Knee Replacement Surgery: An Overview

Medically Reviewed by Jabeen Begum, MD on December 18, 2024
Written by Hallie Levine
14 min read

You can't move like you used to. It's painful to walk the dog, climb a flight of stairs, or simply get out of a chair. You've tried medicines, injections, and physical therapy. Nothing seems to work. If that's the case, it could be time to consider knee replacement surgery.

Also known as arthroplasty, knee replacement surgery is one of the most common bone surgeries in the U.S. It can help ease the pain caused by severe arthritis. It also may help you move more freely. U.S. doctors perform more than 600,000 knee replacement surgeries each year, many of which are now being done robotically.

During surgery, an orthopedic surgeon removes the damaged part of the knee and replaces it with an artificial joint made of metal and plastic. The artificial joint is then attached to the thigh bone, shin, and kneecap with a special material, such as acrylic cement.

Osteoarthritis is the main reason why people go for knee replacement surgery. The age-related condition is very common and occurs when cartilage — the cushion between the knee and the bone joints — breaks down. If your osteoarthritis is so painful it's hard to walk or climb stairs or you notice it even when you sit or lie down, you may want to consider a knee replacement.

Other reasons include:

  • Inflammatory arthritis. The most common form of inflammatory arthritis is rheumatoid arthritis. Your immune system attacks the tissues that line your knee joint. It damages your cartilage and causes pain and stiffness.
  • Deformities. People with bowed legs or "knock-knees" often get surgery to restore the position of the knee.
  • Knee injuries. A broken bone or torn ligaments around the knee sometimes will cause the cartilage in your knee to break down faster. This can lead to arthritis that causes great pain and limits your movement.

The initial treatment for all of the above are conservative measures like over-the-counter pain relievers, steroid injections, or physical therapy. But sometimes, they aren't enough to relieve discomfort. These conditions all tend to progress over time, which means your pain may worsen, and you may not have as good of a response to these treatments. In these cases, it's reasonable to consider knee replacement surgery.

There are five types of knee replacement surgery:

Total knee replacement surgery

This is the most common form. Your surgeon replaces the surfaces of the thigh bone and shinbone that connects to the knee.

Partial knee replacement surgery

If arthritis affects only one side of your knee, this surgery may be a possibility. However, it's only right for you if you have strong knee ligaments and the rest of the cartilage in the knee is normal. Partial knee replacement can be performed through a smaller cut than is needed for total knee replacement.

Patellofemoral replacement surgery

This replaces only the under-surface of the kneecap and the groove the kneecap sits in. This can be very effective for people with chronic kneecap arthritis.

Complex (or revision) knee replacement surgery

This procedure may be needed if you have very severe arthritis or if you've already had two or three knee replacement surgeries.

Cartilage restoration surgery

Sometimes when the knee only has an isolated area of injury or wear this area can be replaced with a living cartilage graft or cells which grow into cartilage.

Knee replacement surgery has become so precise that doctors can choose from a variety of knee designs that suit your height, weight, and activity level. The implants, as they are called, are made from a variety of materials, including metal, ceramic, or plastic. They are built to allow easy movement. Some implants are made just for women — to closely match their anatomy.

Implant materials

Implants are made from metal, ceramic, and plastic and typically weigh between 15 and 20 ounces (roughly a pound to 1¼ pounds). All implants have three main parts:

  1. Tibial component. This is a flat metal platform with a cushion of strong plastic that attaches directly to the shinbone. It may also have a stem that inserts into the center of the shinbone.
  2. Femoral component. It's a piece of metal that curves around your thigh bone. It's grooved, to help your kneecap move up and down.
  3. Patellar component. This is a dome-shaped piece of plastic that mimics the shape of your kneecap. It's not always needed.

Implant designs

There are three types of implant design:

Nonconstrained or cruciate-retaining implant. This implant keeps your posterior cruciate ligament (PCL), a knee ligament that connects your upper and lower leg bones. For this to work, your PCL needs to be strong enough to support knee movements such as bending, straightening, and rotating. Your anterior cruciate ligament (ACL), which connects your thigh bone to your shinbone, is still removed.

Semi-constrained or posterior-stabilized implant. Your surgeon may want to use this implant if your PCL isn't strong enough and needs to be removed along with your ACL. This implant has two parts, for both your thigh bone and shinbone. They are connected together by a hinge that replaces your PCL and ACL.

Constrained or hinged implant. This type of an implant has a hinge and is attached to the bone on each side. Your surgeon will use it if other knee ligaments, like your medial and lateral ligaments, aren't strong enough to support your knee. They may also use it if you have a significant knee deformity like knock-knees or bow legs.

How long do knee replacement implants last?

Doctors first started replacing knees in the early 1970s. Back then, surgeons said the new knees would last about a decade or so. Research suggests that just over 80% of all knee implants will last 25 years. Younger people are more likely to live longer and have a more active lifestyle, which may mean their implant needs to be replaced earlier. That's one reason why doctors are more cautious about recommending knee replacement in people younger than 50 years.

Knee replacement surgery can be life changing for many people. But it's not a miracle cure. Some things to keep in mind include:

Have realistic expectations. If you've never been a runner, don't expect that you'll be able to run a half marathon on your bionic knee. In fact, surgeons recommend that you avoid high-impact activities like running or jumping for the rest of your life. Otherwise, you can damage or wear out your knee replacement implant. You'll be able to do low-impact sports such as walking, swimming, golf, biking, and easy hikes.

Choose your surgeon carefully. The best surgeon isn't just one who takes your insurance. Your primary care doctor or rheumatologist may be able to refer you to someone that they've worked closely with before. Make sure that they are board certified in orthopedic surgery and that they did a fellowship in joint replacement surgery.

Expect some pain during recovery. After surgery, you will have some pain. It's a normal part of recovery. Your doctor may prescribe medications called opioids to help relieve discomfort. They have side effects, though, and can be addictive. Follow your doctor's directions carefully and stop them as soon as you start to feel better.

Know you'll need physical therapy. Your surgeon may want you to start as soon as the day after surgery. It's a key part of your recovery so that you can bend and straighten your knee and strengthen your leg muscles.

Dangers of delaying knee replacement surgery

It's not necessarily dangerous to delay knee replacement surgery. But it may affect your quality of life. Research shows that about 90% of people put off knee replacement surgery for longer than is necessary. There are a few reasons why you don't want to delay it:

  • It affects your mobility. If your knee pain gets very bad, you won't be able to straighten out your knee. This can affect your ability to walk and do everyday activities.
  • It raises the risk of other health problems. If you can't be active, you're at a greater risk to develop complications such as heart disease.
  • You don't get as many benefits. The longer you wait, the less mobility you'll get back when you do have the surgery.

You don't want to do surgery too early, either. About 25% of knee surgeries are done prematurely, which means you are more likely to have complications or need a second surgery.

Knee replacement surgery cost

The cost of an average knee replacement — including surgery, hospitalization, and medications — is about $20,000 in the U.S. Health insurance plans like Medicare generally pick up about 80% of the cost. How much you pay out of pocket depends on your health insurance, including your co-payments and deductibles.

How to prepare for knee replacement surgery

Before you have a knee replacement, you'll need a medical checkup to make sure that you are healthy enough for the procedure. This usually includes:

  • A physical exam
  • Blood and urine tests
  • EKG to check your heart function
  • Medication review; you may need to temporarily stop some prescription or over-the-counter drugs before your surgery.

Your surgeon may want you to get any major dental work like tooth removal done before your surgery. You're more likely to get an infection after a joint replacement.

You'll also need someone to stay with you at home to help you cook, bathe, shop, and do laundry for the first few weeks after surgery. If you don't have anyone to assist you, the hospital or center where you will have surgery can help you hire someone or arrange a short stay in an extended care facility.

You will also need to prepare your home so you can have a safe recovery. Things to do include:

  • Buy a raised toilet seat and shower chair
  • Install safety bars on your stairs and in your bathrooms
  • Remove loose carpet and electrical cords
  • Create a temporary bedroom on the first floor, so you don't have to climb stairs

Knee replacement surgery takes place in an operating room in a hospital or outpatient surgery center. You will be given either general anesthesia, where you're put to sleep, or spinal or epidural anesthesia to numb you from the waist down. You may also be given a nerve block to reduce pain right after surgery.

During the operation, your surgeon will remove damaged cartilage and bone and replace them with the new implant. After surgery, you'll be watched carefully in a recovery room for several hours while you recover from anesthesia. Once you fully wake up, you'll either be admitted to the hospital for a night or two, or if your surgery was done in an outpatient clinic, you'll be discharged home.

Knee replacement surgery usually takes one to two hours. After surgery, you'll need to be monitored for several hours at the hospital or surgical center to make sure you fully recover from anesthesia.

What to expect during the hospital stay

You may need to stay in the hospital for one or two nights after your knee replacement surgery. In general, you can expect the following:

Medications to relieve pain. Your medical team will most likely have you take:

  • Nonsteroidal anti-inflammatory drugs to manage pain and reduce swelling and inflammation
  • Acetaminophen for pain relief
  • Aspirin to help prevent blood clots

If you're still in a lot of pain, they may have you take an opioid for a short period to relieve discomfort and help you sleep.

Your medical team will also want you to get up and move as soon as possible to lower leg and knee swelling and prevent blood clots. If you can't stand up, you'll do gentle foot and ankle exercises in bed. You'll also be encouraged to take frequent deep breaths to help prevent pneumonia.

It may take months to fully recover from knee replacement surgery. But there are things you can do to speed up the process, like make sure you start to move as soon as possible and do physical therapy.

Total knee replacement recovery

It's different for everyone. But most people are able to walk without a walker or cane about six weeks after they have a total knee replacement. To reach this goal, it's important to do a home activity program under the guidance of your surgeon and physical therapist. This usually includes:

  • A slow return to walking. At first, you will just walk around your home. But as pain lowers, you will begin to walk outdoors to raise mobility.
  • A gradual return to activities such as stair climbing.
  • Specific daily exercises to improve stability and range of motion in your knee.

You should be able to drive a car again within about four to six weeks. You will need to be off of any opioid pain medications and be able to bend your knee enough so that you can get in and sit in your car without too much pain.

Tips for recovery at home

You will gradually feel better and stronger each day after your surgery. But the following tips can help enhance your recovery:

Take care of your incision. You may have stitches or staples around your wound. Keep it dry and covered for as long as your doctor tells you to. Otherwise, it could get infected. Once you can get it wet when you shower or bathe, wash it gently with soap and water and pat it dry. Your doctor will let you know if you need to put antibiotic ointment on it and/or cover it with a bandage or gauze.

Eat healthfully. You will need a balanced diet to heal completely. Your doctor may also recommend an iron supplement.

Look for symptoms of a blood clot. If you notice warning signs such as calf pain, redness, or tenderness around your knee or new swelling in your lower leg, let your doctor know immediately.

Watch for signs of infection. These include fever; chills; and redness, tenderness, and swelling around the wound.

Use your cane or walker. You're more vulnerable to a fall the first few weeks after surgery. You don't want to slip and need a repeat surgery. Use a cane or walker when you move around the house and handrails in the bathroom. Don't try to go up or down the stairs until you feel strong enough. Your PT can help you figure out when it's safe.

Take all your medications as directed. Follow the pain management plan your doctor or nurse has recommended. Your doctor may prescribe blood thinner medications to help prevent blood clots.

Adjust your sleeping style. Put a pillow under the foot of the leg that's just had a knee replacement. It will keep your knee straight and improve flexibility.

Knee replacement surgery is considered very safe. But anywhere from 2%-5% of patients experience complications. They include:

  • Blood clots
  • Infection
  • Dislocated kneecap
  • Nerve or blood vessel damage
  • Excessive bleeding
  • Broken or loose implant
  • Joint stiffness
  • Reaction to implant

You may be able to reduce the risk of some of these complications if you only have one knee replacement done at a time. Research shows that people who have both knees done at the same time are more likely to experience blood clots, pulmonary embolism (where blood clots travel to the lungs), stroke, and respiratory failure and are more likely to need a blood transfusion. They're also more likely to be readmitted to the hospital within three months.

Most people are very satisfied with their knee replacements. Here are some things to know about your new life with one:

  • You'll want to stay active. Low-impact activities like walks, hikes, bike rides, and swimming will help keep the muscles, tendons, and ligaments around your knee healthy and strong.
  • Don't forget resistance training. It will keep lower leg muscles strong and improve strength and balance to reduce the risk of falls which could damage your implant.
  • Talk to your dentist. If you have a major dental procedure, you may need to go on antibiotics beforehand.
  • Don't worry about strange noises. Your knee may click when you bend or walk. That's normal and often gets better with time.
  • Alert airport security. If you go through a metal detector, your knee implant may set it off. Let staff know you have one.
  • Realize a knee replacement isn't perfect. You may notice some stiffness and discomfort with your knee implant, especially when you kneel. About 15% of people will still experience persistent pain.

How to extend the life of your knee replacement

You can expect your knee replacement to last at least 20 years. Here's what you can do to help ensure it stays in good shape:

Don't overdo it. You'll need to avoid sports where you need to run, jerk, twist, or pull. That means you should not downhill ski, run, or play contact sports like football.

Limit what you lift. Ask your partner to carry in heavy groceries and take out the garbage. These activities put too much load on your new knee.

Stay at a healthy weight. People who have obesity are more likely to experience complications with a joint replacement.

Don't get have surgery too early. People who have knee replacement surgery before the age of 50 tend to have a more active lifestyle. This can put strain on your knee implant and wear it out earlier.

Knee replacement surgery is a procedure in which parts of your knee joint are replaced with artificial ones. The main reason that it's done is because of pain and stiffness from arthritis such as osteoarthritis. It's best to do it after you've tried other, more conservative strategies like weight loss, exercise and physical therapy, over-the-counter pain relievers, and injections. A knee replacement surgery is performed in a hospital or outpatient center under anesthesia. You'll begin physical therapy within days or even hours of your surgery. Most people are able to walk on their own after about six weeks.

Is a knee replacement painful?

It's normal to experience some pain in the days and even weeks after knee replacement surgery. But most people report that they have much less pain and are able to move better after surgery.

How serious is knee replacement surgery?

A knee replacement is major surgery that may require you to stay for a night or two in the hospital. It has a 2%-5% complication rate. Complications include blood clots, infection, bleeding, and joint stiffness.

What's the best age to have knee replacement surgery?

In general, doctors try not to recommend knee replacement surgery for anyone younger than 50 years. They tend to have not as good outcomes as older people. One study found that people older than 75 years reported the biggest improvements in pain, function, and overall quality of life.

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