2D shear wave elastography for the assessment of quadriceps entheses—a methodological study

Objective To establish the scanning protocol for 2-dimensional shear wave elastography (SWE) on normal entheses by investigating the possible confounding factors that may increase the variability of measured elasticity. Material and methods 30 normal quadriceps entheses were scanned using SWE to compare the stiffness and coefficient variation by changing the ultrasonic coupling gel thickness, knee position, region of interest size, and scanning plane. Results No significant difference in median shear wave velocity (SWV) was observed in different coupling gel thicknesses. The median SWV was higher in the knee flexion position than in the extended position ( p < 0.001). Increased knee flexion led to stiffer quadriceps enthesis and higher SWV ( ρ = 0.8, p < 0.001). The median SWV was higher when the diameter region of interest was 4.0 mm than 2.0 mm ( p = 0.001). The median SWV was higher in the transverse plane than in the longitudinal plane ( p < 0.001). Strong correlation was found between SWV and the degree of the shear wave to muscle fiber direction ( ρ = 0.8, p < 0.001). The coefficient variation was lower in a gel thickness of 2.5 cm, with an extended knee, a region of interest of 2.0 mm, and a longitudinal plane ( p > 0.05). For interobserver reliability for the proposed protocol, the intraclass correlation coefficients was 0.763. Conclusion In this study, we determined supine position with the knee extended; using 2.0 mm diameter region of interest and image acquisition at the longitudinal plane with thicker layer coupling gel seems most appropriate to reliably image healthy quadriceps entheses with SWE.