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

Abstract

INTRODUCTION\nThe 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.\n\n\nMATERIALS AND METHODS\nThis 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).\n\n\nRESULTS\nEight 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\u2009< 0.05). Group 1 had a postoperative improvement of 1° in their ER with elbow at side while group 2 had a 16.5° improvement (p\u2009=\u20090.002). Group 1 had a postoperative loss of 6.3° in their ER in 90° abduction while group 2 had a 21.7° improvement (p\u2009=\u20090.001). The SSV at the final assessment was 69% in group 1 versus 79% in group 2 (p\u2009=\u20090.094).\n\n\nCONCLUSION\nHaving a TM index of trophicity below 0.75 is a negative predictor of clinical outcomes due to lack of ER after RSA.\n\n\nLEVEL OF EVIDENCE\nIV.