A low teres minor index of trophicity negatively impacts the functional outcomes of reverse shoulder arthroplasty

Introduction: The teres minor (TM) participates in active external rotation (ER) after reverse shoulder arthroplasty (RSA). The TM index of trophicity (T2/G) measured on CT scan is a predictor of poor results in patients who have irreparable rotator cuff tears. The aim of this study was to evaluate how T2/G impacts the functional outcomes of RSA in the context of massive rotator cuff tears. We hypothesized that a T2/G less than 0.75 is a predictor of worse functional outcomes.Materials and methods: This study involved 32 shoulders in 26 patients (mean age 71 years) who underwent RSA for cuff tear arthropathy and had a minimum follow-up of 1 year (mean 3 years). T2/G is the ratio between T2 (TM thickness) and G (maximum glenoid cavity thickness) on preoperative axial CT slices. Clinical examination at the final assessment involved determining the Constant score, the shoulder joint's range of motion and the Subjective Shoulder Value (SSV).Results: Eight shoulders had a T2/G of less than 0.75 (group 1) while 24 shoulders had an index above 0.75 (group 2). These two groups were similar preoperatively. The Constant-Murley score in group 1 was significantly lower than in group 2 (50.2 points versus 59.7 points, p < 0.05). Group 1 had a postoperative improvement of 1 degrees in their ER with elbow at side while group 2 had a 16.5 degrees improvement (p = 0.002). Group 1 had a postoperative loss of 6.3 degrees in their ER in 90 degrees abduction while group 2 had a 21.7 degrees improvement (p = 0.001). The SSV at the final assessment was 69% in group 1 versus 79% in group 2 (p = 0.094).Conclusion: Having a TM index of trophicity below 0.75 is a negative predictor of clinical outcomes due to lack of ER after RSA. Level of evidence: IV. (C) 2021 Published by Elsevier Masson SAS.