Ultrasound Video Recordings Enable Intra-rater Reliability of Muscle Size Measurements of the Toe Flexor Muscles

Abstract

Ultrasound (US) imaging is being utilized in orthopedic, sport, and exercise research. It is a cost-effective way to assess cross-sectional area (CSA) and thickness of muscles in vivo; it can be used in research and clinical settings to monitor muscle changes. PURPOSE: To determine intra-rater reliability in measuring separate consecutive US still images obtained from video recordings of the lateral toe flexors: flexor digitorum longus (FDL), flexor digitorum brevis (FDB), and quadratus plantae (QP). METHODS: Videos were taken starting from a relaxed state to a contracted state and back to the relaxed state for the CSA of the FDL, FDB, and QP and thickness of the QP. A trained individual, using a 10 MHz linear probe (GE LogiqP6), recorded US videos of the FDL, FDB, and QP muscles of 12 feet. The videos for the FDL were taken at a point 50% distal from the medial knee joint line to the inferior tip of the medial malleolus with the probe held perpendicular to the shaft of the leg. For the videos of the FDB and QP, the probe was held perpendicular to the sole of the foot in line with the navicular tuberosity. Each participant was instructed to flex their toes and videos of the contraction cycle were recorded. The video recording was used in order to more easily differentiate the fascial borders of the muscles of interest at the time of measurement. Using the ultrasound machine’s internal software, 2 separate still-shots of the muscles at rest were saved from the recorded videos to make calculations of either the CSA or thickness. Each individual image was measured by the same rater and the rater was blinded to each measurement value. The measurements were made one right after the other. RESULTS: The ICC3,1 for the measurement reliability of CSA of the FDL was 0.985, CSA for the FDB was 0.996, and CSA QP was 0.978, while the ICC3,1 for QP thickness was 0.998. CONCLUSIONS: Excellent intra-rater reliability was achieved to assess muscle CSA and thickness when video recordings of the FDL, FDB, and QP during the contraction cycle were utilized to obtain more accurate estimates of the fascial borders than by using still images alone. The rater was also accurate at finding images within the video that represented the relaxed state.