The knee joint is a gliding joint that can be thought of as a hinge and platform. The top part of the knee joint is the end of the femur (thigh bone), and this hinges on the tibial plateau (top part of the shin bone). The knee is surgically divided into three compartments: the medial (inside of the knee/closer to center of the body), the lateral (outside of the knee), and the patellofemoral compartment (behind the knee cap and in front of the end of the femur). When only one compartment is affected by arthritis (uncommon), and all of the ligaments (connect the bones together) function well, you may be a candidate for a partial knee replacement; however more commonly, the arthritis exists in multiple compartments, and a total knee replacement is the most complete option for symptomatic knee arthritis. Your surgeon will make a recommendation based on which type of knee replacement is best for you considering the risk of progression of arthritis in less affected compartments. The goal of this would be to reduce the long term need for additional invasive surgeries depending on your goals, surgical risks and current limitations.
Total knee replacement surgery starts with removing the ends of the bones where the arthritis exists and creating flat surfaces for the implants to adhere/affix. Usually this entails a flat cut of the tibia to make this even, and then several cuts on the femur since the end of the femur has two humps called condyles.
The femur is usually cut in 4 places to create flat surfaces. These are the anterior, posterior, anterior chamfer, and posterior chamfer cuts. These are precisely set according to a jig, which is matched with an implant so that the cuts match the inside of the implant. On the femur side, the implant caps the end of the bone, and is called the femoral component. On the tibial side, the implant matches the femoral component so that this can hinge, pivot and glide for create smooth motion of the joint. It is important to understand that while many implants aim to mimic or improve the motion of the native (your original) joint, nothing will feel exactly like the normal joint.
The tibial component (bottom part of the total joint) sits on top of the flat bone cut. Then, a polyethylene insert (sterilely processed plastic) which is manufactured to click precisely in place, is set onto the tibial component. The bearing surface of the joint is femoral component articulating with the tibial insert, which sits on top of the metal tibial component.
Most commonly the patella is resurfaced, meaning that the back of the knee cap where there is cartilage is cut off in a flat cut. Then, a plastic patellar component, sometimes called a “button” is either cemented or pressed in place (if it has a metal backing). Sometimes, if the patella is too thin, it will be denervated and left alone.
Sometimes cement is necessary for best fixation of the implant to the bone. This can be on the femoral side, the tibial side, behind the patella or any combination of the above depending on your bone quality, the implants utilized, the surgical method, and/or surgeon preference.
Knee replacement implants come from different manufacturers, and have different designs similar to makes and models of cars. Although knee replacement surgery is one of the most common elective procedures performed, it is not a one size fits all surgery. Therefore, different patients will require different “makes and models” of their implants depending on factors such as their anatomy, bone strength, and metal sensitivity. Your surgeon will pick the implant(s) based off of these considerations, and preference for implant system(s).
Your surgeon may use a robot to assist with parts of the surgery. For knee replacement surgery, the robot is used for precise bone resection on the tibial and femoral sides.The use of a robot requires advanced imaging such as a CT scan done at least two weeks prior to the scheduled surgery. This allows the surgeon to create a personalized plan for your surgery and template the position of your implants based on your own anatomy before you even go to the operating room! You can think of the robot as a stable “extra arm” that the surgeon uses to make the surgery easier, and more accurate. Using the robot can also decrease the number of x rays needed to ensure precise placement of components.
Although minimally invasive joint replacement surgery sounds like less surgery, it is actually the same amount of surgery through a smaller incision. For knee replacement surgery, this is typically a subvastus (quadriceps sparing) approach which has a proposed benefit of decreased pain early after surgery. This is not always an appropriate option for everyone as the primary objective is to perform an effective surgery safely and efficiently. Although there are benefits to minimally invasive surgeries such as smaller scars and possibly some muscle sparing, these things are not as important as making sure the joint replacement goes in correctly. The biggest obstacle to a minimally invasive approach is body size, weight and habitus. If minimally invasive surgery does not work for your body type, the surgeon will choose the safest incision for your body to ensure a successful joint replacement surgery.
If you have had a steroid injection into your hip or knee joint in the last 3 months, you will have to wait until at least 3 months following the injection for surgery. Steroid injections within a 3 month period prior to joint replacement surgery puts you at higher risk for prosthetic joint infection.
Dr. Lee adheres to these nationally and association recommended clinical practice guidelines recommended by the American Association of Hip and Knee Surgeons (AAHKS):
For patients taking immunosuppressive medication, please consult the following guidelines for timing of cessation prior to surgery.
At discharge you will receive a post op folder with instructions on how to care for your dressings and when you may bath or shower. We ask that you do not remove your dressings unless they are saturated or leaking. If you are unsure, please review our instructional videos and call if needed. The post op folder will also include your medication instructions, a Persons With Disabilities parking privileges application and your hip arthroscopy photos. There is a pain/medication tracking sheet you will be asked to fill out and bring to the first post op appointment. A hip preservation team contact list will also be provided; use this to reach out with urgent matters.