Intra-articular pressure measurements in patients with suddenly developing, severely limited mouth opening.

A condition of sudden, severe, and persistent limited mouth opening, which readily responds to arthrocentesis, is postulated to be the effect of a vacuum between disc and fossa in the upper compartment of the temporomandibular joint. In 16 patients with this condition, the negative intra-articular pressure was found to be significantly lower (mean, -82.6 +/- 25.4 mm Hg) than in the control group (mean, -7.7 +/- 2.5 mm Hg) (P less than .0001). It is suggested that the process underlying the vacuum effect starts with persistent pressure (eg, clenching) resulting in the viscoelastic disc being pressed flat against the fossa. Immediately on cessation of the pressure, the disc resumes its natural biconcave shape, but its rims remain fastened to the fossa. The consequent increased negative pressure in the closed space created firmly anchors the disc to the fossa and any attempt to elicit condyle and disc sliding will only stretch the joint capsule and cause pain. This, in turn, will reflexly prevent the pterygoid muscle from exerting sufficient force to pull the disc and thus release the vacuum. This chain of events may account for the severe and persistent limitation in jaw movement and for the easy reversal of the condition by simple nonsurgical treatment.