Reverse shoulder replacement (RSA) is a specialized surgical procedure primarily for patients with shoulder arthritis and an irreparable rotator cuff tear. It is also commonly used following a previous failed shoulder replacement. The main goals of RSA are to provide significant pain relief and restore functional movement, prioritizing the ability to lift the arm. This design sacrifices a full, natural range of motion in favor of stability and function, which is a necessary trade-off when the body’s primary stabilizers are damaged.
Understanding Reverse Shoulder Mechanics
The fundamental difference in a reverse shoulder replacement lies in the joint’s anatomy. In a healthy shoulder, the ball (humeral head) is on the arm bone and the socket (glenoid) is on the shoulder blade. The RSA procedure reverses this arrangement, attaching the ball component to the shoulder blade and the socket component to the arm bone. This shift changes the joint’s center of rotation, altering the mechanical relationship of the surrounding muscles.
This new configuration converts the large deltoid muscle into the primary functional elevator of the arm, taking over the role of the damaged rotator cuff. The increased mechanical advantage allows the deltoid to lift the arm despite the absence of a functioning rotator cuff. Overall shoulder function is inherently different and more constrained than a healthy joint because the deltoid manages movement previously handled by the rotator cuff.
Specific Targets for Range of Motion
The expected range of motion (ROM) after RSA is specific to the procedure. A successful outcome means achieving functional movement, particularly forward and outward. Patients generally achieve active forward elevation, or lifting the arm straight out, in the range of 90 to 120 degrees. While some patients reach up to 140 degrees, anything beyond 90 degrees is considered a good result for daily tasks.
Lifting the arm out to the side (abduction) is often limited to approximately 90 degrees post-surgery. These elevation and abduction ranges are sufficient for reaching head height and performing most activities of daily living. Rotational movements show the most significant limitations, especially external rotation (twisting the arm outward). Active external rotation is frequently restricted, typically ranging from 0 to 20 degrees, sometimes up to 30 degrees.
Internal rotation, or reaching behind the back, is also functionally limited, making tasks like tucking in a shirt difficult. The goal for internal rotation is usually to allow the hand to reach the lower back or beltline. These rotational limitations result directly from the implant design and surgical approach, which prioritize stability and deltoid function over a full, natural range of motion.
The Rehabilitation Timeline
Achieving functional range of motion targets follows a structured rehabilitation timeline. The initial phase, lasting the first six weeks, focuses on joint protection and allowing soft tissues to heal. The arm is kept in a sling, and patients only perform passive range of motion (PROM) exercises, where the arm is moved by a therapist or the other hand. Patients must strictly avoid active lifting or pushing with the surgical arm, which could jeopardize tissue healing.
The next phase, typically from week six to twelve, transitions to active-assisted and then active range of motion (AROM) exercises. This is when the deltoid muscle begins to take on its new primary function. Physical therapy focuses on gradually strengthening this muscle without overexerting it, and light strengthening exercises are introduced toward the end of this period.
From three to six months post-operation, the focus shifts entirely to active strengthening and endurance. Most patients achieve their functional range of motion and return to most daily activities by the six-month mark. Continued improvement in strength and function can occur for up to a year or longer, with the final phase involving a home exercise program designed to maintain gains.
Long-Term Functional Restrictions
Patients must adhere to certain permanent restrictions to protect the longevity of the implant. The most significant restriction involves lifting heavy objects, especially overhead. Patients are advised to avoid lifting anything heavier than 10 to 15 pounds with the operative arm, though some sources allow up to 20 to 25 pounds.
Repetitive, high-impact, or forceful movements should also be avoided indefinitely to prevent excessive wear on the artificial joint. Activities such as contact sports, heavy gardening, or using the arm to push off a chair to stand up are generally discouraged. Avoiding extreme rotational movements, particularly forced external rotation, is a long-term precaution to maintain joint stability and prevent potential dislocation. These guidelines are necessary because the unique mechanics of the RSA make the joint susceptible to complications from high forces.