Quantitative evaluation of the masseter and temporalis muscles with shear wave elastography in MRI-verified temporomandibular disorders

Objective imaging biomarkers for temporomandibular disorders (TMD) remain limited, particularly for quantitative assessment of masticatory muscle alterations. This prospective study aimed to evaluate the thickness and stiffness of the masseter and temporalis muscles using shear wave elastography (SWE) in patients with MRI-verified TMD.

A total of 113 participants, including 48 patients with clinically and MRI-confirmed TMD and 65 healthy controls with normal bilateral temporomandibular joint MRI findings, were prospectively enrolled. Bilateral masseter and anterior temporalis muscles were evaluated at rest. Muscle thickness was measured using B-mode ultrasonography, and stiffness was quantified by SWE using a standardized 2-mm region of interest. Interobserver reliability was assessed using the intraclass correlation coefficient (ICC), and diagnostic performance was evaluated by receiver operating characteristic (ROC) analysis.

Compared with healthy controls, patients with TMD demonstrated significantly greater thickness and stiffness in both the masseter and temporalis muscles (all p < 0.001). No significant differences were observed between patients with disc displacement with reduction and those without reduction. Interobserver agreement was excellent for all measurements (ICC ≥ 0.90). Among all parameters, masseter muscle stiffness showed the highest diagnostic performance (AUC = 0.982), with an optimal cut-off value of 19.03 kPa, yielding 91.7% sensitivity and 98.5% specificity for identifying TMD.

TMD is associated with significant structural and biomechanical alterations in both the masseter and temporalis muscles. Quantitative SWE, combined with MRI verification, provides a reproducible and noninvasive imaging approach with excellent diagnostic performance for the evaluation of TMD.