Thickness of the middle trapezius muscle measured by rehabilitative ultrasound imaging: description of the technique and reliability study

A technique is described for measuring the thickness of the middle trapezius muscle using rehabilitative ultrasound imaging (RUSI). A test-retest study was employed to investigate the reliability of the technique in a convenience sample of 16 asymptomatic participants aged 20-41 (12 women). The middle trapezius muscle was imaged using RUSI with participants in a standardized sitting position. The principal investigator took measurements on two consecutive days to examine intra-rater reliability, and two additional investigators took measurements on the second day to investigate inter-rater reliability of the measurement technique. Reliability was examined using intra-class correlation coefficients (ICC), standard error of measurement (SEM), and Bland and Altman plots. The results demonstrated that inter-rater reliability was good between raters (ICC₂,₃ = 0.81, SEM = 0.94 mm) and was moderate for the same rater between days (ICC₃,₂ = 0.67, SEM = 1.0 mm). This study demonstrates that RUSI can be used reliably to measure muscle thickness of the middle trapezius muscle following the procedure described.