The shoulder is one impressive joint. It has a range of motion greater than any other joint in the entire body.

Except when things go wrong. Age, injury, arthritis - they all can spell problems that begin with pain and end with a patient not even being able to lift an arm above the shoulder.

Although the number of shoulder replacements nationwide falls far behind those of hip and knee replacements, about 53,000 people a year get them, according to the Agency for Healthcare Research and Quality.

Enter Gerald R. Williams Jr., a Philadelphia surgeon who for a quarter of a century has focused his career largely on shoulder replacements. He is the John M. Fenlin Jr. Professor of Shoulder and Elbow Surgery at the Rothman Institute and the Sidney Kimmel Medical College at Thomas Jefferson University.

Recently, Williams was named president of the American Academy of Orthopaedic Surgeons. One of the many things he aims to do is to draw attention to what he contends is an overuse of a particular kind of surgery - a reverse shoulder replacement.

What is a reverse shoulder replacement? How is it different from a regular one?
The shoulder is a ball-and-socket joint. In a regular joint, the socket is on your shoulder blade, and the ball is on the top of your arm. So in a regular replacement, you put in a new metal ball on top of the arm, and you resurface the socket with plastic.

In the reverse shoulder replacement, you put a new metal ball where the socket used to be, and on the top of the arm, instead of a ball, you put a plastic socket. So the pieces are reversed.

What does that achieve?
It is intended for patients who have rotator cuff problems, in addition to being arthritic.

In a regular shoulder, when you go to raise your arm, the rotator cuff muscles are what hold the ball against the socket and allow it to rotate. Imagine that you are standing on a very slick marble floor and there is a ladder lying next to you, and somebody says they want you to raise the ladder. You would pick up one end and raise it to a point, but then the other end would keep sliding away from you. Unless you had a friend that stood at the other end of the ladder and put their foot on it so you could just rotate the ladder up. The ladder is your arm. Where the ladder meets the floor is the shoulder joint. And your friend's foot is the rotator cuff.

But the rotator cuff can tear, from aging, from trauma and simple wear and tear, but mostly it's aging. In a shoulder that has a bad rotator cuff tear, it's the same as having nobody to put their foot at the top of the ladder. So the ball slides instead of rotates.

Because of the way it is designed, a reverse shoulder replacement prevents the unnatural sliding that occurs in the absence of a good rotator cuff and allows an entirely different muscle - the deltoid muscle, the muscle that gives men their wide shoulders - to create pure rotation that raises the arm.

For years, we had many patients that had large rotator cuff tears, plus arthritic shoulders, and couldn't raise their arms. But we had no solution for them. For some patients, their dominant arm was worthless. They couldn't do anything but scratch their nose. But once the procedure was approved by the U.S. Food and Drug Administration in 2004, you could put in a reverse ball and socket, and not only did it remove their pain. It also made it so they could raise their arm again. You can imagine what it would be like.

So far, all this sounds great. What happened next?
I personally think it is being used too often now. The pendulum has swung in the other direction. At first, we really only used reverse shoulder replacements in elderly patients that were sedentary. What's happened over the years is that it's worked a lot better in more situations than we thought, and as a result, the uses have expanded.

We did a study about a year ago and found that, among Medicare patients in the U.S., there are almost as many reverse shoulder replacements as regular ones. There are places in the U.S. where surgeons do more reverse shoulder replacements than all other anatomic replacements combined. I don't know that it says for sure there's overutilization, but it certainly raises the question.

Why would that be a problem?
The complication rate for reverse shoulder replacements is higher than in regular ones. The infection rate and the dislocation rate are higher. And, what we also found in our study, the cost of a reverse shoulder replacement is dramatically higher, sometimes double.

But average hospital reimbursement from Medicare is about the same for both procedures. At present, surgeons are able to do what they think is best for their patients, regardless of cost. In the new value-based system, however, the cost or utilization will likely have to come down.

What's your advice to patients?
I get patients coming in every day demanding a reverse shoulder replacement, just because they've heard about them or read about them. They have no idea what's wrong with them. The right patients will do extremely well and will be very happy with a reverse shoulder replacement. But it's not for everybody, and you should trust your doctor to know what's right for you.