Differences and Similarities Between Knee and Hip Replacement Surgeries

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Interviewer: In this series of podcast, we're talking about hip and knee replacements and what you might need to know and what you do need to know, all the way from the beginning to the end of the process. So in this particular podcast, we're going to talk about hip and knee, the similarities and the differences, because for the most part, there are a lot of similarities. 

But there are some unique risks and challenges that might apply if you're getting a hip replacement or a knee replacement. Dr. Chris Pelt is a joint replacement expert at University of Utah Health Care in the Orthopedic Center. So first of all, let's look at the similarities between these two types of joint replacements.

Similarities Between Hip Replacement and Knee Replacement Surgery

Dr. Pelt: Hip and knee replacements are both fairly invasive surgeries. They're done in a hospital setting. Most patients will have an in-patient stay of overnight. Some patients might be eligible to go home the day of surgery and others may take a couple of extra days. In general though, they are very similar as far as the invasiveness and the risks that are associated with the surgeries. 

We do spend time in clinic and try to have patients understand that there are risks, and that's part of the reason that we don't invite every patient to simply jump right into joint replacement surgery. The benefits of the surgery, mean the potential for relieving pain and improving function, have to be greater than the likely risks that exist when you undergo any procedure, and in particular, with joint replacement.

Joint replacement is a unique surgery when compared to other surgeries in our bodies because we're using metal and plastic parts to resurface the end of our bones. The reason that's really important to understand is metal and plastic parts in our bodies don't have an immune system and they can't fight off infections on their own, and so they're at very high risk for infection-related complications. 

That being said, national averages over the last decade or so have ranged between 1 and 3% when you look at all joint replacements done throughout the country. At the University of Utah, we work really hard on our infection prevention methods and our average has been less than 1% actually over the last five years.

Joint Replacement Risks

But it is important to understand that if an infection occurs in a joint replacement, we can't simply treat it like we might if we get an infection in a different kind of surgery of our body. We can't just give an antibiotic and hope the infection goes away. Often what that means, if we do experience an infection, that we're going to be going to the operating room and there's going to be more surgeries. 

Potentially, surgeries to remove the implants that we worked so hard to place and get those taken out because we have to get the bacteria and the implants out together. So that's one of the really unique issues that's related to joint replacement, as opposed, as I mentioned, to other potential surgeries people might have throughout their body.

Besides that, there are other inherent risks of joint replacement surgery. There's a slightly increased risk for blood clots. That can happen in the legs or the lungs. We work really hard to try to prevent that. Part of the prevention is just getting people up and moving which is one of the great things about joint replacement is it does help improve their function, helps them get up and move.

We encourage our patients to get up and start walking with their therapist on the day of the surgery, and in order to decrease their pain as well as to decrease their risk for blood clots. We also use some medications to help thin the blood and also to help prevent people from getting those blood clots.

And then there are other issues that anyone could have with any surgery, whether it's a joint replacement or anything else, they might have a risk for a heart attack or strokes or other bad things that could happen medically. They are exceedingly rare. In fact, the risk of those types of bad things happening with anesthesia or joint replacement is no more and perhaps even less than the risk of them getting in a car accident on the way to the joint replacement center. So we really take a lot of effort and spend a lot of time maximizing people's health and working hard to minimize their chances of having an adverse event or a risk or a complication.

Differences Between Hip Replacement and Knee Replacement Surgery

Interviewer: So those are some of the similarities whether you're getting a knee or a hip. Now, let's look at some unique aspects of knee surgery.

Knee Replacement Surgery

Dr. Pelt: So with knee replacement surgery, it is a part of your body that has the effect of gravity. It's downhill from our heart. So knees tend to swell perhaps a little bit more. They tend to get fairly bruised after the surgery. And then most importantly, not just around the time of the surgery, but also for the life of the knee replacement, some patients will describe a more mechanical feel of the knee. They might notice some clicks. Most patients will have a patch of numbness on the outside of their knee after the incision is made for knee replacement. These are all very common things and they're a little bit unique to a knee replacement as opposed to a hip replacement.

Most patients will have substantial improvements in their pain, and again that is the whole purpose of doing the joint replacement, is to decrease peoples' pain. But it may not be completely pain-free. They may still have a little ache or swelling occasionally. They may notice the weather change. But often, they are performing well better than they had been before their joint replacement.

Hip Replacement Surgery

With hip replacement, many people will actually go on and even forget that they had it done. The hip does perform differently than the knee. It's a different type of joint, it's a ball and socket as opposed to a hinge type of a joint like a knee. So there's different types of soft tissues around it, it's a deeper joint, there's more muscles. 

In general, many patients after hip replacement after a year or more may not even remember they had it done. They become so pain-free and it becomes such a normal part of their life, so people do have those subtle differences that they notice between hip and knee replacement.

Differences in Risks

There are differences also in the risks between the two. With knee replacement, we don't much talk about the risk of dislocation or leg length, and many surgeons that will discuss hip replacement with patients may discuss these unique things. Dislocation in a ball and socket joint means the ball will pop out of the socket. That's also an exceedingly rare complication, but it is unique to the hip as opposed to the knee. 

What happens if a dislocation occurs, patients may have to go to the emergency room or come back to the hospital, see their surgeon to have it replaced or reduced without surgery. But again, the risk of that is very, very low. Less than 1% with the techniques that we use in today's approaches to minimize their chances of dislocation.

Leg lengths the surgeon can adjust slightly during a surgery, but our surgeons are working very hard and actually using X-rays during the surgery and measuring within millimeters, if not micrometers, to make sure that we're working hard to restore patient's leg lengths again so that patients don't feel like they're unequal. Many patients will come into surgery with one of their legs being longer or shorter actually because of the arthritis, and we're working to make those equal again with the hip replacement to restore that again.

Hip and knee replacement afford significant improvements in patient's quality of life, their improvement in their function, and decreases in their pain levels. There are unique differences between the two procedures. But in general, very similar risk profile and very similar improvements in patient's outcomes. 

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