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In total knee replacement, an incision is made in the front of the knee to allow exposure inside the joint. Once inside the joint, the cartilage that has been destroyed from the process of arthritis is removed almost like a capping on your tooth. The end of the bone is shaped to accept the components on both the femur and the Tibia. Using either robotic or manual surgical techniques, the knee is then balanced both in extension as well as flection, requiring a nice stable balanced knee replacement. The final components are then cemented into place with a type of surgical cement, which acts more like a grout going into the intricacies of the bone and hardening in place. Then a plastic component called polyethylene is inserted in between the two metal components and the knee replacement is complete.
In total knee replacement, an incision is made in the front of the knee to allow exposure inside the joint. Once inside the joint, the cartilage that has been destroyed from the process of arthritis is removed almost like a capping on your tooth. The end of the bone is shaped to accept the components on both the femur and the Tibia. Using either robotic or manual surgical techniques, the knee is then balanced both in extension as well as flection, requiring a nice stable balanced knee replacement. The final components are then cemented into place with a type of surgical cement, which acts more like a grout going into the intricacies of the bone and hardening in place. Then a plastic component called polyethylene is inserted in between the two metal components and the knee replacement is complete.
Specifically with the knee replacement surgery, there is a tool we utilize with robotic technology that allows us to create a three dimensional map of the patient's anatomy and their knee replacement. This allows us to specifically balance the knee and perform precision cuts utilizing the robot assisted device. There are two different types of robots. One requires CT and the other does not. Both robots allow for very precise alignment as well as balance for the implant with partial knee replacement. This is very critical in we have learned that the longevity of the implant is directly tied to not overloading the other side of the joint in order to not create additional arthritis on the other side where there is none presently.
Many patients will ask how long does my surgery last or how long will the implant itself last? And it used to be that the rate limiting step in joint replacement was wearing out of the plastic component in the joint. Thankfully, this has been solved by the engineers of the major joint replacement companies and so much so that it is no longer their most rate limiting step within your joint replacement. Typically, patients will require a revision surgery or a redo surgery for a reason other than that the joint just wore out on them. For instance, in 20 years if you fell down the stairs and broke the bone around the implant, that is actually more of a reason why you may require revision surgery rather than simply changing out the tires. The plastic itself wears out at about 0.1 millimeters per year. Typically, the thickness of these implants with the plastic is about six to seven millimeters thick. Therefore, theoretically giving you 60 years with this implant. Of course, this has never been proven because the implant itself hasn't been around for that long. Most of the companies will estimate that their joint replacement in terms of wear related issues would last over 30 years, but we cannot be certain at this time.
One of the most common complications following both hip and knee replacement is the formation of blood clots. Typically, we develop a plan preoperatively based on your risk of developing a blood clot. Most patients are standard risk and require simply a full dose aspirin to be taken once daily to decrease their risk of blood clots. This medicine in addition to surgical stockings, as well as getting up out of a seated position and walking multiple times throughout the day, is enough to decrease the risk of developing and DVT or blood clot in the lower leg. A blood clot can be very serious condition as DVTs can often travel up into the lungs, creating what is called a pulmonary embolism, which can be fatal. Patients who are at higher risk of developing a blood clot, either a DVT or pulmonary embolism are then placed on some medication to allow the blood to be thinned out more. Common examples of blood thinners are medications such as Eliquis, Zeralto, or even coumadin, which is used less commonly now due to the difficulties in dosing, as well as the inconvenience of multiple blood draws.
Once your orthopedic surgeon has decided you're a candidate for joint replacement surgery, there are a few things that you can do to optimize your outcome. First of all, many of my patients will undergo formal preoperative physical therapy, or we commonly refer to it as Prehab. This improves your conditioning prior to surgery, leaving you stronger going in makes you a stronger person recovering from surgery. I strongly believe in this philosophy and it really improves the patient's outcome from a rehabilitation perspective. Another way to optimize your surgery and outcomes is to control your medical conditions. Typically, we rely on the preoperative medical doctor to obtain clearance for our surgical patients. This includes managing blood sugars as well as cardiac conditions. A lot of times we rely on the medical doctor to improve the A1C value to value less than 7.0.
The most important thing for patients to be able to do prior to their surgery is to know what to expect from their surgery. Many patients come to me from other surgeons with an expectation that they will be able to play golf in just two weeks following their hip replacement surgery or ride a bike or go mountain climbing. If you have the wrong expectations following the surgery, you're bound to not be happy with your result. Joint replacement is one of the most successful surgeries in orthopedics, but it takes time to recover from your joint replacement. In hip replacement surgery, we require that the femoral acetabular components grow into the bone over time. This requires at least three months for this to happen. During this time, we want patients to abstain from very high risk activities such as high impact jumping, climbing. Those types of activities could potentially dislodge the prosthesis and ultimately decrease the chance for true bonding of the implant to the patient's native bone.
Anytime you have a surgical procedure, there are many risks associated with that procedure. A lot of the risks are actually anesthesia related, the risk of going to sleep and potentially not waking up. Thankfully that's very low in this country. In the United States and particularly at our institution, the surgery itself with hip replacement and knee replacement does have a risk of infection, neurovascular injury, stiffness, and particularly with the hips dislocation of the implant. Thankfully many of these are quite low. Anesthesia-related risks such as cardiac conditions, heart attack, pulmonary problems are higher on the list of complications and are more likely a direct result of the anesthesia itself. Other risks include loosening of the implant itself in the hip that would require deep bonding of the surface that grows into the implant and in the knees particularly it's loosening of the cement that can occur with time. Many of the risks associated with older implants were more related to wear related conditions such as wearing out of the prosthesis and would require a interval change in the prosthetic surface and bearing surfaces. This is less common these days as the implants are made with more integrity and longer lasting implants.
Complication rate for hip and knee replacement is quite low, thankfully. The incidence of infection is less than 1% for the hip replacements and a little between 1 to 2% for the knee replacements. Thankfully, all of these complication rates are quite low making this procedure one of the most successful surgeries in orthopedic surgery.
Joint replacement is actually one of the most successful surgeries in orthopedic surgery and actually one of the most successful surgeries period. The hip replacement is a slightly more successful in terms of patient satisfaction rates than the knee replacement itself, but together these surgeries have greater than 90% satisfaction rates for patients who are now living with their new replaced joint.
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