Ultrasonographic assessment of local cross-sectional dimensions of masseter muscle sites: a reproducible technique?

Local cross-sectional dimensions (LCSDs) of masseter muscle sites may now be measured non-invasively using ultrasonography. The purpose of the present study was to determine (i) whether the muscle site may affect LCSD measurements and (ii) whether measurements made at identical sites may be reproducible. The study included 17 patients who had signs and symptoms of temporomandibular disorders (TMD). Bilateral ultrasonographic investigation was performed with a linear (B-scan) 7.5 MHz small-part transducer to visualize the antero-superior, antero-inferior, medio-superior, medio-inferior, postero-superior, and postero-inferior sites of the masseter muscle. Measurements were made in two sessions with a time interval of at least five minutes. Data were analysed for reproducibility by using the intraclass correlation coefficient (ICC) and the method error (ME). Muscle site had no significant effect on muscle measurements (P = 0.090). Measurements from the various side-related sites did not differ significantly (P = 0.425). Measurements recorded at a given site were consistent across the testing sessions (P = 0.605). The muscle site with highest reproducibility was the medio-inferior site (ICC = 0.92; ME = 6.4%). The data suggest that ultrasonography is a reproducible method for measuring LSCDs of the masseter muscle.