9.2.1 Does Subscapularis Tendon Repair Contribute to Range of Motion after Reverse Shoulder Arthroplasty?

The subscapularis has important roles in the native shoulder and after RSA. Subscapularis function in the native shoulder provides internal rotation, adduction, and shoulder flexion in addition to contributing to concavity compression and anterior glenohumeral joint stability. ¹ However, there are significant changes in subscapularis function after RSA. Ackland et al showed that the subscapularis contributes to shoulder adduction, abduction, extension, and internal rotation ² after RSA with the Grammont design in a cadaveric biomechanical study. ¹ , ² Furthermore, the superior subregion of the subscapularis functions as an abductor, while the middle and inferior subregions function as adductors. ¹

9.2.2 Does Subscapularis Tendon Repair Contribute to Stability after Reverse Shoulder Arthroplasty?

Ackland et al concluded that the abduction–adductor cocontractions of the distinct subregions of the subscapularis after RSA generate a compressive force during abduction to potentially increase glenohumeral joint stability with the Grammont design. ¹ Edwards et al and Trappey et al demonstrated that patients with an irreparable subscapularis tendon demonstrated a higher rate of instability after RSA with a Grammont design. ³ , ⁴

Edwards et al reported on 138 consecutive reverse shoulder arthroplasties performed through a deltopectoral approach by a single surgeon with a minimum follow-up of 21 months and an average follow-up of 36 months. ³ All 7 dislocations in the series occurred in patients with an irreparable subscapularis tendon (7 dislocations out of 76 patients with an irreparable subscapularis tendon). There were no dislocations in the 62 patients with a repairable subscapularis tendon. In a follow-up study by Trappey et al, 284 reverse shoulder arthroplasties were evaluated with a minimum of 12-month follow-up and average of 24-month follow-up. Patients with an irreparable subscapularis tendon demonstrated a significantly higher rate of instability compared to patients with a repairable subscapularis tendon (p = 0.001). ³ Of 123 patients, 14 (12%) in the irreparable group had a dislocation compared to only 1 patient out of 161 patients in the repairable group (0.01%). ³

Gallo et al reported similar results with a consecutive series of 57 reverse shoulder arthroplasties consisting of 36 Grammont style implants and 21 implants with increased lateral offset. ⁵ Nine cases of instability occurred and all cases had an irreparable subscapularis. The authors concluded the lack of an intact and functioning subscapularis tendon likely contributes to instability. ⁵

A systematic review by Zumstein et al evaluated complications after RSA. ⁶ Instability was the most common postoperative complication (37 of 782 reverse shoulder arthroplasties, 4.7%) and the authors concluded that subscapularis tendon repair appeared to contribute to stability, and the subscapularis tendon should be repaired whenever possible. ⁶

A subsequent study was published by Clark et al, concluding that it may not be necessary to repair the subscapularis tendon to prevent instability after RSA using an implant with an increased lateral offset relative to the Grammont design. ⁷ This study retrospectively evaluated 120 reverse shoulder arthroplasties completed through a deltopectoral approach using an increased lateral offset designed implant and included patients with a minimum of 6 months of follow-up and an average of 13.2 months. There was no statistical difference between dislocations in the group with a subscapularis tendon repair (3 dislocations out of 55 reverse shoulder arthroplasties) and the group with a subscapularis tendon repair (2 dislocations out of 65 reverse shoulder arthroplasties). ⁷ A small series of 18 Grammont style implants reported by Boulahia et al demonstrated better postoperative active external rotation without subscapularis repair (p = 0.02). ⁸ However, Clark et al demonstrated in a much larger series that there were no statistical differences between the subscapularis tendon groups regarding gains in postoperative active forward flexion, external rotation, or internal rotation. ⁷