Reverse shoulder replacement

Overview

Shoulder joint anatomy showing the humeral head, glenoid socket, and rotator cuff muscles (supraspinatus and infraspinatus). — **Shoulder anatomy.** The shoulder is a shallow ball-and-socket joint. The top of the upper-arm bone (humerus) sits against a small dish on the shoulder blade (glenoid), and four rotator-cuff tendons wrap around the ball to hold it centered during every arm motion.

When the rotator cuff is irreparable, an anatomic shoulder replacement will not work — the ball will not stay centered in the socket without the cuff. The reverse design solves that biomechanical problem by swapping the articulation: the ball is fixed to the glenoid and the socket to the humerus. This moves the center of rotation medially and downward, giving the deltoid the leverage to lift the arm even when the cuff cannot.

How the Procedure Works

Three AP shoulder radiographs showing different designs of reverse total shoulder arthroplasty, each with a glenosphere bolted to the shoulder blade and a polyethylene cup seated on the humeral stem. — **Post-op reverse shoulder replacement.** The ball-and-socket is reversed — the ball is fixed to the shoulder blade and the socket sits on top of the arm bone. This lets the deltoid lift the arm when the rotator cuff is too damaged to work.

The critical step on the glenoid side is baseplate fixation: the central peg or screw must engage the strongest bone at the glenoid vault, and peripheral screws are directed to maximize pull-out strength — a loose baseplate is the most consequential failure mode in this operation. The glenosphere is then locked onto the baseplate. On the humeral side, we choose stem length and offset, then set the polyethylene socket height to tension the deltoid: too little tension and the joint dislocates, too much and the patient loses comfortable motion and risks scapular notching. We check range of motion and stability with trial components before committing to final implants. The remaining deltoid does all the work from this point forward — the implant geometry provides the lever arm the cuff can no longer provide.

When to Consider Reverse Shoulder Replacement

Reverse shoulder replacement is generally offered when symptoms, imaging, and a trial of non-operative care together point to surgery as the next step. The typical picture includes:

Rotator cuff arthropathy
Long-standing rotator cuff deficiency leading to cuff tear arthropathy — arthritis in a cuff-deficient shoulder.
Massive irreparable cuff tear
A huge cuff tear with pseudoparalysis — the inability to actively elevate the arm.
Failed prior shoulder replacement
Revision from a failed anatomic replacement or fracture hemiarthroplasty.