Inter-Rater and Intra-Rater reliability of rehabilitative ultrasound imaging of core muscle thickness in individuals with Anterior Pelvic Tilt

Background & Objectives: Excessive lordotic curvature of the lumbar spine defines the phenomenon known as anterior pelvic tilt, which causes changes in posture, movement, and core muscle activation. Rehabilitative ultrasound imaging (RUSI) has been proposed as an effective means of evaluating muscle thickness both in static and dynamic states. The present study aimed to determine the intra-rater reliability of RUSI measurements of transverse abdominis (TrA), lumbar multifidus (LM), and gluteus maximus (GMax) muscle thickness at rest and during standardized contraction, and to determine the inter-rater reliability of these measurements in young adults with and without anterior pelvic tilt (APT). Methodology: The methodological reliability study was conducted at Al-Khumeini Trust Hospital, Lahore, Pakistan, between January 2023 and June 2023. Participants included forty-six volunteers between 18 and 28 years old, of which 23 subjects were diagnosed with APT and 23 had normal spinal alignment. Bilateral TrA, LM, and GMax thicknesses at rest and during contraction were measured twice in two assessment days by two independent raters who had more than five years of experience in RUSI. Intra-rater reliability was tested based on the measurements by the same rater in two different days, while inter-rater reliability was assessed between the two raters. ICC with 95% confidence interval, was used to quantify reliability. SEM and MDC95 were computed to assess absolute precision of the measurement. Results: The results showed consistent high intra- and inter-rater reliability in the thickness measurements of the TrA, LM, and GM muscles, with intraclass correlation coefficients between 0.930 and 0.998, suggesting that these measurements were highly consistent. SEM and MDC95 values indicated relatively small absolute measurement error, although the magnitude varied across muscle measurements. Conclusion: Standardized RUSI measurements of TrA, LM, and GMax muscle thickness demonstrated good-to-excellent intra-rater and inter-rater reliability in young adults with and without APT. These findings support the reproducibility of the measurement protocol under the conditions examined. Further studies are required to determine whether these reliability estimates are generalizable to older adults, symptomatic chronic low back pain populations, and examiners with different levels of RUSI experience.