Knee replacement removes the damaged parts of your knee joint and replaces them with artificial components

A knee replacement is a surgical procedure in which a surgeon removes the worn or damaged surfaces of your knee joint and installs artificial parts made of metal and plastic. The surgery typically takes one to three hours. You receive anesthesia so you do not feel pain during the operation, though you will be unconscious or sedated depending on the type of anesthesia used.

The surgeon makes an incision down the front of your knee, usually four to six inches long. They remove the damaged cartilage and bone from the ends of your thighbone, shinbone, and kneecap. The artificial knee — called a prosthesis — is then secured in place using cement, a special coating that allows bone to grow into it, or both. The incision is closed with stitches or staples.

Most people stay in the hospital for one to three days after surgery. Full recovery typically takes three to six months, though some people continue to improve for up to a year. Physical therapy begins within days of surgery and continues for weeks or months at home.

Key Takeaways

  • Knee replacement surgery removes damaged joint surfaces and replaces them with metal and plastic artificial parts that typically last 15 to 20 years.
  • The procedure takes one to three hours under anesthesia, with a hospital stay of one to three days for most patients.
  • Physical therapy starts within days and continues for months; your activity level during recovery directly affects your final outcome.
  • Common reasons for surgery include severe arthritis, injury, or bone damage that has not improved with other treatments.
  • Risks include infection, blood clots, and stiffness, though serious complications are uncommon in people without other major health problems.

Why surgeons recommend knee replacement

Knee replacement is usually recommended when arthritis or injury has damaged the joint so severely that walking, climbing stairs, or even sitting comfortably causes significant pain. Osteoarthritis — the most common reason — wears away the cartilage that cushions the bones in your knee. Rheumatoid arthritis, post-traumatic arthritis from an old injury, or a fracture that did not heal properly can also lead to replacement.

Before recommending surgery, your doctor will typically try other treatments: physical therapy, weight loss if relevant, anti-inflammatory medications, corticosteroid injections, or injections of hyaluronic acid (a lubricant). If these do not reduce pain enough to let you do the activities that matter to you, surgery becomes an option to discuss.

Age alone is not a barrier. People in their 50s, 60s, 70s, and beyond have successful knee replacements. Your surgeon will assess your overall health, medications, and ability to follow post-surgery instructions rather than focusing on your age.

What the artificial knee is made of

The prosthesis has three main parts: a metal component that replaces the end of your thighbone, a plastic spacer that sits between the thighbone and shinbone, and a metal component that covers the top of your shinbone. Some designs also include a plastic button that replaces the underside of your kneecap.

Modern prostheses are designed to mimic the natural movement of your knee. They are made to last 15 to 20 years in most people, though some last longer. If you are very active or younger, your surgeon may discuss this timeline with you, since you may eventually need a second surgery to replace the worn prosthesis.

The artificial parts are secured using bone cement, a special porous coating that allows your bone to grow into it, or a combination of both methods. Your surgeon will choose the method based on your age, bone quality, and other factors.

The surgery step by step

You arrive at the hospital or surgical center and change into a surgical gown. An anesthesiologist places an IV line and discusses which type of anesthesia you will receive — usually general anesthesia (you are asleep) or regional anesthesia (your leg is numb but you may be sedated). Some surgeons also use a nerve block, which numbs the area around your knee for pain relief after surgery.

Once you are asleep or numb, the surgeon cleans the skin around your knee with an antiseptic solution. They make an incision, usually on the front of your knee, and move the muscles and tendons aside to reach the joint. Using specialized instruments, they remove the damaged cartilage and bone surfaces. They then position the metal components on your thighbone and shinbone and find them in place. The plastic spacer is inserted between them. If your kneecap is damaged, they resurface or replace it as well.

Before closing, the surgeon tests the knee's movement and stability to make sure the prosthesis is positioned correctly. The incision is closed with stitches or staples, and a sterile bandage is applied. You are moved to a recovery room where you wake up gradually.

Pain and swelling after surgery

Pain and swelling are normal in the days and weeks after surgery. You will receive pain medication — usually a combination of over-the-counter pain relievers and prescription medications if needed. Many surgeons recommend ice, elevation, and compression (using an elastic bandage or sleeve) to reduce swelling. You may also wear a continuous passive motion machine, which gently moves your knee while you rest, to prevent stiffness.

Most people describe the pain as manageable rather than severe, especially if they stay on top of pain medication in the first week. Pain typically decreases significantly by week three or four. Swelling can last for months, and some people notice their knee is still slightly swollen a year after surgery.

Walking with crutches or a walker begins within hours or the day after surgery. You will put weight on your leg gradually as tolerated. Your physical therapist will guide you on how much weight is safe and when you can transition to a cane or walk without information.

Physical therapy and recovery timeline

Physical therapy is critical to your outcome. A therapist will visit you in the hospital and teach you exercises to prevent blood clots, reduce swelling, and begin moving your knee. After you go home, you will continue therapy either at a facility or with a home therapist, typically two to three times per week for six to twelve weeks.

Early goals include regaining the ability to straighten your knee fully and bend it to at least 90 degrees. Later goals focus on strength, balance, and returning to activities like walking, climbing stairs, and light exercise. Most people can walk without information by six to eight weeks. Return to driving depends on your pain level, swelling, and ability to control the leg — usually four to six weeks if your right knee was operated on and you do not need pain medication, longer if your left knee was done.

Your effort during therapy directly affects how well your knee works. People who do their exercises consistently regain more motion and strength than those who do not. Some stiffness is common, but aggressive therapy in the first three months can prevent permanent loss of motion.

Risks and complications

Serious complications are uncommon. The most frequent risks are infection (occurring in fewer than 2 out of 100 surgeries), blood clots in the leg or lungs, excessive bleeding, and stiffness. Your surgeon will take steps to prevent each: antibiotics before and after surgery to prevent infection, compression stockings and blood-thinning medication to prevent clots, careful surgical technique to minimize bleeding, and aggressive physical therapy to prevent stiffness.

Less common complications include nerve or blood vessel injury, implant loosening or wear, and persistent pain. Some people experience chronic swelling or a feeling that the knee is not quite right, even though the prosthesis is functioning well. Rarely, the prosthesis can break or dislocate, though this is more likely if you fall or have a high-impact injury years after surgery.

Your overall health affects your risk. People with diabetes, obesity, or poor circulation have higher rates of infection and other complications. Your surgeon will discuss your individual risk before surgery and may recommend steps to reduce it, such as weight loss before the procedure or tighter blood sugar control.

Activity after recovery

Most people can return to low-impact activities like walking, swimming, cycling, and golf within three to six months. High-impact activities — running, jumping, contact sports — are generally not recommended because they can wear out the prosthesis faster and increase the risk of loosening or breaking.

Your surgeon will give you specific guidance based on your prosthesis design and your individual situation. Some people do run or play tennis after knee replacement, but they accept the risk of needing a second surgery sooner. Others prefer to stick with activities that are easier on the joint.

You can expect your artificial knee to feel different from your natural knee. It may not bend quite as far, and you may notice a slight clicking or popping sensation. Most people report that the artificial knee is far more comfortable than their arthritic knee was, even if it is not identical to a healthy natural knee.

Frequently Asked Questions

How long does a knee replacement prosthesis last?

Most prostheses last 15 to 20 years. Some last longer, and some wear out sooner depending on your activity level, body weight, and the quality of your bone. If you need a second surgery to replace a worn prosthesis, it is called a revision. Revision surgery is more complex than the first surgery because the surgeon must remove the old prosthesis and bone that has grown into it.

Can I bend my knee normally after surgery?

Most people regain enough bending to do daily activities like walking, climbing stairs, and sitting in a chair. However, bending is often not quite as full as it was before arthritis developed. Average bending after recovery is around 110 to 120 degrees, compared to 135 degrees or more in a healthy knee. Aggressive physical therapy in the first three months can maximize your bending.

Will I set off metal detectors after knee replacement?

You may. The prosthesis contains metal, and some airport or security metal detectors are sensitive enough to detect it. You can request a pat-down instead of walking through the detector, or you can carry a card from your surgeon stating you have a prosthesis. Not all metal detectors will trigger, so you may pass through without issue at some locations.

What happens if I fall on my new knee?

A fall can damage the prosthesis or the bone around it, though the prosthesis itself is very durable. If you fall, tell your surgeon even if you do not have when ready pain. You may need X-rays to check for fractures or loosening. Preventing falls through balance exercises, proper footwear, and removing tripping hazards at home is important, especially in the first year after surgery.

Can I have another surgery if the prosthesis wears out?

Yes. Revision surgery is possible, though it is more involved than the first surgery because the surgeon must remove the old prosthesis and any bone that has grown into it. Recovery is typically longer, and the outcome is often not quite as good as the first surgery. This is one reason some surgeons recommend waiting until arthritis is severe before doing the first replacement, especially in younger people.