Shear-wave elastography for measuring the stiffness of latent trigger points and surrounding areas in the infraspinatus muscle: intra- and inter-examiner reliability analysis.

Abstract

Objective: To explore the intra- and inter-examiner 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), inter-examiner reliability and mean differences in SWE and PPTs between MTrPs and control points DESIGN: Longitudinal observational study: Intra- and inter-examiner reliability study.

Setting: A University lab.

Participants: Forty participants with latent MTrPs within the infraspinatus muscle.

Interventions: None.

Main outcome measures: 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 inter-examiner reliability and SWE intra- and inter-examiner reliability. PPT and SWE scores were compared by location (MTrP and control) and gender (male/female).

Results: PPTs were significantly lower in MTrPs compared with control points in males (p=0.003) and females (p=0.006), and lower in females compared with males (MTrP p<0.001; control point p=0.001). Good inter-examiner reliability was found for PPTs (ICC>0.84) and SWE (ICC>0.82). Intra-examiner reliability for SWE was excellent (ICC>0.95) in both the novice and experienced examiners.

Conclusion: This study demonstrated excellent SWE intra-examiner reliability (ICCs>0.9) and good inter-examiner 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.