Reverse total shoulder replacement (RTSR) is a surgical procedure designed to address severe shoulder joint conditions, particularly when significant arthritis is present alongside a non-functional or severely damaged rotator cuff. Unlike traditional shoulder replacements that maintain the natural ball-and-socket configuration, RTSR reverses this setup, placing the ball on the shoulder blade and the socket on the upper arm bone. This altered design allows the deltoid muscle to assume a more prominent role in shoulder movement, compensating for the compromised rotator cuff.
Understanding Key Shoulder Muscles
The deltoid muscle, a large, triangular muscle, covers the top of the shoulder and is responsible for lifting the arm to the front, side, and back. It plays a role in arm abduction, moving the arm away from the body, and helps stabilize the shoulder joint.
Beneath the deltoid lies the rotator cuff, a group of four muscles and their tendons: the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles collectively stabilize the head of the upper arm bone (humerus) within the shoulder blade’s socket (glenoid). The supraspinatus initiates arm abduction, the infraspinatus and teres minor primarily facilitate external rotation, and the subscapularis is responsible for internal rotation of the arm.
The pectoralis major, a large, fan-shaped muscle located in the chest, also contributes to shoulder movement. It assists in movements such as bringing the arm across the chest (horizontal adduction) and internal rotation of the shoulder. This muscle, along with the deltoid and rotator cuff, works in concert to provide the shoulder’s broad functional capabilities in a healthy state.
Surgical Approach: Accessing the Joint
Surgeons commonly use a technique called the deltopectoral approach to access the shoulder joint during a reverse total shoulder replacement. This approach involves making an incision, typically 10 to 15 centimeters long, from near the coracoid process (a bony projection on the shoulder blade) down towards the arm. The incision follows the natural groove between the deltoid and pectoralis major muscles.
During this approach, the surgeon carefully identifies the deltopectoral groove, often marked by the cephalic vein. Instead of cutting through the deltoid or pectoralis major muscles, these muscles are separated and gently retracted. The deltoid is pulled laterally (to the side), and the pectoralis major is pulled medially (towards the center of the chest), creating a clear pathway to the shoulder joint without incising these major muscle bellies.
This careful separation minimizes trauma to these significant muscles, which is important for postoperative recovery and function. Minor tissues or ligaments, such as parts of the joint capsule, might be released to improve visualization of the joint and facilitate proper implant placement. The deltopectoral approach is favored for its ability to provide good exposure to the front of the shoulder and the glenohumeral joint while preserving the integrity of major muscle groups.
Muscles Affected and Preserved During Reverse Total Shoulder Replacement
The surgical strategy for a reverse total shoulder replacement significantly differs from traditional shoulder replacements, particularly regarding how muscles are managed. The deltoid muscle is carefully preserved throughout the procedure; it is retracted laterally to allow access to the joint but is not cut. This preservation is critical because, after RTSR, the deltoid becomes the main muscle responsible for lifting and moving the arm, compensating for the often non-functional rotator cuff.
The rotator cuff muscles—supraspinatus, infraspinatus, teres minor, and subscapularis—are typically already compromised in patients undergoing RTSR, which is often the underlying reason for the surgery. Unlike some other shoulder procedures, the existing state of these muscles, rather than their surgical incision, is the focus. While the subscapularis tendon may sometimes be released for exposure, its management in RTSR is a topic of ongoing discussion among surgeons. Some approaches attempt to preserve or repair the subscapularis if its quality allows, as it contributes to internal rotation and joint stability. However, some studies suggest that subscapularis repair may not significantly improve outcomes in RTSR, especially with certain implant designs.
The other rotator cuff muscles (supraspinatus, infraspinatus, teres minor) are generally not cut for surgical access in RTSR, as their pre-existing deficiency is the condition being treated. Instead, the surgery reconfigures the joint mechanics to rely on the deltoid muscle. Any other releases are typically limited to smaller soft tissues or portions of the joint capsule to ensure adequate exposure and proper seating of the prosthetic components, rather than major muscle groups. The overall approach emphasizes retraction and preservation of the deltoid, acknowledging the pre-existing state of the rotator cuff, to optimize post-operative shoulder function.