Internal Temporomandibular Joint (TMJ) Derangement
(See also Overview of Temporomandibular Disorders.)
Internal derangements may occur if the morphology of the disk is altered and the diskal ligaments become elongated. The severity of the derangement depends on the extent of the disk and ligament changes. If the disk remains anterior to the condyle, the derangement is said to be without reduction. Restricted jaw opening (locked jaw) and pain in the ear and around the temporomandibular joint may result. If at some point in the joint’s excursion the disk returns to the head of the condyle, the derangement is said to be with reduction. Nonpainful derangement with reduction occurs in about one third of the population at some point.
All types of derangement can cause capsulitis (or synovitis), which is inflammation of the tissues surrounding the joint (eg, tendons, ligaments, connective tissue, synovium). Capsulitis can also occur spontaneously or result from arthritis, trauma, or infection.
Disk derangement with reduction often causes a painless clicking or popping sound when the mouth is opened. Pain may be present, particularly when chewing hard foods. Patients are often embarrassed because they think others can hear noise when they chew. Indeed, although the sound seems louder to the patient, others can sometimes hear it.
Disk derangement without reduction usually causes no sound, but maximum opening between the upper and lower incisors is reduced. Pain and a change in the patients' perception of their bite generally result. It usually manifests acutely in a patient with a chronically clicking joint; about 8 to 9% of the time, the patient awakens unable to open the jaw fully.
In a small percentage of patients, the symptoms of disk derangement without reduction spontaneously resolve after 6 to 12 months.
Capsulitis results in localized joint pain, tenderness, and, sometimes, restricted opening.
Diagnosis of disk derangement with reduction requires observation of the jaw when the mouth is opened. When the jaw is opened > 10 mm (measured between the incisal edges of the upper and lower incisors), a click or pop is heard, or a catch is felt, as the disk pops backward over the head of the condyle. The condyle remains on the disk during further opening. Usually, another, more subtle (reciprocal) click is heard during closing when the condyle slips over the posterior rim of the disk and the disk slips forward.
Diagnosis of disk derangement without reduction requires that the patient open as wide as possible. The opening is measured, and gentle pressure is then exerted to open the mouth a little wider. Normally, the jaw opens about 45 to 50 mm; if the disk is deranged, it will open about ≤ 30 mm. Closing or protruding the jaw against resistance worsens the pain.
MRI is sometimes done to confirm presence of a disk derangement or to determine why a patient is not responding to treatment.
Capsulitis is often diagnosed based on a history of injury or infection along with exquisite tenderness over the joint and by exclusion when pain remains after treatment for myofascial pain syndrome, disk derangement, arthritis, and structural asymmetries. However, capsulitis may be present with any of these conditions.
Disk derangement with reduction does not require treatment if the patient can open reasonably wide (about 40 mm or the width of the index, middle, and ring fingers) without discomfort. If pain occurs, mild analgesics, such as nonsteroidal anti-inflammatory drugs (NSAIDs; ibuprofen 400 mg orally every 6 hours), can be used. Some patients benefit from doing passive jaw-motion exercises using commercially available mechanical devices.
If onset is < 6 months, an anterior repositioning appliance may be used to move the mandible forward, repositioning the condyle on the disk. This oral appliance is horseshoe-shaped, hard, transparent acrylic (plastic) made to fit snugly over the teeth of one arch. Its occlusal surface is designed to hold the mandible forward when the jaw closes on the appliance. In this position, the disk is always on the head of the condyle (ie, the normal condyle-disk relationship is reestablished). The oral appliance is gradually adjusted to allow the mandible to move posteriorly. If the disk stays with the condyle, the disk is said to be captured. However, the longer the disk is displaced, the more deformed it becomes and the less likely its repositioning will succeed. Surgical plication of the disk may be done, with variable success.
Disk derangement without reduction may not require treatment other than analgesics. Oral appliances may help if the articular disk has not been significantly deformed and may reduce forces on the retrodiskal tissues, thereby encouraging adaptation of these tissues. However, long-term use may result in irreversible changes in oral architecture. In some cases, the patient is instructed to slowly stretch the disk out of position, which allows the jaw to open normally. Various arthroscopic and open surgical procedures are available when conservative treatment fails.
Capsulitis is initially treated with NSAIDs or oral corticosteroids, jaw rest, and muscle relaxation. Sometimes an oral appliance worn during sleep or while awake may be used briefly until the inflammation decreases. If these treatments are unsuccessful, corticosteroids may be injected into the joint, or arthroscopic joint lavage and debridement are used.
The articular disk is displaced anteriorly due to abnormal jaw mechanics; it may remain displaced (without reduction) or return (with reduction).
Disk displacement with reduction typically manifests with clicking/popping and pain with jaw use (such as chewing).
Disk displacement without reduction does not manifest with clicking/popping, but maximum jaw opening is limited to ≤ 30 mm.
Surrounding tissues may become painfully inflamed (capsulitis).
Analgesics, oral appliances, and passive jaw-motion exercisers often help, but surgery is occasionally required.
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