41.1.1 Restoration of Subscapularis

Surgical exposure to the glenohumeral (GH) joint in total shoulder replacement (TSR) requires takedown of the subscapularis tendon at its insertion, which can be performed using various techniques, which include tenotomy, tendon peel, and lesser tuberosity osteotomy (LTO). Preoperative planning of the exposure is important so that the subscapularis tendon can be addressed appropriately at the end of the case. Adequate mobilization of the tendon is also important, as preoperative internal rotation contractures are common in GH osteoarthritis. The purpose of repair is to restore subscapularis function, thereby providing stability and motion to the shoulder postoperatively.

41.2.1 Stability

The subscapularis tendon resists anterior translation of the humeral head relative to the glenoid. An intact tendon reduces the risk of postoperative anterior instability. It also creates a concentric joint and distributes polyethylene contact surface area. Several studies have demonstrated increased risk of anterior instability after both conventional and reverse TSR in patients without an intact subscapularis tendon. ^{1 – 5} Some recent data suggest that an intact subscapularis may not be necessary after reverse TSR and does not result in increased instability rates. ⁶

41.2.2 Motion

Repair of the subscapularis tendon theoretically restores the subscapularis’s main function of internal rotation. This is particularly important to patients as it allows for reaching into the back pocket and tucking in a shirt. The subscapularis also draws the humeral head forward and downward when the arm is raised. By providing a stable and balanced joint, a restored subscapularis improves the function of the deltoid and other rotator cuff muscles.

41.2.3 Improved Outcomes

Patients with an intact subscapularis after TSR, compared to those without an intact or functioning muscle, report improved Disabilities of the Arm, Shoulder, and Hand (DASH) scores ⁷ and patient-reported outcomes. ^{2 , 8 , 9} Subscapularis tendon management in TSR yields similar overall patient outcome scores, and no specific technique is considered superior. ¹⁰ Several studies report excellent or satisfactory outcome after subscapularis tenotomy and repair. ^{11 – 14} Caplan et al reported normal belly press at final follow-up after tendon-to-tendon repair, ¹⁵ though Miller et al report 65% altered subscapularis function with this technique. ⁹

LTO provides anatomic repair of the lesser tuberosity footprint and reliable bone-to-bone healing. ⁵ Initial fixation of LTO is stronger ^{16 – 18} ; however, biomechanical studies demonstrate similar long-term outcomes between each repair technique. ^{10 , 16 – 20}

41.3.1 Challenges with Mobilization

Complete mobilization of the subscapularis is important in the exposure of the glenoid as well as the ability to repair the tendon upon completion of the TSR. Preoperative contractures as well as implant lateralization can make it difficult to obtain an anatomic subscapularis repair. This can be problematic in LTO repairs. Tenotomies and peel techniques can be medialized to the anterior humeral neck osteotomy if needed.

41.3.2 Subscapularis and Reverse Total Shoulder Replacement

Subscapularis repair may not always be advantageous after reverse TSR. A recent biomechanical study reported that concomitant subscapularis repair with reverse shoulder arthroplasty (RSA) created a biomechanically unfavorable condition during arm elevation, due to an increase in the force required by the deltoid and posterior rotator cuff. ²¹ They also found significantly increased joint reaction forces when the subscapularis was repaired. ²¹ Giles et al confirmed these findings in another cadaveric study and concluded that rotator cuff repair, especially in conjunction with glenosphere lateralization, produced an antagonistic effect that increased deltoid and joint loading. ²²