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

Reverse total shoulder arthroplasty (rTSA) provide good active elevation, however, there are concerns regarding deficient or absent active external rotation (AER). Teres Minor (TM) degeneration and fatty infiltration has be implicated. This study assesses the correlation between TM integrity and fatty infiltration and postoperative AER in patients operated with rTSA.

Between 2005 and 2015, 109 shoulders in 97 patients (mean age 75.7±8.9; 31M, 66F) underwent a primary short 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 (Table).

Goutallier and Walch classification subgroups

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°) with no statistically significant difference (p = 0.43 A/B; p = 0.85 A1/B1).

It seems that TM degeneration does not affect AER in patients who underwent rTSA for cuff tear arthropathy with the specific design of rTSA implant. It may, however, relate to specific design concepts of the implant used. Additional clinical and biomechanical studies are necessary to understand the reasons that have led to these results.