Ultrasound shear wave elastography-derived tissue stiffness is positively correlated with rotator cuff tear size and muscular degeneration

Purpose The purpose of this study is to describe rotator cuff muscle stiffness in patients with different degrees of rotator cuff tear (RCT) severity and to assess its predictive ability for RCT reparability. Methods One hundred and thirty-three consecutive patients who were scheduled to undergo arthroscopic shoulder surgery were prospectively enrolled. Tendon retraction, fatty infiltration, and muscle atrophy were evaluated using magnetic resonance imaging. Shear modulus of supraspinatus (SSP) and infraspinatus (ISP) muscles were measured by ultrasound shear wave elastography (SWE). The tear size and reparability were determined intraoperatively. Results There were 97 patients in RCT group and 36 patients in control group. Bilateral shear modulus discrepancy (Δshear modulus) was used to represent rotator cuff stiffness. Severely fatty-infiltrated rotator cuff muscles possessed a significantly higher stiffness compared with their counterparts (SSP: CI 27.8–31.8 vs. 13.5–15.6 kPa, ISP: CI 33.2–38.1 vs. 8.8–11.2 kPa, p < 0.001). The same trend applied to muscles with distinct tendon retraction (SSP: CI 27.7–32.3 vs. 10.9–14.9 kPa, ISP: CI 33.2–38.6 vs. 6.5–11.0 kPa, p < 0.001) and obvious muscle atrophy (SSP: CI 27.9–32.1 vs. 13.6–15.8 kPa, ISP: CI 32.9–38.2 vs. 9.0–11.7 kPa, p < 0.001). Irreparable massive RCT (MRCT) patients had significantly stiffer SSP (CI 27.7–31.9 vs. 13.5–16.5 kPa, p < 0.001) and ISP (CI 33.5–37.8 vs. 10.3–14.8 kPa, p < 0.001) than reparable MRCT. The Δshear modulus of the ISP was a highly accurate predictor of RCT reparability. A cutoff value of 18.0 kPa had a sensitivity of 100% and specificity of 98.8% for irreparable MRCT. Conclusion Ultrasound SWE-derived rotator cuff muscle stiffness is closely correlated with RCT size and severity. Level of evidence I.