A Randomized Control Trial to Evaluate Release Versus Non-release of Pectoralis Minor With Reverse Shoulder Arthroplasty

Shoulder arthroplasty has been increasing at exponential rates, particularly due to the rise of reverse shoulder arthroplasty (RSA). Postoperative complications after RSA include infection, instability, hardware component loosening, acromial and scapular spine fractures, neurologic injury, and scapular notching which can all cause pain. However, despite excluding these causes, some patients can have persistent anterior shoulder pain with poor motion.

RSA prostheses work by translating the center of rotation (COR) inferiorly and medially, which increases tension on the deltoid, which is thought to increase the deltoid's mechanical moment arm and thus its ability to abduct and flex the humerus. However, excessive lengthening may be a cause of acromial and scapular spine fractures or neurologic injury. In addition, other structures are tensioned, including the conjoint tendon (short head of the biceps brachii and coracobrachialis) and pec minor (PM). It is unclear if lengthening these muscle-tendon units has functional consequences or whether it can create an intrinsic pathology. It is therefore feasible that muscle lengthening could create tendinitis, which could lead to persistent anterior shoulder pain after RSA. In addition, excessive tension or over-activity in the PM is also known to be a cause of altered scapula biomechanics.

Good scapula biomechanics after RSA are critical to preserving an impingement-free range of motion, which is important in maximizing postoperative outcomes, implant longevity, and preventing component loosening and instability. However, it is known from the non-arthroplasty population that during repetitive movements with scapular protraction, a hyperactive or spasming PM shortens and develops contracture, leading to protracted resting scapular position and altered scapular contribution to shoulder range of motion.1 This causes altered scapular kinematics, or dyskinesia, and alters scapular accommodation to shoulder motion, a well-known feature in various shoulder pathologies. This can be a major problem after RSA when scapula accommodation is critical to ROM and function.

Due to the expendability of the pectoralis minor, its release would cause minimal functional detriment in non-pathological cases, but in cases of overactivity, release could markedly improve scapula biomechanics. This can be performed open or arthroscopically, but the concomitant open release would be straight-forward at the time of the index surgery through the same incision