Does the Teres Minor Muscle Status Affect the Active Rotation Movement In Reverse Total Shoulder Arthroplasty?

Abstract

To assess the correlation between teres minor (TM) integrity and fatty infiltration and postoperative active external rotation (AER) in patients operated with reverse total shoulder arthroplasty (rTSA) rTSA provide good active elevation, however, there are concerns regarding deficient or absent active external rotation. The Teres Minor degeneration and fatty infiltration has been implicated. Between 2005 - 2015, 109 shoulders in 97 patients (mean age 75.7±8.9; 31 M, 66 F) underwent a primary metaphyseal rTSA for painful cuff tear arthropathy or massive irreparable rotator cuff tear with glenohumeral joint degeneration. Patients were prospectively clinically assessed preoperatively, at 3weeks, 3, 6, 12 months and yearly postoperatively: Constant Score (CS), Subjective Shoulder Value (SSV), Patient Satisfaction Score (PSS) were used. TM fatty infiltration was evaluated according to Goutallier classification, while TM muscular degeneration according to Walch morphological classification. Consequently, all the shoulders were divided in 2 groups respectively: group A, Goutallier grade 0-1-2; group B, Goutallier grade 3-4 and group A1, Walch hypertrophic/normal and group B1, Walch atrophic/absent The CS, SSV and AER improved significantly at 12-month follow-up assessment in all the patients (p <0.001). However, CS, AER and SSV have not shown statistically significant differences when comparing the different subgroups (A/B and A1/B1). Mean AER improved from 22.4°±21.6° preoperatively to 40.6°±17.5° postoperatively (+18.1°±21.5°) in all the subgroups. It seems that TM degeneration does not affect AER in patients that underwent rTSA for cuff tear arthropathy. It may relate to specific design concepts of the implant used or to the surgical technique used. Additional clinical and biomechanical studies are necessary to understand the reasons that have led to these results.