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.