Abstract

The fact that the lateral pterygoid muscle (LPM) and related symptoms play an important role in temporomandibular disorders (TMD) is widely recognized. In the study reported here, the LPM was investigated by magnetic resonance imaging (MRI) of patients with TMD. The visibility of the LPM in MRI with different projections was analyzed and a new imaging projection, condyle-the lateral pterygoid muscle projection (CLPM), for the LPM in MRI was introduced. Normal and abnormal findings of the LPM was compared with clinical symptoms of TMD.

Compared with sagittal imaging of temporomandibular joint (TMJ), CLPM images and most of the oblique sagittal imaging were able to show the LPM clearly. Hypertrophy, atrophy and contracture of the LPM were found in TMJs either with disc in normal position or with disc displacements. Pathological changes of the superior belly and hypertrophy of the inferior belly combined with various pathological changes of the superior belly were the most frequently observed abnormal imaging findings of the LPM in TMD. The pathological changes of the LPM were associated with the main clinical symptoms of TMD. In patients with symptomatic condyle hypermobility, the pathological changes of the LPM and related symptoms were associated with the clinical symptoms of TMJs with disc in normal position. The imaging abnormalities of the LPM were common in TMJs with disc displacements and seemed to be fewer in condyle hypomobility cases in TMJs with anterior disc displacement with non-reduction (ADDnr). However, normal imaging of the LPM was also found in TMJs with severe osteoarthritic changes and disc displacement.

The recognition of muscle alterations may lead to a more specific diagnosis and improve the understanding of the clinical symptoms and disease pathophysiology of TMD.