According to the Journal of Bone & Joint Surgery, by 2030, the demand for primary total knee arthroplasties is projected to grow to 3.48 million procedures annually. If you’re considering a total knee or partial knee replacement, you’ll want to understand how a knee replacement is done to prepare yourself and the loved ones who may be caring for you.
Keep reading to get all the details about knee replacement surgeries—including what’s done before, during, and after the procedure for pain management—from our IBJI hip and knee replacement surgeon Alexander Tauchen, MD.
What Goes on During a Knee Replacement Procedure?
Dr. Tauchen explains how a knee replacement is done by first describing, in a nutshell, that the basic operation involves opening the skin, cutting the bone with a saw, and placing the metal and plastic implants.
First, we position the patient on the operating table and thoroughly wash their knee to prevent infections.
“The knee is draped sterilely, thoroughly cleaned, and washed to minimize the risk of infection,” he says. “We go through the skin. Below the skin is called the joint capsule. It’s there where we make an incision. Once we get through the joint capsule, a surgeon moves the knee cap to the outside of your knee. Then we’re staring down inside the knee joint.”
Orthopedic knee surgeons use retractors to visualize the area.
What Happens During a Knee Replacement Procedure
“One of the things that may surprise you about how a knee replacement is done is that a surgeon will remove the patient’s ACL in almost all cases,” Dr. Tauchen explains. “We also remove the meniscus. Once those are removed, we prepare to make the bone cuts.”
Getting a Great Fit
When it comes to how a knee replacement is done, one easy way to think of the procedure is to think of it as an operation where the arthritic ends of your knee joint bones are replaced with a combination of metal and plastic materials.
“A surgeon puts a metal cap on the end of your femur after removing the arthritic parts on the end of the bone. Then, a metal plate that is implanted on top of the tibia, with a piece of plastic placed in between,” Dr. Tauchen says.
“We cut the tibia to make a perfectly flat surface for that plate to fit on, and we make a total of five separate cuts on the femur.”
The cuts are exact in angle and depth to ensure the implant fits perfectly.
“You have to cut the bone, and the point is to remove the arthritic surface and then have the implant fit well,” Dr. Tauchen says.
Using the Right Materials
With how a knee replacement is done at IBJI, our surgeons will often pick to use cobalt-chromium, an alloy, as a material for femur implants. Additionally, they sometimes use tibias made out of titanium.
In rare cases when a patient has a metal allergy, IBJI surgeons may use a ceramic-like material instead.
During knee joint replacement, your surgeon may also use plastics unlike any used for common household goods, like children’s toys.
“This is an ultra-high molecular weight polyethylene,” Dr. Tauchen says. “The plastic molecules are cross-linked at the molecular level, making a hard, durable material with favorable wear properties.”
Testing the Knee
The next step in knee replacement surgery is “trialing the knee.”
“We will put trial pieces in first to make sure we like the knee's stability, and we’re satisfied with that,” Dr. Tauchen says. “If we’re not satisfied, we might release a little more soft tissue or even cut more bone. Then we will bring out the actual implant.”
Manufactured parts come in many different sizes. “There is a size for everybody, and the important part is to use the right size,” Dr. Tauchen says.
4 Knee Replacement Surgery Technologies
There are various ways surgeons can approach knee replacement surgery. Modern technologies are constantly advancing to improve patient outcomes.
To understand how a knee replacement is done, consider some of the following types of surgeries.
- Manual knee replacement uses specialized alignment guides (this is the most common approach nationwide)
- Computer navigation-guided knee replacement surgery uses many digital points registered on the bone to give external feedback from a computer to help with sizing and alignment
- Patient-specific implants, or PSIs, in knee replacements require a CT or MRI ahead of the surgery, and there are custom cutting guides ordered ahead of time to exactly match the patient’s knee anatomy
- Robotic-assisted knee replacement surgery involves a saw attached to a robotic arm to guide the operation
With robotic-assisted knee surgery, Dr. Tauchen explains, “at the time of surgery, you register the knee, and you use a probe and tell the computer where the knee is located in space in the room. Once you adjust the cut thickness and angles, it does not allow you to deviate from this plan when making your cuts. It’s more accurate with more precise cuts.”
Adhering the Parts
When it comes to how a knee replacement is done, cement is commonly used to attach your new knee parts.
“We cement the tibia, then we put on the femur, and the last thing we put on is the plastic,” says Dr. Tauchen.
The cement goes on like grout between the spongy, inner part of the bone.
Bone spurs are removed before cementing. The result is, according to Dr. Tauchen, “metal on the femur touching the plastic on the tibia. There are now no nerve endings on the articulating surfaces, so there’s no more pain.”
Some orthopedic surgeons are performing cementless procedures, which is considered a new technology advancement in knee replacements.
“With cement, you coat the bone, and—once it dries—it doesn't come off in the short term,” Dr. Tauchen says. “With a press-fit knee replacement, you wedge the implants into or onto the bone. Since bone is a living, dynamic thing, your bone will actually grow onto the back surface of that implant.”
Pros and Cons of Cementing in Knee Replacement Surgery
“When I talk to patients about how a knee replacement is done, I explain that implants shouldn’t be coming loose any time soon.” Dr. Tauchen explains. “In the short term, the cementless implants may come loose, but over time the implants will grow together with the bone.”
Press-fit technology is most appropriate for young, healthy patients with good bone quality. Cement is a better option for older patients with poor bone quality.
Inpatient vs. Outpatient Knee Surgery
Today, very few patients stay longer than one night in the hospital unless they are elderly with no help at home or in a unique situation, according to Dr. Tauchen.
When discussing how a knee replacement is done, Dr. Tauchen believes in an upfront and honest approach for the best patient outcome.
“This is a painful operation,” he says. “If people go into a knee replacement, it is a big deal. It hurts for the first couple of days but improves after a few weeks. People seem to turn a corner by two to four weeks, and their pain is much more manageable.”
Pain associated with knee replacement surgery is managed as effectively as possible.
“We usually premedicated patients in the holding area before they go into surgery,” Dr. Tauchen says.
“When it comes to how a knee replacement is done, surgeons often preload patients with an IV Tylenol or a narcotic to get them ahead of the pain. The other thing that is done is a peripheral nerve block, which is an ultrasound-guided numbing agent that may last up to 24 hours.”
Patients receive intra-articular injections during surgery. At various points in the surgery, a numbing medicine cocktail is injected all around the knee. The cocktail contains an anti-inflammatory to help control pain around the lining of the knee.
“These injections and blocks help to control the pain for up to 12 to 24 hours, but then the pain often increases after those things wear off,” says Dr. Tauchen.
“After that, some people can take oral Tylenol for mild to moderate pain. There’s also IV Tylenol and narcotics (e.g., Percocet, Norco, and Oxycodone). Multimodal pain control is a big thing. We sometimes use Gabapentin and Neurontin, which work on nerves, or Celebrex, an anti-inflammatory or NSAID.”
Morphine or another IV narcotic can be used in cases of extreme pain.
With multi-modal pain control that attacks nerves and inflammation, the patient is made as comfortable as possible. “We try to minimize the use of narcotics as much as possible,” Dr. Tauchen says.
FAQs About How a Knee Replacement Is Done
Below, Dr. Tauchen fields multiple questions about how a knee replacement is done.
Is the Knee Cap Removed During Knee Replacement Surgery?
Some surgeons choose to replace the knee cap routinely, some replace it occasionally, and some never replace it.
“I resurface the knee cap every single time,” Dr. Tauchen says, adding that there can be arthritis on the back of the knee cap.
How Is Partial Knee Replacement Different From Total?
In terms of how a knee replacement is done, it’s essential to understand the different parts of your knee.
Your knee is divided into three compartments: the medial, lateral, and patellofemoral. For certain patients, if they happen to have arthritis in only one part of the knee, they would be a good candidate for a partial knee replacement. This leaves more of the original knee intact.
“Theoretically, it should be an easier recovery,” says Dr. Tauchen. “There’s a smaller incision and less trauma to the knee. We still have to make bone cuts, put implants in, and use cutting guides, but we’re only doing it in an isolated compartment.”
Are You Awake During a Knee Replacement?
You typically don’t have general anesthesia, but you’re given a sedating medicine, so you’re taking a really good nap. Anesthesia-wise, total joint replacement used to be done under general anesthesia. Now it’s most often done with regional anesthesia in the form of a spinal nerve block.
How Long Does Knee Replacement Surgery Take?
How a knee replacement is done by most surgeons takes, on average, around 60 minutes.
Which Muscles Does a Surgeon Cut During Knee Replacement Surgery?
Depending on how a surgeon goes into the knee, sometimes a muscle—called the vastus medialis—must be cut. It is part of your quadriceps.
Do You Need a Catheter During Knee Replacement Surgery?
We’ve generally gotten away from that, and it’s only used in rare circumstances.
How Painful Is Having Knee Replacement Surgery?
It’s typically a pretty painful operation, and patients should go into it expecting that for the first few days. However, there are a variety of medications that can make you as comfortable as possible.
Is There an Age Limit for Knee Replacement Surgery?
Not really. The youngest patients—in their 30s and 40s—are those who tend to have pretty bad arthritis. We perform this surgery on patients as old as the early 90s.
What Happens to Your Kneecap When You Get a Total Knee Replacement?
Based on the amount of arthritis under the kneecap, it’s typically replaced but not always. It varies with the surgeon.
Is Knee Replacement Considered Major Surgery?
Yes, no matter how a knee replacement is done, it’s considered major surgery.
Learn More About IBJI’s Knee Replacement Surgeons
More than 90% of modern total knee replacements are still functioning well 15 years after the surgery, according to research from the American Academy of Orthopedic Surgeons.
If your knee pain affects your quality of life, look to IBJI’s highly trained surgeons and doctors. IBJI offers convenient locations across the Chicagoland area, and we are experts in arthritis treatment, pain management, and total knee joint replacement surgery.