Reverse shoulder replacement is a better type of shoulder replacement when the rotator cuff is dysfunctional, or is expected to be dysfunctional.
In a regular shoulder replacement (TSA) the head of the humerus is replaced with a metallic head, and the cartilage of the glenoid is replaced with a layer of plastic.
In a reverse shoulder replacement the locations of the ball and socket are reversed: the glenoid socket is replaced with a metal sphere, the humeral head is fitted with a plastic socket.
Like a regular shoulder replacement, a reverse shoulder replacement is performed by using power saws, reamers, chisels, etc., to remove bone from both sides of the glenohumeral joint. The removed bone is then replaced with artificial materials.
When the rotator cuff cannot be counted on to keep the head of the humerus on the glenoid, a regular shoulder replacement will result in instability, subacromial impingement, and continued inability to raise the arm.
A reverse shoulder replacement adresses the problem by providing a mechanical barrier to the proximal migration of the humerus: The artificial "ball" on the glenoid serves as the joint pivot which allows the deltoid muscle to elevate the arm. A reverse shoulder replacement therefore allows better motion in cases of rotator cuff arthropathy or in certain cases of comminuted proximal humerus fractures.
In the setting of severe glenohumeral arthritis with weak or torn rotator cuff tendons, a regular shoulder replacement will fail to provide adequate pain relief.
In cases of comminuted proximal humerus fractures, osteosynthesis with plate and screws has a higher likelihood of failure, and hemiarthroplasty (partial replacement) has been the historical alternative treatment. The problem with hemiarthroplasty in fracture cases is this: the rotator cuff tendon often does not heal to the artificial prosthesis. Therefore, in recent years *reverse replacement** has become the solution to this problem, albeit not a perfect solution.
Here is a list of risks of reverse shoulder replacement:
Reverse shoulder replacement is no longer an experimental procedure, but it does not have the track record of, say, hip replacement or knee replacement prostheses. It is an operation that is best reserved for elderly patients, or for extreme cases.
The xrays below are from a patient with left sided rotator cuff arthropathy. Patient presented with chronic shoulder pain and difficulty raising arm.
On the left is the pre-surgery appearance of the left shoulder. Note the new distal location of the humerus compared to the situtation before surgery.
This patient initially elected to not have surgery. Approximately 3 weeks later she reevaluated her situation and sought surgical treatment due to continued severe pain. The reverse shoulder replacement was done over 1 month after the injury.
Reverse shoulder replacement resulted in quick improvement.
Range of motion after reverse replacement is expected to be less than the full natural range of motion of the shoulder joint. This patient was able to raise the arm above the shoulder level. She became able to wash her face, comb her hair, and feed herself within 1 month. She was able to drive 6 weeks after surgery.
This is the xray appearance approximately 2 years later.