Repeatability of ultrasonographic median nerve measures

In this study we investigated the reliability of ultrasound in measuring median nerve characteristics including cross-sectional area (CSA), flattening ratio (FR), swelling ratio (SR), and mean grayscale. Generalizability theory was used to assess inter- and intrarater reliability using the dependability coefficient (phi), normalized standard error of measurement, and normalized minimum detectable change (MDC(NORM)) for multiple study design protocols. Interrater reliability was generally moderate. Intrarater reliability was mostly good (phi > 0.876) when using a single image, captured on one occasion, and being read once. Intrarater MDC(NORM) ranged from 3.8% to 6.2% for all CSA measures and SR. Using multiple images and/or readings at multiple occasions did not appreciably improve reliability measures. Ultrasound is a reliable tool for measuring median nerve characteristics. We recommend that a single evaluator capture all images for protocols aimed at quantifying median nerve ultrasound measures. We believe an appropriately designed protocol can utilize ultrasound to accurately assess changes in median nerve characteristics after activity.