Impact of forearm pronation on ultrasound-measured forearm muscle thickness in children and adolescents

Abstract

Background and Aim: It was unknown whether ultrasound-measured forearm muscle thickness was impacted by pronation of the forearm. The aim of this study was to investigate the influence of forearm pronation on two forearm muscle thicknesses (MT-ulna and MT-radius). Participants and Methods: Fourteen healthy children and adolescents sat on a chair with their right arm comfortably on a table, and their hands were fixed to the board with elastic bands. The probe was placed perpendicularly over the forearm, and the angle of the board was then pronated in 5° increments from -10° to 30°. The average value of the two measures at each angle was used. Results: There was evidence that MT-ulna differed across measurement sites (F = 51.086, P < 0.001). For example, the values of the MT-ulna were 2.58 (SD 0.40) cm in standard position (0°), 2.56 (SD 0.41) in -10°, 2.62 (SD 0.41) in 10°, 2.65 (SD 0.42) in 20°, and 2.71 (SD 0.43) in 30°. Follow-up tests found that all sites differed from each other except for -10° and -5° (P = 0.155) and 10° and 15° (P = 0.075). There was also evidence that the MT-radius differed across measurement sites (F = 22.07, P < 0.001). Follow-up tests found that many but not all sites differed from each other. Conclusion: Our results suggest that MT-ulna increases and MT-radius decreases due to forearm pronation from the standard position (0°). When determining the forearm position using the 95% limits of agreement, we recommend the forearm position within ±5° of the standard forearm position when measuring forearm MT.