Sideways dislocation of the temporomandibular joint meniscus: the edge sign.

Seventy temporomandibular joint arthrograms of 49 patients with symptoms of internal joint derangement were reviewed. Twenty-three of these arthrograms (33%) were abnormal but atypical for anteriorly dislocated meniscus. The lower temporomandibular joint space had a well-defined edge located inferiorly, which was attributed to pressure from a sideways-dislocated meniscus. We called this appearance the "edge sign." Seven patients with radiologically apparent sideways dislocation were operated on. The meniscus was dislocated laterally in six and medially in one. The incidence of irreducibility and perforation was higher in sideways-dislocated than in anteriorly dislocated menisci.