular loose bodies seen in chondrocalcinosis or pseudogout (Fig. 26-36). In the case of metastatic tumors, the radiographic appearance usually is nonspecific condylar destruction (with a few exceptions, such as metastatic prostate carcinoma) and does not indicate the site of origin (Fig. 26-37). CT is the imaging modality of choice to view bone involvement and MRI is useful for displaying the extent of involvement into the surrounding soft tissues.

Differential Diagnosis

Joint destruction caused by a malignant tumor must be differentiated from the osseous destruction seen in severe DJD. Malignant tumors cause profound central bone destruction, whereas DJD causes more peripheral bone destruction. Proliferative changes such as osteophyte formation may be seen in DJD, but unlike with a malignant tumor, no soft tissue mass or swelling is evident. Chondrosarcoma may simulate joint space calcifications (discussed earlier), but in the case of malignancy, severe bone destruction also occurs.

Treatment

In the case of primary malignant tumors, treatment consists of wide surgical removal of the tumor. Tumor extension to vital anatomic structures may compromise survival. Metastatic tumors of the TMJ rarely are treated surgically; treatment mainly is palliative and may include radiotherapy and chemotherapy.