To provide a detailed description of the ultrasound (US) scanning protocol to measure the muscle thickness in the forearm and to test its feasibility and interobserver reliability.
Four rheumatologists trained in musculoskeletal US carried out the examinations in 45 subjects (30 consecutively enrolled patients and 15 healthy subjects). Each of the four rheumatologists took two measurements of each forearm (radial muscle thickness and ulnar muscle thickness) and the time needed to complete the bilateral US assessment was recorded.
The mean time required to acquire all measurements in each subject was less than four minutes. We found an excellent interobserver reliability of the proposed scanning protocol, with an intraclass correlation coefficient (ICC) among the four sonographers of 0.97 (CI 0.95-0.98) for the right ulnar muscle thickness, an ICC of 0.97 (CI 0.94-0.98) for the left ulnar muscle thickness, an ICC of 0.93 (CI 0.89-0.96) for the right radial muscle thickness and an ICC of 0.95 (CI 0.91-0.97) for the left radial muscle thickness.
The results of this study provide evidence in favour of interobserver reliability and feasibility of US measurement of the forearm muscle thickness.