temporomandibular joint dysfunction
Temporomandibular joint (TMJ) dysfunction is characterized by an abnormal relationship between the disc and the adjacent articular surfaces (condyle below with mandibular fossa and articular eminence above).
Epidemiology
TMJ dysfunction is far more common in women (F:M 8:1).
Clinical presentation
It is characterized by pain, clicking and functional restriction.
Pathology
Typically, the disc is displaced and does not maintain a normal relationship to the articular surfaces throughout the normal range of motion.
The direction of subluxation/displacement/dislocation can be in any direction, although anterior (unidirectional (i.e just anterior) anteromedial or anterolateral) is most common. It is important to realize that anterior displacement is very common in asymptomatic patients, seen in up to a third of joints. Of joints with an anteriorly displaced disc, only 20-30% are symptomatic. Initially it was thought that anterior displacement was congenital although now it appears to be acquired (ref needed).
On mouth opening there may be recapture/relocation/reduction of the disc to a normal position - or it may recapture in one plane but not another. Alternatively it may remain displaced.
Internal derangement occurs also secondary to abnormal disc morphology. Normally the disc should be biconcave fibrocartilaginous structure. Abnormal shape includes rounded, flattened, crumpled and perforated disc.
Radiographic features
MRI is the standard method of evaluation of TMJ. The study should include oblique sagittal spin and gradient echo T2 WIs on each TMJ separately both in open and closed mouth positions. Some institutes use PD instead of spin echo T2 sequence. Normally the disc is biconcave structure, returns low signal on all sequences, located between the condyle and temporal bone and its posterior band is located at 12 o'clock position with the angle between its posterior limit and vertical orientation of the condyle doesn't exceed 10.
Direct signs of disc displacement include abnormal orientation in open and closed mouth positions. Anterior disc displacement is the commonest abnormality and includes anterior disc displacement in closed mouth that reduces in open mouth and a non reduced anterior displacement. Posterior disc displacement occurs when the posterior band is displaced posteriorly and exceeds 1 o'clock position.
Stuck disc occurs when the disc fails to displace in open or closed mouth position and becomes fixed to the temporal bone due to adhesion.
Indirect signs of internal derangement include large joint effusion, rupture of retrodiscal layers, thickening of lateral pterygoid muscle attachment and osteoarthritic changes.
Treatment and prognosis
Treatment should be reserved for symptomatic patients:
- medical: NSAIDs
- orthodontic: intraoral splints
- malocclusion correction (protrusive splints)
- decrease pressure on the joint (flat splints)
- surgical
- for correction of displacement without recapture
- disc plication
- resection of the posterior band
- reattachment
- for decreased range of motion and "stuck disc"
- arthroscopic adhesionectomy
- arthroplasty has been tried with poor results
- reconstruction is also occasionally used: taking costochondral junction
- for correction of displacement without recapture
Complications
In symptomatic patients, most frequently in discs that do not recapture, inflammation of the joint with synovitis, joint effusion and bone marrow edema may be seen. Over time secondary osteoarthritic changes will develop with contour changes specially flattened condyle, osteophytes, subchondral sclerosis, joint space narrowing and subchondral cyst formation.
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