Discriminative and reliability analyses of ultrasound measurement of abdominal muscles recruitment

Rehabilitative ultrasound imaging has a great potential to be used as a tool in the assessment of trunk muscle function in patients with low back pain (LBP). However, a further investigation of the discriminative ability of this tool as well as the effect of operators' levels of training on reliability is warranted. Discriminative analysis of ultrasound and electromyography (EMG) measurements of transversus abdominus (TrA), obliquus internus (OI), and obliquus externus (OE) muscles function between people with and without LBP and the effect of operator's training on reliability of TrA muscle function of chronic LBP patients were conducted. For the discriminative study, measurements were collected from 10 subjects with LBP and 10 matched controls during isometric low load tasks with their limbs suspended. For the reliability study, in stage 1 the reliability of single ultrasonographic static images involved 4 operators (1 trained and 3 non-trained), whereas, in stage 2, two operators (1 trained and 1 non-trained) were used to determine the reliability of TrA thickness change. Methods used in the statistical analysis were pearson correlation and receiver operating characteristic curve for the discriminative study and intraclass correlation coefficient (ICC) for the reliability study. While ultrasound measures of OE muscle function showed poor association with EMG (r = 0.28, p = 0.22), TrA and OI function showed moderate to excellent association (TrA: r = 0.74, p < 0.000; OI: r = 0.85, p < 0.000). Ultrasound and EMG measures of TrA and OI function discriminated LBP patients from controls. Reliability of the assessment of TrA function with a trained operator (ICC = 0.92; 95% CI: 0.81-0.97) was substantially higher than a non-trained one (ICC = 0.44; 95% CI: -0.41-0.78). In conclusion, ultrasound measures of deep trunk function is a valid discriminative tool in LBP but highly dependent on operator's level of training.