The reverse shoulder replacement is a shoulder implant that has been used successfully for over ten years in Europe. It was approved by the FDA for use in the United States in 2004. It specifically designed for use in shoulders that have a deficient rotator cuff and severe arthritis. In addition, it can be used in the setting of complex fractures and failure of previous shoulder replacements in which the rotator cuff has become deficient deficient.
The normal shoulder is a ball and socket joint (Figure 1). The ball is called the humeral head and the socket is called the glenoid. The rotator cuff is a series of four muscles that hold the shoulder in the socket and help the shoulder move. When torn, the rotator cuff is usually repaired surgically. In some cases, surgical repair of the rotator cuff is not possible. Over the course of many years, the shoulder can develop a unique type of arthritis due to massive rotator cuff tearing. This end stage of a massively torn, irreparable rotator cuff tear is called cuff tear arthropathy of the shoulder, a difficult to treat combination of arthritis and a massive rotator cuff tear.
A normal shoulder has cartilage on the ball and socket to enable smooth gliding motion (Figure 2). In the arthritic shoulder the normal cartilage is worn away instead of cartilage gliding smoothly on cartilage, bone rubs roughly against bone, creating pain and inflammation. On x-ray, the joint space narrows and osteophytes (bone spurs) form (Figure 3). When the rotator cuff is intact, a conventional shoulder replacement replaces the ball and socket joint with metal and plastic, eliminating pain and restoring range of motion (Figure 4).
Figure 4. These three x-rays represent a conventional shoulder replacement that is used when the rotator cuff is intact. Conventional shoulder replacement uses a press fit humeral stem and a cemented three pegged polyethylene glenoid component to resurface the shoulder joint and eliminate pain.
When an irreparable rotator cuff tear of large size goes untreated for many years, a condition called cuff tear arthropathy gradually develops. The humeral head loses its containment within the rotator cuff and begins to articulate with the acromion. On x-ray, this manifests as not only arthritis between the ball and socket joint (Figure 5). Cartilage wear ensues. In the most severe cases, the patient has intractable pain and is unable to raise the arm. Conventional shoulder replacement with a hemiarthroplasty (half of a shoulder replacement) is unpredictable for pain relief and gain of function. The reverse prosthesis was designed to improve upon the results of conventional shoulder replacement in the setting of a deficient rotator cuff.
Figure 5. The Hamada classification of rotator cuff tear arthropathy shows progressive stages of arthritis of both glenohumeral and acromiohumeral spaces.
The reverse shoulder replacement (Figure 6) changes the orientation of the shoulder so that the normal socket (glenoid) is replaced with a metal ball, and the normal ball (humeral head) is replaced with a humeral stem with a socket. The humeral socket then rests under the glenoid ball. The mechanics of the shoulder are changed in such a way that the deltoid muscle now has tension, restoring the patient's ability to raise the arm and improving the pain from arthritis.
Figure 6. A reverse shoulder replacement consists of a humeral stem with a concave socket attached that articulates with a hemispherical glenoid componenent (glenosphere) in a semiconstrained fashion. This metal on plastic articulation improves pain and range of motion by changing the anatomy of the shoulder to restore deltoid tension.
Figure 5A: A typical patient with rotator cuff tear arthropathy has a high riding humeral head with arthritis between glenoid and humerus as well as arthritis between acromion and humerus.
Figure 5B: After reverse total shoulder replacement, the acromiohumeral interval and deltoid tension have been restored.
Figure 5C+D: Preoperative x-rays of severe rotator cuff tear arthropathy
Figure 5E: After treatment with reverse total shoulder replacement
Some shoulder fractures are complex and involve the part of the bone where the rotator cuff tendons insert. The goal of the shoulder surgeon in the setting of shoulder fracture surgery is to enable the fracture to heal with a functioning rotator cuff.
Displaced shoulder fractures in this setting are usually treated with either a plate and screws or a hemiarthroplasty (shoulder replacement of the humerus alone). When these fractures fail to heal or when the rotator cuff fails to heal to the prosthesis, pain and inability to lift the arm ensues. The reverse prosthesis is a salvage operation for the painful, failed shoulder fracture.
Lastly, previous shoulder replacements can become rotator cuff deficient over time and can also be salvaged with a reverse prosthesis.
In the setting of previous fracture surgery and/or a previous prosthesis, the complication rate is much higher than in cuff tear arthopathy alone. Figure 6 shows conversion of a failed, dislocated hemiarthroplasty using a reverse total shoulder replacement.
Figure 6A+B: Preoperative x-rays of a failed hemiarthroplasty dislocated superiorly. This painful shoulder was treated with a reverse total shoulder replacement (6C).
The complication rate for the reverse prosthesis is about 10% in primary surgery (no previous surgery). The complication rate is 30-40% when revising previous surgery in the aforementioned salvage setting. For this reason, the problem being treated with a reverse prosthesis must be significant enough to warrant the high surgical risk. (e.g. daily, debilitating pain and inability to lift the arm). Complications include:
The reverse shoulder replacement is for severe pain and inability to lift the arm that affects daily life. Prior to undergoing a reverse replacement, you should have tried physical therapy, injections, medications, activity modification and watchful waiting, all without improvement. Risks are higher for this joint replacement than for conventional joint replacements, but the results can be excellent in the properly selected patient with a debilitating shoulder condition.