According to the meta-analysis of Su et al. (2018), with MRI being used as the reference standard, the added diagnostic value of ultrasound (US) for ruling in and ruling out disc displacement (DD) in the temporomandibular joint (TMJ) is sufficient for its use in the decision-making. After sufficient training and calibration of operating and interpretation, US can be considered as a relevant imaging tool to supplement clinical examination in patients with suspected DDs. Combined static and dynamic examinations using high-resolution US should be preferred.
The most frequent cause of TMJ dysfunction is DD, which is an abnormal relationship between the disk and the condyle. Anterior displacement with reduction is defined as DD with the mouth closed that reduces (with a click) to the normal relationship at some time during opening. The mandible deviates to the affected side on opening until the click occurs and then returns to the midline. This situation may worsen from intermittent locking of the disk to anterior DD without reduction (closed lock), the dislocated disk acting as a mechanical obstruction to opening and translation of the condyle, leading to a marked decrease in mandible opening on the affected side and a variable degree of pain.