Ultrasonic strain elastography for detecting abnormalities in the supraspinatus tendon: an intra- and inter-rater reliability study

Objectives The reliability of ultrasonic strain elastography (SEL) used to detect abnormalities in the supraspinatus tendon is unclear. Thus, the aim of this study was to investigate the reliability of SEL in the supraspinatus tendon. Design An intra-rater and inter-rater reliability study. Setting A single-centre study conducted at the University of Southern Denmark. Participants Twenty participants with shoulder pain and MRI-verified supraspinatus tendinosis and 20 asymptomatic participants (no MRI). Primary and secondary outcome measures Raw values (RAW) and ratios (deltoid muscle (DELT) and gel pad (GEL) as reference tissues) were calculated and mean values of measurements from three regions of the supraspinatus tendon were reported. Colour scale ratings and number of yellow/red lesions from the three areas were also included. Results Intra-rater reliability showed intraclass correlation coefficients (ICCs) for RAW, DELT and GEL: 0.97 (minimal detectable change (MDC): 0.28 (6.36% of the mean)), 0.89 (MDC: 2.91 (20.37%)) and 0.73 (MDC: 1.61 (58.82%)), respectively. The ICCs for inter-rater reliability were 0.89 (MDC: 0.47 (10.53%)), 0.78 (MDC: 3.69 (25.51%)) and 0.70 (MDC: 1.75 (62.63%)), respectively. For colour scale ratings, intra-rater reliability (linear weighted kappa) ranged from 0.76 to 0.79, with the inter-rater reliability from 0.71 to 0.81. For the number of lesions, intrarater reliability ranged from 0.40 to 0.82 and inter-rater reliability from 0.24 to 0.67. Conclusions Intra-rater and inter-rater reliability were excellent for raw values and for ratios with deltoid muscle as the reference tissue, and good for ratios with gel pad as the reference tissue. The reliability of colour scale ratings was substantial-to-almost perfect, and for the number of lesions fair-to-almost perfect. Although high reliability was found, validity and responsiveness of these elastographic methods needs further investigation. Ethics approval The study protocol was approved by the Ethics Committee for the Region of South Denmark (S-20160115) and reported to the Danish Data Protection Agency (2014-41-3266).