Shear Wave Elastography for Measuring the Stiffness of Latent Trigger Points and Surrounding Areas in the Infraspinatus Muscle: Intra- and Interexaminer Reliability Analysis.

Abstract

To explore the intra- and interexaminer reliability of shear wave elastograhy (SWE), (an objective alternative to highly subjective procedures with poor inter-rater reliability such as manual palpation) in measuring the stiffness of latent myofascial trigger points (MTrPs) and healthy surrounding areas in the infraspinatus muscle, pressure pain threshold (PPT), interexaminer reliability, and mean differences in SWE and PPTs between MTrPs and control points. Longitudinal observational study: Intra- and interexaminer reliability study. A university laboratory. Forty participants (N=40) with latent MTrPs within the infraspinatus muscle. Not applicable. One experienced examiner identified and classified latent MTrPs and selected an asymptomatic control point within the infraspinatus muscle. Later, 2 blinded examiners assessed once the PPTs (blinded to the scores) and acquired 2 SWE images of each location. Reliability estimates were calculated for assessing PPT interexaminer reliability and SWE intra- and interexaminer reliability. PPT and SWE scores were compared by location (MTrP and control) and gender (male/female). PPTs were significantly lower in MTrPs than control points in males (P=.003) and females (P=.006), and lower in females than males (MTrP P<.001; control point P=.001). Good interexaminer reliability was found for PPTs (intraclass correlation coefficient [ICC]>0.84) and SWE (ICC>0.82). Intraexaminer reliability for SWE was excellent (ICC>0.95) in both the novice and experienced examiners. This study demonstrated excellent SWE intraexaminer reliability (ICCs>0.9) and good interexaminer reliability (ICCs>0.82). Although PPT scores indicated significant differences in hyperirritability between latent MTrPs and control points, SWE measurements revealed no significant differences in muscle stiffness.