Reliability of lumbar multifidus and iliocostalis lumborum thickness and echogenicity measurements using ultrasound imaging

Purpose: To establish the test–retest and inter-rater reliability of lumbar multifidus (LM) and iliocostalis lumborum (IL) muscle thickness and echogenicity as derived using ultrasound imaging. Methods: Ultrasound images of the LM and IL were collected from 11 healthy participants on two occasions, 1 week apart, by two independent assessors. Measures of LM and IL thickness and echogenicity were subject to test–retest and inter-rater reliability, which was assessed by calculation of an F statistic, the interclass correlation coefficient (ICC), the standard error of measurement, 95% confidence intervals and Bland–Altman plots. This study was given approval by The University of Melbourne Behavioural and Social Sciences Human Ethics Sub-Committee (ref: 1749845). Results: Assessors A and B showed good to excellent test–retest reliability for LM thickness (ICC3,3 A: 0.89 and B: 0.98), LM echogenicity (ICC3,3 A: 0.93 and B: 0.95) and IL echogenicity (ICC3,3 A: 0.87 and B: 0.83). Test–retest reliability for IL thickness was poor for Assessor A but excellent for Assessor B. Both assessors demonstrated excellent inter-rater reliability for LM thickness and echogenicity (ICC2,3: 0.79 and 0.94), but poor reliability for IL thickness and echogenicity (ICC2,3: 0.00 and 0.39). Conclusions: Inter-rater and test–retest reliability was excellent for LM but was less reliable for measures of the IL muscle.