Knee replacement surgery removes a damaged knee joint and replaces it with an artificial one

Knee replacement, also called knee arthroplasty, is a surgical procedure where a surgeon removes the worn or damaged surfaces of your knee joint and installs artificial components made of metal and plastic. The surgery typically takes one to three hours. You will be under general anesthesia (fully asleep) or regional anesthesia (numb from the waist down), so you will not feel pain during the procedure.

The artificial knee, called a prosthesis, mimics the shape and movement of a healthy knee. It has three main parts: a metal component that replaces the thighbone surface, a metal or plastic component that replaces the shinbone surface, and a plastic spacer between them that acts like cartilage. Most prostheses last 15 to 20 years before they may need revision (replacement of the replacement).

Surgeons perform knee replacement when arthritis, injury, or other damage makes the joint painful and limits movement despite other treatments like physical therapy, injections, or anti-inflammatory medication. The decision to have surgery is yours and your doctor's together—there is no single age or damage level that automatically means you need it.

Key Takeaways

  • Knee replacement removes damaged joint surfaces and installs artificial metal and plastic components that typically last 15 to 20 years.
  • The surgery takes one to three hours under anesthesia and is performed when arthritis or injury causes pain that does not improve with other treatments.
  • Recovery involves hospital or outpatient discharge within one to two days, followed by physical therapy that usually lasts several weeks to months.
  • Most people regain the ability to walk, climb stairs, and do daily activities, though high-impact sports are usually not recommended.
  • Infection, blood clots, and stiffness are possible complications, but serious problems occur in a small percentage of cases.

How the surgeon performs the procedure

The surgeon makes an incision down the front of your knee, usually 8 to 10 inches long. They then move the kneecap aside to access the joint underneath. Using specialized cutting guides and instruments, they remove the damaged cartilage and bone from the end of your thighbone and the top of your shinbone, creating flat surfaces.

Once the bone surfaces are prepared, the surgeon cements or press-fits the metal components onto the bone. They then insert the plastic spacer between the metal parts. Some surgeons use a technique called computer-assisted navigation or robotic information to position the components with high precision, though traditional manual techniques are also effective. The surgeon tests the knee's movement and alignment before closing the incision with stitches or staples.

What to expect when ready after surgery

You will wake up in a recovery room where nurses monitor your heart rate, blood pressure, and oxygen level. Your knee will be wrapped in a compression bandage and possibly in a cooling device to reduce swelling. You will have a catheter (a tube) to drain fluid from the surgical site for the first day or two, and you may have a drain tube as well.

Pain is normal and expected. You will receive pain medication through an IV or by mouth. Most hospitals use a multimodal approach, meaning they combine different types of pain relief to keep you comfortable while minimizing side effects. You will also receive blood-thinning medication to reduce the risk of clots in your legs.

Physical therapists will begin working with you within hours of surgery, helping you move your knee gently and teaching you to walk with crutches or a walker. This early movement is crucial—it reduces stiffness and speeds recovery. Most people go home within one to two days, though some stay longer depending on their health and living situation.

Recovery timeline and physical therapy

The first two weeks at home focus on managing pain and swelling while gradually increasing movement. You will ice your knee several times a day, keep it elevated, and take prescribed pain medication as needed. You will use crutches or a walker and attend physical therapy two to three times per week.

By four to six weeks, most people can walk without crutches and begin gentle strengthening exercises. Swelling usually peaks around two weeks and then gradually decreases over several months. By three months, many people can return to light activities like walking, swimming, or stationary cycling. Full recovery—when strength and flexibility are maximized—typically takes six to twelve months.

Physical therapy is essential and not optional. The exercises you do determine how much movement and strength you regain. People who skip or rush through therapy often end up with a stiff knee or weakness that limits their activities. Your therapist will give you exercises to do at home on days you do not have scheduled sessions.

Possible complications and risks

Infection is the most serious complication, occurring in fewer than 2 percent of cases. Signs include fever, increasing redness or warmth around the incision, or drainage from the wound. Infection can usually be treated with antibiotics if caught early, but severe infections may require additional surgery.

Blood clots can form in the leg veins after surgery. This is why you receive blood-thinning medication and are encouraged to move your legs frequently. Symptoms include calf swelling, warmth, or pain. Tell your doctor when ready if you notice these signs.

Stiffness can develop if you do not move the knee enough during recovery. This is why physical therapy starts so soon after surgery. Other less common complications include nerve or blood vessel injury, persistent pain, or the prosthesis becoming loose over time. Your surgeon will discuss your individual risk factors before the procedure.

What activities you can and cannot do after recovery

Once fully healed, most people can walk, climb stairs, swim, cycle, golf, and do yard work without limitation. Many return to work within four to six weeks if their job does not require heavy lifting or prolonged standing. You can drive once you are off narcotic pain medication and can move your knee enough to operate the pedals—usually four to six weeks.

High-impact activities like running, jumping, or contact sports are generally not recommended because they can wear out the prosthesis faster and increase the risk of loosening. Low-impact activities are gentler on the artificial joint and tend to extend its lifespan. Your surgeon and physical therapist can advise you on which specific activities are safe for your situation.

Preparing for surgery and what to bring

Before surgery, your doctor will order blood tests, an EKG (heart tracing), and possibly imaging to assess your overall health. You will meet with the anesthesiologist to discuss your medical history and any medications you take. Stop eating and drinking at midnight the night before surgery, as instructed by your hospital.

Arrange for someone to drive you home and stay with you for at least the first few days. You will not be able to drive yourself, and you will need help with basic tasks like bathing and preparing meals. If you live alone, discuss this with your surgeon—some people arrange temporary home care or stay with family.

Bring your insurance card, photo ID, and a list of all medications and supplements you take. Wear loose, comfortable clothing that is straightforward to remove. Leave jewelry, watches, and valuables at home. Your hospital will provide specific instructions about what to bring and what to avoid.

Frequently Asked Questions

How long does a knee replacement last?

Most modern prostheses last 15 to 20 years. Some last longer, and some wear out sooner depending on your activity level, weight, and how well you follow physical therapy. If your prosthesis loosens or wears out, revision surgery can replace it, though revision surgery is more complex than the first replacement.

Will I set off metal detectors after knee replacement?

You may trigger some metal detectors because the prosthesis contains metal. Your surgeon will give you a card stating you have a knee replacement. Show this at airport security or other checkpoints. Metal detectors at stores rarely cause problems because they are less sensitive.

Can I have an MRI after knee replacement?

Most modern knee prostheses are MRI-safe, but some older ones are not. Tell your doctor and the MRI facility that you have a knee replacement. They will verify that your specific prosthesis is safe before proceeding. If it is not safe, other imaging options like CT scans may be used instead.

What if I gain weight after surgery?

Extra weight puts more stress on the artificial knee and can shorten its lifespan. Maintaining a healthy weight helps the prosthesis last longer and reduces pain and swelling. Your doctor or a nutritionist can help you with weight management after recovery is complete.

Do I need antibiotics before dental work after knee replacement?

Current guidelines do not recommend routine antibiotics before dental work for people with knee replacements. However, if you have signs of infection or your immune system is compromised, your doctor may recommend them. Ask your surgeon and dentist about your specific situation.