Objective: We sought to investigate the interrater and intrarater reliability of ultrasound and the minimum detectable change (MDC) for the trigger points (TrPs) active in the upper trapezius (UT) muscle in individuals with shoulder pain.

Methods: Forty individuals with shoulder pain were investigated for the presence of active TrPs in the UT muscle by means of ultrasound for the parameters of gray scale, muscle thickness of UT muscle at rest, and contraction and area of TrPs. The intrarater reliability was performed on 2 days, and interrater reliability on the same day. For the gray scale, the reliability was evaluated using the kappa coefficient (κ), while the other parameters were measured by the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and MDC.

Results: For the gray scale, the intrarater agreement was almost perfect (κ = 1.00) and the interrater agreement was substantial (κ = 0.75). The intrarater and interrater reliability were excellent for most of the parameters, except for the area of TrPs (intrarater: ICC = 0.71, substantial; interrater: ICC = 0.52, substantial). The MDC for intrarater reliability varied between 0.04 and 0.05 (SEM% between 2.4% and 38.87%), and that for interrater reliability ranged from 0.05 to 0.07 (SEM% between 3.18% and 55.10%), with a higher value for area.

Conclusion: Parameters such as gray scale, resting muscle thickness, and muscle contraction of the UT muscle, obtained through ultrasound, showed excellent intrarater and interrater reliability with low SEM%. The intrarater and interrater reliability for the area deserves a caveat regarding their use.

Author keywords: Myofascial Pain Syndromes; Ultrasonography; Trigger Points; Pain

Author affiliations: Department of Physical Therapy, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil.

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