A knee replacement removes damaged bone and cartilage and replaces it with metal and plastic parts

A knee replacement, also called knee arthroplasty, is surgery to remove the worn surfaces of your knee joint and install artificial parts in their place. The surgeon cuts away the damaged ends of your thighbone, shinbone, and kneecap, then attaches metal components to those bones. A plastic spacer goes between the metal parts to create a new, smooth joint surface. The whole procedure typically takes one to three hours, and you go home the same day or stay overnight depending on your surgeon's plan and your overall health.

The surgery is most common for people with severe arthritis — usually osteoarthritis, where the cartilage has worn down over time. It is also done after major knee injuries, failed previous surgeries, or conditions like rheumatoid arthritis that damage the joint. Your doctor will usually recommend it only after other treatments like physical therapy, injections, or anti-inflammatory medication have stopped working.

Key Takeaways

  • A knee replacement removes damaged bone and cartilage and replaces them with metal and plastic parts that mimic a healthy joint.
  • The surgery takes one to three hours and most people go home the same day or stay one night in the hospital.
  • Recovery takes three to six months before you can return to normal activities, though some improvement happens in the first few weeks.
  • Physical therapy starts when ready after surgery and continues for several weeks to restore strength and movement.
  • Artificial knees typically last 15 to 20 years, after which revision surgery may be needed if the parts wear out.

What the surgeon does during the procedure

The surgeon makes an incision down the front of your knee, usually 8 to 10 inches long. They move the kneecap to the side to reach the joint underneath. Using specialized cutting guides, they remove the damaged cartilage and a thin layer of bone from the end of your thighbone and the top of your shinbone.

Metal components — typically made of cobalt-chrome or titanium — are then attached to the cut bone surfaces. These metal parts recreate the shape of a healthy knee joint. A plastic spacer, usually made of polyethylene, sits between the metal parts on your shinbone and thighbone. The kneecap may also get a plastic button attached to its back surface, or the surgeon may decide to leave it as is. The incision is closed with stitches or staples, and you are wrapped in a bandage.

Hospital stay and when ready recovery

Most knee replacement patients go home the same day or after one night in the hospital. Before you leave, the surgical team will make sure you can move your knee slightly, walk with crutches or a walker, and manage pain with medication. You will receive instructions on how to care for your incision, when to take your medications, and what activities to avoid.

Pain and swelling are normal for the first few weeks. You will likely wear a compression stocking or wrap to reduce swelling and prevent blood clots. Your doctor may prescribe blood thinners for a short time after surgery to lower clot risk. Most people need pain medication for the first two to four weeks, then switch to over-the-counter options as healing progresses.

Physical therapy and regaining movement

Physical therapy begins within hours or days of surgery, sometimes while you are still in the hospital. A therapist will show you exercises to do at home and may see you in an outpatient clinic two to three times per week for the first month or two. Early exercises focus on bending and straightening your knee, walking, and reducing swelling.

By two to three weeks after surgery, most people can walk without a walker and climb stairs with a handrail. By six weeks, many can drive again if they are off strong pain medication and can move their knee enough to operate the pedals. Full recovery — meaning you can do most normal activities without pain or limitation — typically takes three to six months. Some people continue to see gradual improvement for up to a year.

What you can and cannot do after surgery

In the first six weeks, avoid high-impact activities like running, jumping, or sports. You should not kneel on the operated knee for at least three months. Swimming and walking are usually safe after the incision has fully healed, typically four to six weeks after surgery. Cycling on a stationary bike often starts around six weeks.

Most people can return to desk work within two to four weeks if they can keep their leg elevated and take breaks to move. Jobs that require standing all day or heavy lifting may take longer — often eight to twelve weeks. Your surgeon will give you specific guidance based on your job and your healing progress. Driving is usually safe once you can bend your knee enough to work the pedals and are no longer taking strong pain medication.

How long artificial knees last and when revision surgery might be needed

Modern artificial knees typically last 15 to 20 years before the plastic spacer wears down or the metal parts loosen. Some last longer, especially if you are less active or younger at the time of surgery. Younger patients may eventually need a second surgery, called revision surgery, to replace the worn parts.

Revision surgery is more complex than the first replacement because the surgeon must remove the old components and often rebuild bone that has been lost. Recovery is similar to the first surgery but may take slightly longer. The artificial parts used in revision surgery are designed to last another 10 to 15 years. Most people who have a knee replacement never need revision surgery during their lifetime.

Risks and complications

Serious complications are uncommon but possible. Blood clots can form in the leg veins after surgery, though blood thinners and compression stockings lower this risk. Infection at the incision site happens in fewer than 2 out of 100 surgeries. Stiffness — where the knee does not bend as much as expected — can occur if you do not do physical therapy or if scar tissue builds up.

Some people experience persistent pain or swelling that lasts longer than expected. Rarely, the artificial parts can loosen or shift, requiring revision surgery. Nerve or blood vessel injury during surgery is very uncommon. Most complications are treatable, and the vast majority of people who have knee replacement surgery report significant pain relief and improved function.

Frequently Asked Questions

How much pain will I have after knee replacement surgery?

Pain is usually worst in the first week and gradually improves over the next few weeks. Most people describe it as soreness and stiffness rather than sharp pain. Your doctor will prescribe pain medication, and you can also use ice, elevation, and compression to manage discomfort. By four to six weeks, many people need only over-the-counter pain relief.

Can I bend my knee after surgery?

Yes, bending your knee is essential to recovery. Physical therapy focuses on gradually increasing how much you can bend it. Most people can bend their knee 90 degrees (a right angle) within two to three weeks. Full bending — around 110 to 120 degrees — may take several months to achieve.

Will I set off metal detectors with an artificial knee?

Possibly. Some artificial knees contain enough metal to trigger airport security scanners. Your surgeon will give you a card stating you have an implant. Show it to security before screening. You can still go through the metal detector; it may just alarm and require a pat-down search instead.

What activities should I avoid permanently after knee replacement?

High-impact activities like running, jumping, and contact sports are generally not recommended because they can wear out the artificial parts faster. Walking, swimming, cycling, golf, and hiking are usually safe. Your surgeon can advise on specific activities based on your age, health, and the type of implant you received.

How soon can I fly after knee replacement?

Most surgeons clear patients to fly four to six weeks after surgery, once the incision is healed and swelling has decreased. Sitting for long periods can increase clot risk, so get up and walk every hour or two during the flight. Wear your compression stocking and stay hydrated. Check with your surgeon before booking travel.