The Intra-Rater Reliability of Ultrasonography for the Measurement of Lumbar Multifidus and Erector Spinae Thickness in Different Positions in People with and without Active Extension-Related Non-Specific Low Back Pain

Background: The paraspinal muscles, including multifidus (MF) and erector spinae (ES) play key roles in the stability and movement of the lumbar spine. This study aimed to determine the intra-rater reliability of the ES and MF muscle thickness measures of the rehabilitative ultrasound imaging (RUSI) in people with active extension pattern (AEP) non-specific chronic low back pain and controls Methods: Fifteen females with AEP and 19 controls participated in this test-retest intra-rater reliability study, including two different testing sessions performed in four to seven days apart. The primary (raw) and derived (normalized) measures of the L4 MF and ES muscles'thickness were examined in three different positions (prone, sitting, and standing) on both days. A two-way mixed average of intra-class correlation coefficient (ICC3, K) with confidence interval (CI = 95%) was used to determine the relative reliability. The standard error of measurement (SEM) and minimal detectable change (MDC) values at a CI of 95% were computed to examine the absolute reliability. Results: The ICC values for the primary thickness of the L4 ES and MF muscles were from 0.85 to 0.91, except for MF muscle thickness in standing (ICC = 0.67) and sitting (ICC = 0.66) positions. The ICC values for derived data were lower in both groups. The SEM and MDC values were small enough to confirm the absolute reliability of the primary data. Conclusion: This study supports the use of RUSI for examining the primary measures of the L4 MF and ES muscles in asymptomatic and AEP participants, but it should be used cautiously for assessing the derived measures.