Assessing the supraspinatus-to-trapezius cross-sectional thickness ratio as a quantitative classification for rotator cuff injury

Objectives: Rotator cuff injuries are a common musculoskeletal pathology, disrupting the function of the shoulder and restricting patients’ daily activities. The severity of muscle injury is determined through Goutallier grading, measured by the degree of fatty infiltration as calculated through magnetic resonance imaging (MRI). Furthermore, Goutallier grading is not fully quantitative as the level of fatty infiltrates relies on professional observation. This paper aims to assess whether the supraspinatus: Trapezius thickness ratio measured on MRI correlates with Goutallier grading, with the long-term goal of developing an ultrasound-based surrogate for clinical use. Materials and Methods: This retrospective cross-sectional observational study measured the supraspinatus-to-trapezius (SS:TRAP) cross-sectional thickness in 150 patients on MRI scan. The maximum thickness of the supraspinatus and trapezius muscles was calculated at the level of the spinoglenoid notch. The Goutallier grade was independently assessed by two fellowship-trained musculoskeletal radiologists with 1 year and over 10 years of experience, respectively. A one-way analysis of variance (ANOVA) test was used to assess the mean differences between the supraspinatus: Trapezius ratio, and P < 0.05 was considered significant. Results: The mean SS:TRAP ratio for each Goutallier grade was also calculated on the MRI at 2.46, 2.09, 1.25, 1.19, and 0.92, respectively. A one-way ANOVA test was used to assess the variability in mean ratios. This generated an F ratio = 18.74 ( P < 0.00001), showing there is a statistically significant difference between the mean ratios. Conclusion: There is a significant correlation between the supraspinatus: Trapezius thickness ratio, highlighting its potential use as a diagnostic classification tool.