Anatomic vs. Reverse Shoulder Replacement: Which One Is Right for You?

I'm Patrick Denard from the Oregon Shoulder Institute. I'm a shoulder surgeon. I've been in practice for over 10 years and I do 100% shoulder in my practice. One of the most common questions I get when I do a shoulder replacement is, what is the difference between an anatomic and a reverse shoulder replacement? So I want to do a little bit of a deeper dive into the history, kind of usage, indications, and outcomes after these two different types of replacements. So an anatomic shoulder replacement, just foundationally, what is done is a plastic component most commonly is placed in the socket or the glenoid. This is a high-strength plastic made of polyethylene. And on the other side, the humeral side, a metal ball is placed. Now for years, what has been done is a stemmed implant has been done where a stem is put inside of the humeral bone. But in more recent years, this has transitioned to short stems and now a stemless component And the advantage here is really more bone preservation, uh, that leads to less invasiveness. It's been shown that actually sleep is better after this compared to a standard replacement and pain is lower. And then also it's easier to revise if that would ever be necessary. But with an anatomic replacement, regardless whether there's a stem or not, what you're trying to do is restore the anatomy, trying to match the anatomy as best as possible. You see the most of the bone just stays the same, but you're replacing the joint and you're trying to do that to match the anatomy. And now the shoulder is an inherently unstable joint. It's kind of like a ball on a golf tee, I'll tell people, because it can glide very, very easily. So what holds the shoulder in place is the rotator cuff. So the rotator cuff comes over this joint. There's 4 rotator cuff muscles that surround the ball and socket joint and provide stability. To keep that ball in place. Now, when the rotator cuff is not functioning effectively, or there are other causes for instability, if you place a metal ball, it's going to move around inappropriately. That will lead to toggle on this plastic piece, which can lead to loosening. That's called a rocking horse phenomenon, and also lack of function because the shoulder isn't stable, so you cannot move the arm effectively. Now in those cases, a reverse shoulder replacement is ideal. So what a reverse shoulder replacement does, it's done through the same incision through the shoulder, front of the shoulder, also preserving the muscles when you go in. But you simply put a ball on the socket side, okay? And that typically has a base plate component that's behind it that has some screws that are designed for ingrowth into the bone. And on the arm bone side, a stem is placed. There is movement towards stemless here as well, but that's not quite available. But regardless, you place a stem and there's a socket side with a plastic liner now on the humeral side or arm bone side. So by doing this, the stability is restored to the shoulder. So this compensates for deficient rotator cuff. And then one can still use the other remaining muscles such as the large deltoid muscle on the side of the shoulder to raise the arm up and rotate out to the side as well as the additional shoulder muscles. Now, anatomic shoulder replacements, if we go into history, have been around since the 1970s. Okay, so this was first developed by Charles Neer, was really one who first popularized this in the 1970s. And for many years, that was really our option, whether you do a ball or the ball in the socket. And that was the big controversy of what's called a hemiarthroplasty or a total shoulder. Total shoulder just means doing both sides of the joint. Then in the 1990s mainly, a little bit earlier than that, but in the '90s it became popular in France to do a reverse shoulder replacement for people who had rotator cuff deficiency. Because what happens is when you have a chronic rotator cuff tear, the ball moves around abnormally and you get arthritis as a consequence. That's called rotator cuff arthropathy or rotator cuff arthritis. And so previously we did not have a solution because people could not raise their arm with a standard shoulder replacement. But by restoring stability, the several people from France showed us that we could use a reverse shoulder replacement to restore that stability to get people to raise their arm again. That became available in the United States in 2004. It was first FDA approved, and since that time there's been an explosion really in the use of reverse shoulder replacement. Some of that has been due to expanding indications, people using it for other indications outside of just rotator cuff arthritis. Uh, another part of that has been just the widespread adoption or, uh, understanding of techniques, and then also the aging population. So if you look currently, actually the usage rates, it used to be like, for instance, in the early part of my practice, it was about 50/50 that I would do a reverse or an anatomic shoulder replacement. Actually, now it's about 70% of shoulder replacements are reverse shoulder replacement. And in people who do high volume of shoulder, it can be even greater. In fact, there are some individuals, uh, who even argue that a reverse should be done almost every single time. So why is that? Well, if you look at the problems with anatomic replacement, there's a couple of problems one can run into. One is that socket side can loosen. And when that socket side loosens, because you just have a plastic component in the bone, that can become a significant problem because it does not just fall out. It oftentimes will loosen, the plastic will be broken down by macrophages in your body, and that will lead to bone removal. And there's not a lot of bone here to, uh, support. So then when somebody does a revision or a second procedure, if necessary, it can be very, uh, difficult. The other problem is that the rotator cuff can either fail to heal at the time of the primary operation, or one can develop a rotator cuff down the line, in those years to come. And then one is left with a standard shoulder replacement, anatomic shoulder replacement, that lacks function as time goes on because the rotator cuff is not functioning effectively. So for those reasons, reverse shoulder arthroplasty has really become more common um, over time, and the usage rate is actually higher. So what are the indications for, or reasons to do, an anatomic shoulder replacement? Well, there's a couple of requirements in general. One, you of course have to have an intact rotator cuff. There are some studies that even say you can have a small full-thickness tear of the rotator cuff and do well with an anatomic shoulder replacement, but generally speaking If somebody has a full thickness tear of the rotator cuff, they are going to do better with a reverse shoulder replacement. That doesn't mean they can't do well if they have partial tearing. If you MRI anybody, it's really common to have some partial tearing, especially if you look at that on advanced imaging. So I'm talking about full thickness tears. So, um, you have to have an intact rotator cuff. And then also you have to, at the most basic level, have to have bone quality or bone stock that supports a glenoid or socket component. Okay, so sometimes the socket can wear abnormally where it wears in the back more than the front. That's called a B2 glenoid. That's the most common pathology that occurs. And if that gets too— sometimes it can be enough where you can just correctively ream a little bit to get the socket to seat, but other times it can become more severe. So you have to have an intact rotator cuff and you have to have sufficient bone stock. Okay, so with reverse replacement, the— there's a couple of major indications. One is the first one we talked about, which is rotator cuff arthropathy or rotator cuff arthritis. That's where you have a large rotator cuff tear, you have arthritis, so you restore the stability by doing the reverse shoulder replacement. Increasingly, it's used in people with primary shoulder arthritis. Who have an intact rotator cuff, but they have that socket problem. So they may have that socket problem or wear on the back of their glenoid. And as you can see here, because with reverse you have screws that go into the bone, this can withstand more force and be more stable in that scenario. One particular scenario is with what I described the B2 glenoid, where you get wear in the back of the shoulder, there tends to be, with an anatomic replacement, this phenomenon that if you place this, the ball will want to continue to wear on the back, okay? And it would want to slide back in this direction. And they can do well, people can do well initially, but then have late instability even though the rotator cuff is intact because the body wants to go where it was before. Well, with a reverse shoulder replacement, because it is semi-constrained, The ball is fixed. Now you have this plastic liner and now you have stability maintained. So as it becomes more severe, the studies show that with a reverse replacement you have more predictable, uh, results. Other indications or reasons to do a reverse shoulder replacement would be other reasons that you would have a deficient rotator cuff. An example would be after somebody breaks their shoulder or has a proximal humerus, a proximal top of the shoulder, humerus, the arm bone. They have a break that's not reconstructible. In that case, you have lots of pieces. The rotator cuff is attached there, and it's typically more predictable to do a reverse shoulder replacement. Another common reason for reverse shoulder replacement is revision. So in my practice, almost all revisions I do from an anatomic replacement are to a reverse replacement. And the reason for that is that typically in the revision scenario, the soft tissue is compromised. So there's a balancing issue. And the reverse provides that stability. So those are the 4 most common reasons that somebody does a reverse shoulder replacement or needs a reverse shoulder replacement. Now, what about the survival of the implants? How long these last? Actually, the studies show that this is pretty comparable. Um, for instance, survival, if you just look at that as the implant, is it still in and not needing to be taken out or revised for any reason? It's about 90% for both replacements at 10 years. Recently, there is some data from the Australian Joint Registry. The Australian Joint Registry is interesting because what it does is it looks at all the replacements that have been done in that country and collects all the information, and you can compare across multiple implants and multiple surgeons. So it's a captured population, which is why I like to refer to it. And in that registry, it actually turns out that at 7 years after surgery, the survival rate of a reverse shoulder replacement is slightly better than an anatomic shoulder replacement. So revision is a couple of percent lower in that study. It's roughly a 5% revision rate with a reverse and 7% with an anatomic. Now some people say, well, that's because reverse is the last operation. That may be true to some extent, but one of the other reasons could be for those reasons I mentioned, that you— they avoided rotator cuff problems or socket or glenoid loosening-sided problems. So overall, it appears that survival may be perhaps better with a reverse shoulder replacement, and that again is due to rotator cuff and glenoid loosening. Now, what about the differences in outcomes? How does somebody function afterwards? And there's been increasingly studies that have looked at this. Now, some of this has to do with design of reverse shoulder replacement, because with reverse shoulder replacements, there was a lot of different options. So when reverse shoulder replacements first when it first came out, what we saw was that there was a desire to improve fixation because there was some, actually some early designs where this fixation didn't work so well. And so initially what people did is they medialized the glenoid, put it in so there was less rotational or deforming forces. And in addition, on the humeral side, there was more of a flat angle. Okay. So what that would do, just a model, is that it would sit under like this at more of a flat angle. That would create notching on the bone here and eventually some loosening because as the plastic breaks down, you get wear and loosening of implants. Also, that would lead to limitation in range of motion. People could get it up really well 'cause they could have clearance, but they do really poorly rotating because they would impinge on the bone. Now in modern implants, it's still some variance between companies and the surgeon who uses a different type of company, but generally speaking, The socket side has moved more out or lateral. We call that lateralization. And the humeral side has moved to more matching the anatomy. There's still a little bit of variance here, but generally speaking, most of the design companies and surgeons are trying to match the anatomy more closely to do what's called a 135 implant, uh, to really get into the detail. And in here you have some slight lengthening of the arm, as you can see here. But overall, you have a relatively anatomic position. So people do very good with raising their arm overhead and out to the side. But if you look at the studies closely, there are still times where people have limitation in internal rotation. There's still some potential for impingement on this bone in the front right here. That's called the coracoid bone right here. And there's probably some restriction due to soft tissue restraint because oftentimes the rotator cuff is still attached in the back of the shoulder and that may restrict one from going forward all the way because again, there's constraint here where you're moving around a fixed point. And with a standard shoulder, our shoulder not only moves but it actually glides. So you get a motion that's really a complex motion versus moving around a fixed point that makes the shoulder the most mobile joint in the body. So in summary, when you look at range of motion, what you generally see is that people with an anatomic and reverse shoulder replacement get equal rotation out to the side and forward elevation, but people with a reverse replacement are less likely to be able to get up behind their back. Now oftentimes people accept that because the most important thing they're looking for is pain relief and the ability to do functional activities, but if somebody is really desiring motion behind the back. Or if somebody comes in with good motion behind the back already, I talk to them about these different, different results they can obtain. So I hope that overview helps you understand that reverse shoulder replacement now is the most common shoulder replacement done. The survival is equal to or better than anatomic replacement. There's some slight difference in outcomes, but overall patients do very well with either an anatomic or reverse shoulder replacement. And what's most important probably is the selection for the different implant type and the surgeon who's doing that replacement, because there's a lot of variability, and you could see some of the subtleties I talked about there. Thank you for listening.