Echo-intensity and fatty infiltration ultrasound imaging measurement of cervical multifidus and short rotators in healthy people: A reliability study

Background: In addition to muscle morphology, ultrasound imaging (US) could be a potential tool to determine muscle quality assessing the echo-intensity and using offline software to quantify the percentage of intramuscular fatty infiltration. Objective: To investigate intra- and inter-rater image measurement reliability of morphological (i.e., crosssectional area, perimeter) and echo intensity features (i.e., mean muscular echo intensity, fat echo intensity cut-offs, fatty infiltrates percentage estimation) of deep neck extensors in asymptomatic subjects. Methods: Brightness-mode images of the cervical spine at C4/C5 were acquired in 25 asymptomatic subjects (40% women, age: 24 years) by an experienced examiner. Cross-sectional area, perimeter and echo-intensity measures of cervical multifidus and short rotators were measured on two separate days (one-week apart) in a randomized order by two assessors. Intra-class correlation coefficients (ICC), standard error of measurement, minimal detectable change, and mean, absolute and percent errors were calculated. Results: Intra- (ICC3,1 0.800-0.989) and inter- (ICC3,2 0.841-0.948) examiner reliability of echo-intensity measures ranged from good to excellent. Women exhibited higher echo-intensity features than men. Intra-examiner reliability of morphological measures was excellent (ICC3,1 0.917-0.974) for multifidus and good-excellent (ICC3,1 0.868-0.987) for short rotators. Inter-examiner reliability of morphological measures also ranged from good to excellent (ICC3,2 0.765-0.965). Men exhibited higher CSA and perimeter than women. No side-to-side differences were observed in any ultrasound measure. Conclusion: This study found that intra- and inter-rater image analysis reliability of muscle morphology, mean echo intensity, and fatty infiltration quantification of cervical multifidus and short rotators at C4/C5 level was good-to-excellent in healthy subjects.