eMedicine Specialties > Radiology > Head/Neck
Temporomandibular Joint, Meniscus Abnormalities
Updated: Apr 29, 2008
Introduction
Background
Symptomatic temporomandibular joint (TMJ) dysfunction affects 28% of the adult population, with a smaller, although significant, percentage experiencing severe impairment.1,2 The clinical problem is complex, because TMJ dysfunction is multifactorial. Although most occurrences are related to internal derangement, many joints are painful secondary to nondiskogenic causes, such as referred pain from spondylosis of the upper cervical spine and other inflammatory and neoplastic bone lesions in the vicinity of the TMJ. A variety of pathologies may affect the TMJ, of which internal derangement is the most common.
The etiology of internal derangement is obscure, although in 25% of patients, a history of trauma is elicited; in these cases, 30% of the causes are iatrogenic and result, for example, from procedures that necessitate jaw extension. These include tonsillectomy, endoscopy, and molar tooth extraction.
Typically, the patient with TMJ dysfunction is a young woman aged 20-40 years who has experienced symptoms for 3-5 years. Not uncommonly, misdiagnosis continues for several years, particularly during childhood and adolescence, because of a variety of poorly understood presenting symptoms. As a result, severe degenerative changes in the TMJ are observed even in children.
The objective of conservative and surgical treatment is to shorten the period of the patient's symptoms and to reduce the incidence of long-term joint disfigurement, such as osteoarthrosis, ankylosis, and avascular necrosis. A variety of splints are used to change the position of the meniscus and/or occlusion, but although splints may stabilize the joint, they cannot reverse joint pathology.3 The most commonly performed surgical procedures include diskal plication with repositioning of the disk, and simple diskectomy, with or without the employment of a disk implant.4
Various alloplastic and autogenous materials can be used to fashion a disk implant, such as Teflon, silicon, silastic, and fascial, dermal, and rib grafts. The object of the disk implant is to reduce the probability of osteoarthrosis, adhesions, and recurrent pain and dysfunction. In more advanced cases, condylectomy and reduction osteotomy of the articular eminence may be necessary. The complications of joint stabilization may cause continued TMJ pain; these complications include avascular necrosis, osteochondritis dissecans, and osteoporosis, which may lead to progressive bone remodeling.
Advances in imaging have contributed greatly to the understanding and treatment of TMJ dysfunction and related pathologies. Currently, magnetic resonance imaging (MRI) is regarded as the modality of choice in the evaluation of TMJ dysfunction, although other modalities still have specific roles to play.5,6,7,8
Tomogram through the left temporomandibular joint showing a hypoplastic mandibular condyle with minor remodeling. Both sides were examined with the mouth open and closed. Note the limitation of movement on both sides (see Image 5 in Multimedia).
Coronal 5-mm CT cut through the anterior cranial fossa and sinuses showing a right maxillary tumor invading the lateral sinus wall and destroying the right ramus and condyle of the mandible. Same patient as in Images 9-11 in Multimedia.
Sagittal T1-weighted MRI image through the left temporomandibular joint showing an anterior disk displacement (open mouth) without recapture of the meniscus (closed mouth). A small arrow has marked the meniscus (see Image 15 in Multimedia).
Frontal and lateral (right and left) radionuclide images of the skull showing intense activity in the left temporomandibular joint in a 41-year-old woman with an MRI-confirmed temporomandibular joint meniscus dysfunction.
Pathophysiology
The TMJ is a synovial joint. The same diseases and disorders that affect other parts of the musculoskeletal system also affect the TMJ. Thus, internal derangement, degenerative joint disease (arthrosis), inflammatory arthritis, infection, and synovitis all are seen in the TMJ.1,2,6,9 The basic terminology for describing patients with signs and symptoms of TMJ disorders has not been standardized, and a multitude of terms have been used.
Because of the lack of strict criteria for differential diagnosis, clinicians and researchers have used broader diagnostic categories, such as mandibular dysfunction, TMJ syndrome, craniomandibular disorders, and temporomandibular disorders. These are all loosely defined umbrella terms and include several entities that have a different etiology but may present with similar signs and symptoms. Disorders of the TMJ represent 1 subgroup of any of these umbrella terms.
In general, causes of internal derangements leading to TMJ disorder can be classified under the broad headings of acute macrotrauma, chronic microtrauma, or developmental and acquired defects.
- Acute macrotrauma is macrotrauma that involves an external source of injury to the TMJ, such as a blow to the mandible, mandibular whiplash, and mandibular hyperextension. Mandibular hyperextension can occur in oral surgical procedures and intubations performed for general anesthesia.
- Chronic microtrauma is microtrauma that involves a source of low-grade trauma to the TMJ over a long period of time. Included in this category are forces that overload the joint complex or disturb the normal relationship of the condyle, disk, and eminence. Bruxism, and clenching in particular, can have a destructive effect on the TMJ through excessive overloading. Articular remodeling, which is the normal adaptive response of healthy tissue to mechanical forces acting on the joint, can be replaced by degenerative changes. In the TMJ, the articular disk is more vulnerable to degeneration and deformation than are the articular surfaces of the condyle and eminence.
- Developmental and acquired defects include numerous developmental, growth, and acquired defects that can alter the structural integrity of the TMJ components. Developmental anomalies include hypoplastic and hyperplastic condyles, along with various skeletal and facial asymmetries. Various endocrine and nutritional disturbances, as well as tumors, can involve the TMJ, leading to a disruption in function. Convincing evidence exists that disk displacement often, but not always, is responsible for the mechanical symptoms seen in patients with TMJ pain and dysfunction, but disk displacement also may be seen in asymptomatic persons. Disk displacement can occur in any of the various directions.
- Anterior disk displacement is defined as an alteration of the position of the disk from its expected normal location on top of the condyle, that is, a deviation from the relationship between the posterior band of the disk and the 12 o'clock location on top of the condyle.
- In sideways and rotational displacements, the disk may be displaced in the lateral, medial, and, very rarely, posterior directions. Most frequently, the medial and lateral displacements are associated with anterior displacement and are termed rotational displacement.
- Partial and complete displacements include displacement of the disk in any direction, which also may be complete or partial. Partial disk displacement implies that one part of the disk remains interposed between the condyle and the glenoid fossa, while another part of the disk has been displaced out of its normal position. Complete disk displacement implies that the entire disk has been displaced out of its normal position. Commonly, simple lateral and simple medial displacements are partial types of displacement.
- Disk displacement with reduction specifies that the displaced disk return to a normal superior position relative to the condyle during jaw opening. This condition frequently is associated with clicking. During closing of the jaw, the disk again is displaced anteriorly. This also is associated with a subtler clicking or irregularity of movement. This type of double clicking has been termed reciprocal clicking, stressing the dependence of the closing click on the opening click.
- Disk displacement with incomplete reduction specifies that the anteriorly displaced disk be only partially recaptured on opening. Part of the disk remains in the displaced position, while another part is in a normal position on opening.
- In orthopedic terminology, internal derangement is defined as soft tissue between joint surfaces interfering with the smooth action of a joint. If the disk is displaced from its normal position on top of the condyle and interferes with the smooth action of the joint, internal derangement ensues. Conversely, if the disk is displaced but causes no interference with the function of the joint (ie, no clicking, irregular movement, or limitation of opening), no internal derangement is present, according to the general definition.
Frequency
United States
Studies indicate that 10-45% of the population experiences TMJ symptoms at some point during their lifetime.
International
Exact incidence of TMJ dysfunction is not known, but the figure quoted is approximately 28% of the adult population.
Mortality/Morbidity
TMJ dysfunction secondary to internal derangement is a progressive disorder eventually resulting in ankylosis and osteoarthrosis of varying severity. The end result of the time-dependent deforming changes is automeniscectomy, ideally with resolution of symptoms. TMJ internal derangement eventually reaches clinical quiescence after a clinical course of waxing and waning of disabling symptoms, usually over a period of 6-10 years. The objective of conservative and surgical treatment is to shorten the period of the patient's symptoms and to reduce the incidence of long-term joint disfigurement, such as osteoarthrosis, ankylosis, and avascular necrosis.10,11
Race
No racial predilection exists.
Sex
A striking sex predilection is noted, with TMJ dysfunction occurring far more frequently in females than it does in males; the quoted male-to-female ratio is 1:10.
Age
Most patients are aged 20-40 years, but children can be affected. The disorder is rare in older age groups.
Anatomy
Normally, the TMJ is a freely movable articulation between the condyle of the mandible and the squamous portion of the temporal bone at the base of the skull. The bilateral articulation of the mandible to the cranium implies that the left and right TMJs must act as a single unit. The osseous and soft-tissue components of the joints are described in this section.
Osseous components
Osseous components of the TMJ consist inferiorly of the mandibular condyle and superiorly of the glenoid fossa and articular eminence. The mandibular condyle crowns the mandibular neck. It is elliptic in shape and resembles a large olive that is oriented horizontally. The lateral pole of the condyle is located approximately 1-1.5 cm beneath the skin. Each mandibular condyle measures an average of 20 mm mediolaterally and 10 mm anteroposteriorly. The horizontal long angles of the mandibular condyles usually converge in a posterior direction. The angle between the horizontal condylar long axis and the frontal plane has been shown to have a mean value of 15°.
The temporal component of the TMJ consists of the concave glenoid (mandibular) fossa and the convex articular tubercle, both of which are formed by the squamous part of the temporal bone. The temporal part of the joint measures approximately 23 mm in mediolateral width and in anteroposterior length; it is measured using capsular attachments as the margins. Medially, the fossa narrows considerably and is closed by an osseous plate that prevents the condyle from being displaced medially.
Soft-tissue components
The interposed disk divides the joint into upper and lower joint compartments, which normally do not communicate. The disk is a flexible but firm plate of dense, collagenous connective tissue that merges around its periphery with the surrounding capsule. Its central part is considerably thinner than its periphery, and its posterior band is considerably thicker. The inferior aspect of the disk is concave and fits on top of the rounded condyle.
The peripheral attachment to the capsule binds the disk firmly to the lateral and medial poles of the condyle. Anteriorly, no direct connection exists between the disk and the mandibular condyle. Thus, the disk can rotate relatively freely over the condyle in an anteroposterior direction, but it is capable of relatively little movement in the mediolateral direction unless the attachments to the capsule and condyle have been torn or elongated.
Anterior movement of the disk is limited by the length of the undersurface of the posterior disk attachment. This extends from the posterior band of the disk down to the back of the condyle and prevents the disk from moving anteriorly over the condyle. The normal position of the disk traditionally has been described as a 12 o'clock relationship between the superior aspect of the condyle and the posterior band of the disk. However, not all normal joints show an ideal superior disk position. When the posterior band is not in the perfect 12 o'clock position, the relationship between the anterior prominence of the condyle and the central thin zone of the disk should be interrogated.
Separation of the anterior prominence of the condyle and central thin zone of the disk is evidence of disk displacement. The TMJ capsule originates from the periphery of the articulating surface of the temporal bone. It extends inferiorly in the shape of a funnel, encloses the disk and condyle, and attaches to the lower part of the condyle and upper part of the condylar neck. Medially and laterally, the capsule is firm, in order to stabilize the mandible during movement. Anteriorly and posteriorly, the capsule is loose, in order to allow mandibular movements. Usually, only a thin lining of synovial fluid is present on the articular surfaces. Larger amounts of joint fluid usually are associated with painful internal derangement. The joint capsule and ligaments restrict excessive displacement of the mandible.
Movements
When the mouth is opened, the mandibular heads rotate around a common horizontal axis in combination with a gliding movement forward and downward in contact with the lower surface of the articular disks. Simultaneously, the disks move forward and downward on the temporal bones. This results from the attachments of each disk to the lateral and medial poles of the condyles and from the contraction of the lateral pterygoid. The forward gliding of the disk ceases when the posterior attachment to the temporal bone has been stretched to its limits. Thereafter, the further hinging and anterior gliding movement of each condyle continues until the condyle articulates with the most anterior part of the disk and the mouth is fully open.
As the mouth is closed, the movements are reversed. In the first phase, each mandibular head glides backward and then hinges on its disk, which is held forward by the lateral pterygoid. Finally, this relaxes to allow the disk to glide backward and upward on the temporal bone.
Blood supply
The deep temporal and masseteric branches of the maxillary artery and the branches of the superficial temporal artery, which arise from the external carotid artery, supply the TMJ. The blood vessels surround the joint in a network of fine branches. Venous drainage is via the superficial temporal, maxillary, and pterygoid plexus of veins.
Innervation of the TMJ
The capsule of the TMJ is innervated from a large branch of the auriculotemporal nerve. The anterior region of the joint is innervated from the masseteric nerve and from the posterior deep temporal nerve. The sensory innervation of the TMJ also appears to be via the fifth cranial nerve. The nerve fibers primarily follow the vascular supply and terminate as free nerve endings. Thus, the capsule, subsynovial tissue, and periphery of the disk are innervated. The articular cartilage and the central part of the disk contain no nerves. Myelinated and nonmyelinated nerves are seen in the TMJ. The retrodiskal bilaminar zone has a rich neurovascular supply and is the source of proprioception.
Microscopic anatomy
The TMJ differs from most other synovial joints of the human body by having its articular covering made of fibrous connective tissue instead of hyaline cartilage. The fibrous connective tissue covers the osseous components of the joint and merges with the periosteum at the periphery of the joint. The articular soft-tissue cover is avascular. The disk is fibrocartilage in which fibers predominate. The disk continues posteriorly into the tissue of the posterior disk attachment, which also has been termed the bilaminar zone. The tissue is composed of a loosely organized network of collagen fibers intermixed with a branching system of large elastic fibers, fat, and numerous blood vessels and nerves. In contrast to the disk, which is firm, the posterior attachment is readily deformable, and when the mouth is opened wide, it expands substantially.
Presentation
Typically, the patient with TMJ dysfunction is a young woman aged 20-40 years, presenting with a history of symptoms for 3-5 years. Misdiagnosis is not uncommon and may have occurred for several years, particularly during childhood and adolescence, because of the variety of poorly understood presenting symptoms. As a result, severe degenerative changes in the TMJ are observed even in children.
Symptoms of TMJ dysfunction include headache, craniofacial pain, jaw clicking, locking, facial deformity, unstable occlusion with or without pain, and various other symptoms, such as pressure, vertigo, and tinnitus referred to the ear, orbit, or calvarium.12 TMJ dysfunction secondary to internal derangement is a progressive disorder; it eventually results in ankylosis and osteoarthrosis of varying severity. The end result of the time-dependent, deforming changes is automeniscectomy, ideally with resolution of symptoms. TMJ internal derangement eventually reaches clinical quiescence after a clinical course in which disabling symptoms wax and wane, usually over a period of 6-10 years.
Preferred Examination
The initial examination used to image TMJ symptoms is usually plain radiographs/conventional tomography, because arthritic changes and congenital bone abnormality are visualized fairly well on plain films.13,14,15,16
MRI is the examination of choice, because it is the only modality that directly visualizes the meniscus and other soft-tissue joint components. Bony components are visualized better on computed tomography (CT) scans than on MRI scans.
At the authors' institution, planar radionuclide imaging using technetium-99m methylene diphosphonate/hydroxymethylene diphosphonate (99m Tc MDP/HMDP) and single-photon emission computed tomography (SPECT) scanning using99m Tc MDP/HMDP have been found to be sensitive methods for the diagnosis of TMJ disorders.17,18,19,20 The tendency is to use them as screening tests and, if normal, the authors usually do not proceed to other imaging techniques, such as MRI.
Arthrography/arthroscopy provide the criterion standard in the investigation of TMJ meniscus abnormality, but they are invasive and presently are used very selectively.21
Imaging allows accurate staging of internal derangement for operative planning. Patients in whom surgery is planned on 1 side frequently require evaluation of the asymptomatic joint, because silent TMJ dysfunction is frequent.
Although arthrography is said to be the criterion standard, MRI appears to be fast becoming the examination of choice. Unlike arthrography, MRI is noninvasive, requires no ionizing radiation for image acquisition, readily obtains multiplanar images in an infinite array of anatomic sections, allows direct visualization of soft-tissue components (including disk and joint structures), allows easy bilateral assessment, allows assessment of joint effusion and inflammation, and easily can image structures outside the joint, such as the joint capsule and muscles of mastication.5,6,7,22,23
As a primary imaging modality for internal derangement of the TMJ, CT scanning has fallen into disfavor because of the superiority of MRI, but it does have specialized imaging capabilities for assessing bone detail, for taking disk density measurements, and for permitting 3-dimensional (3D) assessment of congenital, traumatic, and postsurgical conditions involving the TMJ.
Relative advantages of MRI over CT scanning include a lack of ionizing radiation, the ability to perform primary imaging in multiple planes without imaging the patient, the superior image detail of articular soft-tissue components, the presence of fewer artifacts resulting from dense bone, and the ability to image bone marrow of the condyle.
Limitations of Techniques
A wide variety of abnormalities can present with signs and symptoms mimicking a possible problem in the TMJ. Studies have shown that physical examination alone is inaccurate in determining the status of the joint. Accuracy of the clinical diagnosis for the specific status of the joint is only 50-65%. The primary rationale for imaging the TMJ lies in the fact that mechanical internal derangement resulting from an anteriorly displaced disk and its concomitant pathology is treated differently from the multiple miscellaneous disorders of the TMJ and from myofascial pain dysfunction (MPD) syndrome. MPD is a common disorder affecting a considerable population, and clinical features include jaw pain, limited opening, headache, and earache.
Plain film and tomographic examinations are useful screening modalities. They are valuable for determining the presence of osseous changes and traumatic injury to the osseous components of the joint. Negative findings on plain film are most frequent but do not provide information regarding the presence or absence of soft-tissue disease.
Disadvantages of MRI include its high cost, its inability to visualize perforations of the posterior attachment or of the disk, and difficulty in assessing accurate jaw position for the initiation or adjustment of protrusive splint therapy.
Relative disadvantages of MRI compared with CT scanning include the high initial cost of the scanner, the fact that MRI is not widely available, the presence of claustrophobia in 10% of patients (who can be scanned in the prone position to increase acceptability), the length of scanning time, and the inferior images obtained of hard tissues.
Radionuclide imaging is a highly sensitive technique for evaluating the TMJ but is not specific; arthritis, tumor, inflammation, and trauma can give rise to similar appearances.
Arthrography is a sensitive and highly specific technique in the evaluation of TMJ meniscus abnormalities, but it is invasive and uncomfortable for the patient.
Differential Diagnoses
Gout
Osteochondroma and Osteochondromatosis
Septic Arthritis
Other Problems to Be Considered
TMJ osteoarthritis
TMJ synovitis
TMJ gout
TMJ osteochondromatosis
Temporomandibular tumors
Mandibular head avascular necrosis
Upper cervical spondylosis
Upper jaw dental pathology
Occlusion problems
Condylar hypertrophy
Mandibular asymmetry
Secondary osteoarthritis
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References
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Further Reading
Keywords
temporomandibular joint dysfunction, temporomandibular internal derangement, temporomandibular meniscal dysfunction, myofascial pain dysfunction syndrome, mandibular dysfunction, temporomandibular joint syndrome, craniomandibular disorders, temporomandibular disorders, TMJ
