Estimating the volume of the First Dorsal Interossoeus using ultrasound

Accurate in vivo estimation of muscle volume is important as it indicates the amount of power a muscle can produce. By tracking muscle volume changes in vivo, a muscle's response to disease or rehabilitation training can be quantified. The purpose of this study was to validate the use of imaging ultrasound to estimate the volume of a small muscle, specifically the First Dorsal Interosseous (FDI) muscle. The perimeter of the FDI was imaged using ultrasound in 22 cadaver hands. For each FDI, serial cross-sectional areas were determined by manual digitization, volumes were then estimated using the Cavalieri principle. The muscles were then dissected from the cadavers, and muscle volume was determined via the water displacement method. The water displacement measures of muscle volumes were used as the criterion, and compared with those estimated via ultrasound. A Bland-Altman plot illustrated that all measures fell within the 95% confidence interval, with no statistical evidence of changes in measurement accuracy with size of specimen, or of a constant deviation in the accuracy of estimated volumes. For superficial muscles these results indicate that ultrasound imaging is an accurate method for determining muscle volumes in vivo even for a relatively small muscle (volume ∼4 mL).