What happens during a knee replacement procedure

A knee replacement removes the damaged surfaces of your knee joint and replaces them with artificial parts made of metal and plastic. The surgeon makes an incision down the front of your knee, usually 8 to 10 inches long, to access the joint. They then remove the damaged cartilage and bone from the ends of your thighbone, shinbone, and kneecap, shaping the remaining bone to fit the artificial components.

The artificial knee—called a prosthesis—consists of a metal stem and tray that attach to your thighbone and shinbone, plus a plastic spacer between them that mimics cartilage. Some surgeries also replace the kneecap surface with a plastic button. The surgeon tests the fit and range of motion before closing the incision with stitches or staples. The entire procedure typically takes 1 to 3 hours.

Key Takeaways

  • Knee replacement removes damaged bone and cartilage and replaces them with metal and plastic parts that allow the joint to move smoothly again.
  • The surgery takes 1 to 3 hours and requires a hospital stay of 1 to 3 days, though some patients go home the same day.
  • Physical therapy starts within 24 hours after surgery and continues for several weeks to restore strength and range of motion.
  • Most artificial knees last 15 to 20 years, after which revision surgery may become necessary.
  • Pain relief and improved mobility usually become noticeable within 6 to 12 weeks, with continued improvement for up to a year.

Why your doctor might recommend knee replacement

Knee replacement is typically recommended when arthritis or injury has damaged the joint so severely that other treatments no longer work. Osteoarthritis—the most common reason—wears away the cartilage that cushions your knee, causing bone-on-bone contact, pain, and stiffness. Rheumatoid arthritis, post-traumatic arthritis from an old injury, or a fracture that cannot be repaired may also lead to replacement.

Your doctor will usually try other options first: physical therapy, weight management, anti-inflammatory medications, corticosteroid injections, or a procedure called viscosupplementation (injecting lubricating fluid into the joint). Knee replacement becomes an option when these approaches no longer control your pain or restore enough function for daily activities. Most people who have the surgery are over 50, though age alone does not determine whether you are a candidate.

What happens before surgery

Before your surgery date, you will have blood tests, X-rays, and possibly an MRI to give your surgical team a detailed picture of your knee. You may also have an EKG (heart test) or chest X-ray if you have heart or lung conditions. Your surgeon will review your medications with you—some, like blood thinners, may need to stop a few days before surgery to reduce bleeding risk.

You will meet with an anesthesiologist who will discuss which type of anesthesia you will receive: general anesthesia (you are asleep), regional anesthesia (your leg is numb but you are awake), or a combination. The night before surgery, you will be told to stop eating and drinking at a specific time. On surgery day, arrive early to change into a hospital gown and have an IV placed in your arm.

The first 24 to 48 hours after surgery

You will wake up in a recovery room where nurses monitor your heart rate, blood pressure, and oxygen level. Your leg will be wrapped in a compression bandage to reduce swelling, and you may have a drain tube that removes excess fluid—this is usually removed within 24 hours. Pain medication is given through your IV or as pills, and you will receive antibiotics to prevent infection.

Physical therapy begins almost when ready, often within 24 hours. A therapist will help you move your knee gently, straighten your leg, and begin walking with crutches or a walker. This early movement prevents blood clots and stiffness. Most patients stay in the hospital for 1 to 3 days, though some go home the same day if they have good support at home and can manage stairs and basic self-care.

Physical therapy and recovery at home

Once home, you will continue physical therapy 2 to 3 times per week for 6 to 12 weeks. A therapist will guide you through exercises to restore your knee's range of motion and rebuild the muscles around it. You will practice bending and straightening your knee, walking distances that gradually increase, and using stairs. Ice and elevation help control swelling, especially in the first 2 to 3 weeks.

Pain and swelling typically peak around day 3 to 5 after surgery, then gradually improve. Most people can walk without crutches within 3 to 6 weeks and return to light activities like driving within 4 to 6 weeks (once you stop taking narcotic pain medication). Full recovery—when strength and flexibility are restored—usually takes 3 to 6 months, though some improvement continues for up to a year.

What your artificial knee can and cannot do

An artificial knee allows you to walk, climb stairs, swim, golf, and do most daily activities. It bends to about 110 to 120 degrees, which is enough for normal walking and sitting. However, it does not bend as far as a natural knee, so activities like kneeling or sitting cross-legged may feel uncomfortable or impossible.

High-impact activities—running, jumping, contact sports—are generally not recommended because they can loosen the artificial components faster. Low-impact exercise like walking, cycling, swimming, and water aerobics is encouraged. Your surgeon will give you specific guidelines based on your individual situation. Most artificial knees last 15 to 20 years before revision surgery becomes necessary, though some last longer.

Complications and what to watch for

Serious complications are uncommon but possible. Blood clots can form in the leg veins after surgery—signs include calf swelling, warmth, or pain. Infection can occur at the incision site or deeper in the joint; fever, increasing redness, warmth, or drainage are warning signs. Stiffness sometimes develops if physical therapy is delayed or not done consistently. Rarely, the artificial components can loosen or wear out faster than expected.

Contact your surgeon when ready if you develop fever over 101°F, increasing pain not controlled by medication, severe swelling, redness or drainage from the incision, calf pain or swelling, chest pain, or shortness of breath. Most people recover without major problems, but knowing these signs helps you catch issues early.

Frequently Asked Questions

How long does it take to feel normal after knee replacement?

Most people notice significant pain relief and improved mobility within 6 to 12 weeks. However, full recovery—when strength and flexibility are back to normal—takes 3 to 6 months. Some improvement continues for up to a year as swelling decreases and muscles rebuild.

Can I kneel after knee replacement?

Kneeling is difficult and often uncomfortable after knee replacement because the artificial joint does not bend as far as a natural knee, and the incision area may be sensitive. Some people learn to kneel on a padded surface over time, but it is not recommended as a regular activity.

Will I need a second surgery on the same knee?

Most artificial knees last 15 to 20 years. After that time, revision surgery—replacing the worn components—may become necessary. However, many people never need revision surgery, and advances in materials mean newer implants may last even longer.

Can I fly after knee replacement?

You can usually fly 4 to 6 weeks after surgery, once you can walk without crutches and your surgeon clears you. Sitting for long periods increases blood clot risk, so get up and walk every 2 hours, wear compression socks, and stay hydrated. Notify airport security that you have a metal implant.

What if I gain weight after knee replacement?

Extra weight puts more stress on your artificial knee and can shorten its lifespan. Maintaining a healthy weight through diet and low-impact exercise like swimming or cycling helps protect your implant and reduces pain and swelling.