Total knee replacement is otherwise known as total knee arthroplasty, TKA. It is one of the most popular surgeries done in Canada. In 2010-2011 there were 50,733 acute care hospitalizations for TKA’s. These surgeries are routine. Let’s give you a little bit of insight into what happens with a total knee replacement, during and after surgery. But first let’s go over a little bit of information about the knee.
The knee is the middle joint in the leg. It sits between the femur, the thigh bone, and the tibia, the shin bone. The far end on the femur has the femoral condyles, rounded ends, that sit on the tibial plateau. If the bone sat directly on the other bone, there would be no need of a knee replacement. However, this is not that case, the end of the femur sits on the meniscus in the knee. The meniscus is cartilage. Cartilage is one of the shock absorbers of the body. When you run and walk, the impact of the foot on the ground travels up the tibia, to and through the knee joint, up the femur and into the pelvis. The meniscus helps to absorb the shock. In addition, the only cartilage is not on the tibia but the end of the femur that is in contact with the meniscus is covered in cartilage. The cartilage is called hyaline cartilage. It is very smooth and very slippery, in fact is more slippery than a freshly polished ice surface. Normally, there is minimal friction between the knee meniscus and the cartilage at the end of the femur. The knee joint has a capsule around it and it is filled with fluid. This fluid is called synovial fluid and it does a couple of things. It lubricates the joint and the cartilage, to keep it nice and smooth. It provides nutrition to the cartilage, we think this can occur through compression and distraction. An example of compression and distraction of the knee joint happens with simple walking. When you take weight onto your foot, the femur pushes down on the meniscus, compression, and when your leg is swinging from back to front, the knee joint is distracted and allows fresh fluid to go between the femur and tibia. There are some things that can change this relationship…
Injury can change things with your knee joint. If you have a fracture, broken bone, that goes into the knee joint, that can impact the cartilage health. For example, if you break your femur and the broken part of the bone actually goes into the knee joint, there will most likely be issues down the road for that knee. Especially, if the cartilage rips. Yikes! The good news is that fractures this severe are not common. However, tibial plateau fractures are more common. They are a crack at the top of the tibia and go downwards into tibia bone. I have seen these done on someone that has fallen on an extended knee and some soccer players twisting away.
In addition, injury to the cartilage itself, a meniscal tear can cause issues down the road. About the outer 25% of the cartilage in the knee has a blood supply to it. So if you are lucky enough to tear the outer part of the cartilage and you see a surgeon before it tears more, you might be saved! The surgeons will usually stitch up the meniscus with a tear on the outer edge and it will heal itself! But what if the tear is on the inner 75% of the meniscus? Well, that is not so good… You will see a surgeon and they probably will do surgery on you and simply cut out that part of the meniscus. Let it heal for a 3-4 weeks and you can get on with your life. There was a large study done in 2015, that showed, there was no difference between groups that had meniscus surgery and that did not have surgery, only physiotherapy. Sounds great in theory however, when your knee is in acute pain, meniscus is caught and not able to move as well as very sore, you really wish for surgery to get that piece of cartilage that is catching, removed. The research was done very well but when it is acutely flared up, let’s get real, surgery can help a lot. The only issue is finding a surgeon that can see and operate on you, ASAP.
Arthritis of the knee joint. What is arthritis of the knee? It is when there is degeneration of the cartilage of the knee joint. This can be seen on x-ray… Well actually it cannot. Please let me explain. What you see on x-ray are the bones, not the soft tissue, ie cartilage or muscles. When you look at a knee x-ray there should be a nice space between the femur and the tibia, that is where the cartilage is. If the space is missing, ie it looks like the bones are touching, there is a lot of degeneration of the cartilage of the meniscus. You can see the bones close together but you cannot see the cartilage itself in the knee joint.
Knee arthritis is a major reason of people getting a TKA. What causes arthritis in the knee? Well anything mentioned in the paragraph above, well two paragraphs above, is a good place to start. Basically any type of rip or tear of the meniscus, getting part of the meniscus removed or another traumatic injury to the knee, ie ACL tear, will start you down the road of having knee arthritis. Building strong muscles around the knee and hip joint will also help to absorb shock and forces going through the knee joint and possibly slow down or stop the progression of the arthritis. We know the stronger the muscles, around the knee and hip joints, are before going into surgery, the faster the recovery post surgery. However, most people post surgery wonder why they did the exercises because the knee does not work really well, right after surgery. I can honestly say that it does make a huge difference. I have worked on the orthopaedic surgical floor of Kelowna General Hospital for a few years now. But I am jumping too far ahead of myself.
So what happens in a knee replacement? It is not very pretty, let me tell you. If you ever see a full TKA surgery, you know why the clients are sore after. I have not seen a total knee replacement surgery in a number of years, but I see the recipients of the surgeries quite often in Kelowna General Hospital. I work part time on the Orthopaedic floor of Kelowna General Hospital. Every week there are at least 30 total hip and knee surgeries, combined. But I digress. Below is an animated video of a total knee replacement.
The basic procedure, and this can change surgeon to surgeon, is this, not talked about in any order. The surgeon puts a guide on the tibia, the shin bone and cuts off the top of the tibia, the cartilage and part of the bone. This is important because next he or she pound in the metal implant on top of the tibia in which the femur will move on. The reason it is important to cut off some of the bone, is that the implant and bone will grow together making them one, much stronger together. Then the surgeon turns their attention to the end of the femur. They attach guides to the femur and cut off the end of the end of the bone. They do it in five angled cuts. The surgeon then pounds in the metal implant into the end of the femur. After that, the surgeon, then may or may not resurface the back of the kneecap, the patella. Sometimes, if the backside of the patella is really worn down, it will be cut off and an implant will be attached. Or other times, the surgeon may simply smooth out the cartilage. During a total knee replacement, the surgeon maybe able to change the angle of the knee very slightly, if the person was knock-kneed or bowlegged.
This video is an animated version of a total knee replacement.
The knee is then stapled up, wrapped up and sent to the recovery room. The operation itself takes about 90 minutes and the client typically stays in the recovery room, 2-3 hours. We see the clients up on the floor, 4W, three to four and half hours post operation.
That is when the really work begins for the clients. I have heard many times, “If I knew it was going to be this painful after surgery, I would not have gone through with it”. Clients that have a TKA done are typically very painful for the first couple of days and that is with strong pain killers in their system. In fact, more painful than client that have a total hip replacement. If you think about it, the body does not know what happened is good. The body knows it was cut open, bone sawed up, metal pounded in, then stapled up. There is good reason to be sore!
After the client comes up to the acute surgical floor, is when the physiotherapist gets involved. Typically the day of the surgery is counted as day zero. As long as the client can feel their surgical leg and can wiggle their toes we can work with them. If the client cannot feel their leg or wiggle their toes, I try to just pop in and say hi to them and go over the exercises and let them know what to expect. There are three exercises in which we do with the client, a heel slide, quads setting and quads over a roll. As well, I might get them up standing and possibly ambulate using a walker. How many times has someone asked me to get them up and when they stand up they just about pass out? Way too many times, it is very common. For this reason, I am not eager to get people up standing day zero.
Day one, is the day after their surgery. Typically, people with TKA’s find that the surgical leg is much more painful on day one. Many people are surprised about this. Unfortunately, I have to tell them that is normal. Day one, we go through all the exercises, as much as they can handle and go for a walk. The client do not walk by themself, I am not that mean. They use a 2 wheeled walker to help take the weight off their sore leg. The client’s are normally very nervous to ambulate because of the pain that happens during the exercises. However, walking is normally less painful and some people are quite surprised. Most people after a TKA are WBAT. WBAT = weight bearing as tolerated. What that means is that the person can take as much weight on their new knee as they would like. I always tell my clients that they can take as much weight on your new leg, it may hurt but you are not harming anything. I find this to be a very important statement. Simply because if you start walking and it hurts, people think that they are doing damage, which causes the pain. Letting the client’s know that pain does not equal damage to the knee is very helpful. Typically people are seen twice the first day after surgery.
Day two, is when the rehabilitation assistant, RA, comes to see the client. The RA’s will do the exercises with the client, get them up walking and do the stairs with the client. Some clients do not want to do stairs because they do not have stairs in their house or condo. What I tell them is that we live in a world of stairs. Their house may not have stairs but just wait until you have to step up on the curb or to church… The vast majority of people go home on day two post op.
It typically takes 6 – 12 weeks for the knee to heal completely. However, it can take up to a year or more to strengthen and regain the muscle lost in the operation.
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