Influence of transducer orientation on shear wave velocity measurements of the iliotibial band

Tissue anisotropy influences estimation of mechanical properties of connective tissues, such as the iliotibial band (ITB). This study investigated the influence of ultrasound transducer rotation and tilt on shear wave velocity (SWV, an index of stiffness) measurements of the ITB and the intra-rater repeatability of SWV measurements in the longitudinal direction. SWV was measured unilaterally (dominant limb) using ultrasound shear wave elastography in the middle region of the ITB in supine at rest (20-25 degrees knee flexion) in ten healthy volunteers (4 females). A 3 dimensional video system provided real-time feedback of probe orientation with respect to the thigh. Measurements were made at 10 degrees increments of probe rotation, from longitudinal to transverse alignment relative to the approximate direction of ITB fibres, and 5-10 degrees tilts about the longitudinal and sideways axes of the transducer. One-way repeated measures ANOVA compared SWV between angles and tilts. Intraclass correlation coefficients (ICCs) and standard error of measurement (SEM) were used to calculate repeatability for two to five (longitudinal only) repetitions. SWV was greatest when the transducer was aligned to ITB fibres (longitudinal: 10.5 +/- 1.7 m/s) and lowest when perpendicular (transverse: 5.8 +/- 2.4 m/s). Compared to longitudinal alignment, SWV decreased significantly (p < 0.01) when the transducer was rotated 20 degrees or more. Tilted measurements did not differ between angles. Intra-rater repeatability was excellent with the average of two measurements (ICC = 0.99, 95% CI 0.95, 0.99; SEM = 0.31 m/s). These findings show that SWV changes with orientation relative to fibre direction. Transducer orientation requires careful control to ensure comparable measures. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The orientation of the ultrasound transducer significantly affects the measurement of stiffness of the iliotibial band, with stiffness being highest when aligned with the band fibers and lowest when perpendicular. There was a significant decrease in stiffness when the transducer was rotated 20 degrees or more. Tilted measurements did not differ between different angles, and intra-rater repeatability was excellent.