Assessment of Masseter Muscle Stiffness by Ultrasound Elastography in Patients with Temporomandibular Disorders: A Systematic Review and Meta-analysis

Abstract To assess the stiffness of the masseter muscle in patients with temporomandibular disorders (TMDs) by shear wave elastography and compare the measurements of masseter muscle stiffness at rest and during muscle contraction. A systematic review and meta-analysis following PRISMA guidelines included studies on masseter muscle stiffness via shear wave elastography in TMD patients, analyzing resting and contracted states separately. Standardized mean differences (SMDs) were pooled with a random-effects model. Bias was evaluated using QUADAS-2, heterogeneity and prediction intervals were assessed, and significance was set at p < 0.05. For the resting state, five studies (n = 137 in each group) were included. The pooled SMD was 3.16 (95% CI: −0.70 to 7.03, p = 0.11), with high heterogeneity (I2 = 96%). In the contracted state, four studies (n = 111 experimental, 113 control) showed a significant difference with an SMD of 1.20 (95% CI: 0.58 to 1.83, p < 0.01), and moderate heterogeneity (I2 = 71%). Prediction intervals indicated more consistent findings during contraction. Shear wave elastography, particularly when applied during muscle contraction, is effective in distinguishing masseter muscle stiffness in patients with TMD. Contracted-state measurements yield statistically significant and more consistent results compared with the resting state, supporting the clinical relevance of shear wave elastography in TMD diagnostics.