Ultrasound Backscatter Parameters to Assess Upper Trapezius Muscle Hypertonicity in Adults

Objectives To investigate the feasibility of ultrasound backscatter parameters in assessing upper trapezius muscle (UTM) hypertonicity. Methods We prospectively measured pixel intensity on B-mode ultrasound images of UTM and adjacent subcutaneous tissue (SUBC) using Image J histogram, and calculated backscatter reduction rate and anisotropy following beam steering at 5°, 10°, 15°, and 20° from 0°. We analyzed differences in backscatter parameters of UTM and SUBC between three age groups using one-way analysis of variance (ANOVA), between normal and hypertonic UTMs using paired t-test, diagnostic performances of backscatter parameters for determining ≥ mild hypertonic UTM using area under receiver operating characteristic curve (AUC), and inter- and intra-observer reliability in measuring pixel intensity using intraclass correlation coefficient (ICC) and Blant-Altman analysis. Results We recruited 125 adult subjects (39 with normal UTM, 86 with hypertonic UTM) in three age groups (young age: 18-44y; middle age: 45-64y; old age: ≥65y). Differences in backscatter parameters between normal and hypertonic UTM were significant in young and middle-aged groups (p< 0.01) but not in old-aged group ( p >0.05). AUC of muscle backscatter reduction rate at beam steering 20° for determining ≥ mild hypertonicity was 0.89, 0.80, and 0.64 in young, middle-aged, and old-aged participants, respectively. ICCs of observer reliability for measuring pixel intensity were > 0.80. Conclusions The muscle backscatter reduction rate at beam steering 20° can distinguish hypertonic muscles from normal muscles in young and middle-aged with good intra- and inter-operator reliability. Muscle backscatter reduction rate in adults decreases with aging and the occurrence of hypertonicity.