Study design: Exploratory and reliability study.
Background: Shoulder dysfunction is common and often difficult to diagnose and treat. The trapezius muscle is an important stabilizer and primary mover of the scapula. The potential use of rehabilitative ultrasound imaging (RUSI) to evaluate scapular muscle function warrants investigation.
Objectives: To establish a procedure for imaging the thickness of the lower trapezius muscle and to examine reliability within and among investigators.
Methods: In 16 asymptomatic subjects (12 female, 4 male), aged 20 to 41 years, 3 investigators used RUSI to measure the thickness of the left lower trapezius muscle with the subject at rest in prone. Investigator 1 took 3 images on each of 2 days, while the other 2 investigators took 2 images each on the second day. All measurements of lower trapezius muscle thickness were made off-line, at a point 3 cm lateral to the lateral edge of the spinous processes. To also obtain within-scan reliability, 1 image taken by investigator 1, once displayed on the scanner's screen, was measured 3 times. Investigator 1 also measured lower trapezius muscle thickness 1 cm medial to this site. Reliability was examined using intraclass correlation coefficients (ICC) and the Bland and Altman plot.
Results: The intrarater within-scan reliability at the lateral site was ICC3.3 = 0.99 (95% CI: 0.98 to 1.0). The intrarater between-scan reliability (within-day) at the lateral site, medial site, and combined sites (mean of medial and lateral) were ICC3.3 = 0.96 (95% CI: 0.90 to 0.98), ICC3.2 = 0.90 (95% CI: 0.78 to 0.96), and ICC3.2 = 0.99 (95% CI: 0.99 to 1.0), respectively. Intrarater (between-day) reliability was good for the lateral site and combined sites (ICC3.3 = 0.91, 95% CI: 0.74 to 0.96, and ICC3.3 = 0.90, 95% CI: 0.70 to 0.96, respectively) and moderate for the medial site (ICC3.3 = 0.89, 95% CI: 0.68 to 0.96). Interrater reliability (among investigators) was also moderate (ICC2.2 = 0.88, 95% CI: 0.73 to 0.96). Mean lower trapezius muscle thickness was approximately 3.1 mm (SD, 0.8 mm).
Conclusion: Thickness of the lower trapezius muscle can be measured reliably with RUSI.