Measurement properties of shear wave elastography for evaluating rotator cuff muscle stiffness: a systematic review

Background: Literature assessing elasticity in rotator cuff (RC) muscles with shear wave elastography (SWE) is growing but little is known about the overall measurement properties. However, this information is crucial before implementation in research or practice. The objective of this review was first, to systematically investigate the evidence regarding reliability and validity of rotator cuff (RC) muscles shear wave elastography (SWE). Second, to summarize measurement protocols to support uniformity and standardization of SWE methodology.

Methods: A literature search was conducted using Medline (PubMed), Web of Science and Embase. Included studies reported measurement properties of reliability, validity and/or responsiveness of SWE to evaluate RC muscle stiffness in subjects without and with musculoskeletal shoulder pain. Methodological quality was rated with the Consensus-Based Standards for the Selection of Health Measurement Instruments checklist. The level of evidence was determined using a best-evidence synthesis approach.

Results: Forty-two articles were included. Studies assessing reliability (n=29) had a moderate level of evidence (LoE) for positive ratings of intratester reliability for Supraspinatus (SS), Infraspinatus (IS) and Teres minor (Tm) and intertester reliability for SS and IS. A limited LoE for positive ratings was implied for intertester reliability of Tm and unknown LoE for negative ratings for day-to-day variability of SS. Studies reporting on convergent validity (n=13) showed inconsistent correlation between SWE and other outcomes. Studies assessing discriminant validity (n=18) showed higher SWE in shoulder patients but not in frozen shoulder and RC tears. Studies reporting on responsiveness (n=10) showed decreased SWE values 1-2 months postop RC repair and after stretching.

Conclusion: Although RC muscle SWE measurements showed overall moderate reliability, few studies used appropriate reliability study designs and protocols. The evidence regarding convergent validity, discriminant validity, and responsiveness is inconsistent, underscoring the need to improve measurement procedures and explore day-to-day reliability. SWE is a potentially valuable technique for RC muscle assessment. However, future high quality methodological research with reliability and validity as a primary focus is needed to better understand its applicability in clinical practice.