Reliability of Rehabilitative Ultrasound Imaging of the Transversus Abdominis and Lumbar Multifidus Muscles

Objectives: To evaluate the intraexaminer and interexaminer reliability of rehabilitative ultrasound imaging (RUSI) in obtaining thickness measurements of the transversus abdominis (TrA) and lumbar multifidus muscles at rest and during contractions. Design: Single-group repeated-measures reliability study. Setting: University and orthopedic physical therapy clinic. Participants: A volunteer sample of adults (N=30) with current nonspecific low back pain (LBP) was examined by 2 clinicians with minimal RUSI experience. Interventions: Not applicable. Main Outcome Measures: Thickness measurements of the TrA and lumbar multifidus muscles at rest and during contractions were obtained by using RUSI during 2 sessions 1 to 3 days apart. Percent thickness change was calculated as thickness(contracted)-thickness(rest)/thickness(rest). Intraclass correlation coefficients (ICC) were used to estimate reliability. Results: By using the mean of 2 measures, intraexaminer reliability point estimates (ICC(3.2)) ranged from 0.96 to 0.99 for same-day comparisons and from 0.87 to 0.98 for between-day comparisons. Interexaminer reliability estimates (ICC(2,2)) ranged from 0.88 to 0.94 for within-day comparisons and from 0.80 to 0.92 for between-day comparisons. Reliability estimates comparing measurements by the 2 examiners of the same image (ICC(2.2)) ranged from 0.96 to 0.98. Reliability estimates were lower for percent thickness change measures than the corresponding single thickness measures for all conditions. Conclusions: RUSI thickness measurements of the TrA and lumbar multifidus muscles in patients with LBP, when based on the mean of 2 measures, are highly reliable when taken by a single examiner and adequately reliable when taken by different examiners.