Supraspinatus Fatty Infiltration Correlation with Handgrip Strength, Shoulder Strength, and Validated Patient-Reported Outcome Measures in Patients with Rotator Cuff Tears.

Introduction: The purpose of this study was to investigate the relationships between supraspinatus atrophy on magnetic resonance imaging (MRI) and other objective parameters in patients with rotator cuff tears. It was hypothesized that high-grade supraspinatus fatty infiltration would be correlated negatively with handgrip strength, shoulder strength, and patient-reported outcome measures (PROMs). Methods: Patients with MRI-proven rotator cuff tears treated by a single sports medicine fellowship-trained orthopaedist at a single institution underwent comprehensive preoperative evaluation including bilateral handgrip and shoulder strength measurements with dynamometers and multiple online questionnaires from the Surgical Outcomes SystemTM (Arthrex, Naples, FL). Available shoulder MRIs were reviewed to grade supraspinatus fatty infiltration severity according to the 5-tier Goutallier system and an alternate 3-tier classification scheme. Difference analysis and Spearman (rho) rank order correlation were applied to the collected data to define the relationships between supraspinatus fatty infiltration and key variables including handgrip strength, shoulder strength, and scores derived from the shoulder PROMs. Results: Ninety of the 121 patients enrolled in the study had shoulder MRIs available for review. There was no correlation found between supraspinatus fatty infiltration and handgrip strength, shoulder abduction strength, or any of the seven common shoulder PROM scores evaluated. There was statistically significant, albeit weak, correlation between MRI-derived fatty infiltration and shoulder external rotation strength. Conclusions: Contrary to the hypothesis, high-grade supraspinatus fatty infiltration is largely unrelated to and should not be considered predictive of handgrip strength, shoulder strength, or common shoulder PROM scores.