Validity of measuring distal vastus medialis muscle using rehabilitative ultrasound imaging versus magnetic resonance imaging.

UNLABELLED: Objective quantification of muscle size can aid clinical assessment when treating musculoskeletal conditions. To date the gold standard of measuring muscle morphology is magnetic resonance imaging (MRI). However, there's a growing body of evidence validating rehabilitative ultrasound imaging (RUSI) against MRI.
OBJECTIVE: This study aimed to validate RUSI against MRI for the linear measurements of the distal fibres of vastus medialis muscle in the thigh. Twelve healthy male participants were recruited from a local university population. The distal portion of their right vastus medialis was imaged with the participant in long-sitting, using MRI and RUSI whilst the leg was in extension and neutral hip rotation. Cross sectional area (CSA) and three linear measures were taken from the MRI and these were compared with the same linear measures from RUSI. Statistical analysis included comparison of MRI and RUSI measures using the paired t-test and intra-class correlation coefficients (ICC 3,1). Mean differences between the linear measures taken from the MRI and RUSI were -0.5 mm to 2.9 mm (95% confidence intervals -0.6-8.3 mm), which were not statistically different (p > 0.05) and were highly correlated (ICCs 3,1 0.84-0.94). Correlations between the three linear measurements and muscle CSA ranged from r = 0.23 to 0.87, the greatest being muscle thickness. Multiplying the linear measures did not improve the correlation of 0.87 found for muscle thickness. Linear measures of vastus medialis depth made using RUSI were shown to be as valid as using MRI. Muscle thickness measures using RUSI could be used within an objective assessment of this muscle.