MRI findings concerning the lateral pterygoid muscle in patients with symptomatic TMJ hypermobility.

Clinical studies have shown a close association between temporomandibular joint hypermobility (TMJH) and temporomandibular disorders (TMD). While pathological change of the lateral pterygoid muscle (LPM) is one of the most emphasized in studies of TMD, there have been no detailed clinical reports of the LPM studies using magnetic resonance imaging (MRI) in TMJH. This study investigates structural and pathological alterations involving the LPM in patients with TMJH using MRI. A retrospective analysis was made of high-field MRI images from 98 patients with TMJH. LPMs of 143 joints were analyzed. In 110 joints (77%), hypertrophy, atrophy, and contracture were found in the superior belly and/or the inferior belly of the LPM. Pathological changes were more frequently found in the superior rather than the inferior belly of the LPM. In the cases with abnormalities in both bellies of the LPM, hypertrophy of the inferior belly was usually found combined with other changes of the SBLPM. The results of this study indicated that the pathological changes of the LPM or MRI are not infrequent in patients with symptomatic TMJH.