What happens during a knee replacement procedure

A knee replacement takes about one to three hours. Your surgeon removes the damaged cartilage and bone from your knee joint, then fits artificial parts—called prosthetics—in their place. The artificial knee is made of metal and plastic and mimics the way your natural knee bends and straightens.

The surgery happens in a hospital operating room under general anesthesia, which means you are asleep the entire time. A surgical team monitors your heart rate, blood pressure, and oxygen levels throughout. Most people stay in the hospital for one to three days after surgery, though some go home the same day depending on their health and recovery setup at home.

Key Takeaways

  • Your surgeon makes an incision down the front of your knee, usually 8 to 10 inches long, to reach the joint.
  • The damaged bone and cartilage are removed and replaced with metal and plastic prosthetic parts that are cemented or press-fit into place.
  • The entire surgery typically lasts one to three hours, and you will be under general anesthesia the whole time.
  • Recovery in the hospital lasts one to three days, followed by weeks of physical therapy at home or in a clinic to regain strength and movement.
  • Most people can walk with a walker or crutches within days and return to light activities within six weeks, though full recovery takes three to six months.

The surgical approach and incision

Your surgeon begins by making an incision down the front of your knee, typically 8 to 10 inches long. This straight cut runs along the middle of your knee and goes through the skin and the tissue underneath. The surgeon then moves the kneecap to the side to expose the knee joint itself.

Once the joint is visible, the surgeon assesses the damage and confirms which parts need to be replaced. Some knees need only the surfaces that rub together replaced; others require more extensive work. The surgeon's approach depends on the damage pattern and your anatomy, but the front-of-knee incision is standard for most total and partial knee replacements.

Removing damaged bone and cartilage

Your surgeon uses specialized cutting guides and saws to remove the damaged cartilage and a thin layer of bone from the top of your tibia (shin bone) and the bottom of your femur (thighbone). These cuts are precise—usually removing only a quarter inch to half inch of bone—and are angled to match the shape of the prosthetic parts.

The surgeon also cleans out any loose bone fragments or damaged tissue inside the joint. If your knee has significant arthritis, extra bone growths called bone spurs may be removed as well. This preparation step is critical because the prosthetic parts must sit on a clean, properly shaped surface to function correctly and last as long as possible.

Fitting and securing the prosthetic parts

Once the bone surfaces are prepared, your surgeon tests the fit of the prosthetic components—the femoral component (metal piece for the thighbone), the tibial component (metal and plastic piece for the shin bone), and sometimes a plastic button for the kneecap. These test pieces are removed, and the real prosthetics are then secured in place.

Prosthetics are attached using one of two methods: cement or press-fit. Cemented prosthetics are glued to the bone using a special surgical cement that hardens in minutes. Press-fit prosthetics have a rough surface that allows bone to grow into them over time, anchoring them without cement. Your surgeon chooses the method based on your bone quality, age, and activity level. Most surgeons use cement for older patients or those with weaker bone.

After the main prosthetic parts are in place, your surgeon checks the alignment and movement of your new knee. The knee should bend and straighten smoothly, and the alignment should be straight—not tilted inward or outward. If adjustments are needed, the surgeon makes them before closing.

Closing the incision and when ready aftercare

Your surgeon closes the incision with stitches or staples, then covers it with a sterile bandage. You may have a drain—a small tube that removes fluid from the surgical site—left in place for a day or two to prevent swelling. Some surgeons use a technique called a nerve block, which numbs the area around your knee for the first 12 to 24 hours after surgery, reducing pain without heavy pain medication.

In the recovery room, you wake up from anesthesia and are monitored closely. Your leg is usually elevated and may be wrapped in compression bandages to control swelling. You will receive pain medication and blood thinners to prevent clots. Physical therapists often begin gentle movement exercises the same day or the next morning—bending and straightening your knee slightly—to prevent stiffness.

Physical therapy and early recovery

Physical therapy starts in the hospital and continues after you go home. In the first week, the focus is on reducing swelling, protecting the incision, and regaining basic movement. You will learn to walk with a walker or crutches, usually bearing weight on your new knee right away unless your surgeon advises otherwise.

By two to three weeks after surgery, most people can walk without crutches and begin exercises to strengthen the muscles around the knee. Therapy sessions happen two to three times per week for six to twelve weeks. Common exercises include straight-leg raises, heel slides, and stationary cycling. Pain and swelling typically decrease steadily over the first six weeks, though some swelling can persist for three to six months.

Return to activities depends on your progress. Light activities like walking and swimming may resume within four to six weeks. Higher-impact activities like running or jumping are generally not recommended, as they can wear out the prosthetic faster. Most people reach maximum improvement and return to their normal routine within three to six months.

Potential complications during and after surgery

Serious complications during surgery are uncommon but can include blood clots, infection, or damage to blood vessels or nerves. Your surgical team takes steps to prevent these—using compression devices on your legs during surgery, giving you antibiotics, and monitoring carefully. After surgery, you receive blood thinners to reduce clot risk.

Some people experience stiffness if they do not move the knee enough during recovery, or excessive swelling if they overdo activity too soon. Infection of the incision is rare but serious and requires antibiotics or, in severe cases, additional surgery. Most complications are managed successfully when caught early, which is why follow-up appointments with your surgeon are important.

Frequently Asked Questions

How long does the incision take to heal?

The outer skin usually closes within two to three weeks, at which point stitches or staples are removed. However, the deeper tissues and bone continue healing for several months. You should keep the incision clean and dry and watch for signs of infection—increasing redness, warmth, drainage, or fever—and contact your surgeon if you notice them.

Can you feel the artificial knee inside your body?

Most people do not feel the prosthetic itself, but you may notice a slight firmness or awareness of the joint, especially in the first few months. Some people report a clicking or popping sensation when they bend their knee, which is normal and usually decreases over time as swelling goes down and muscles strengthen.

Will the artificial knee set off metal detectors?

Yes, most knee prosthetics contain metal and will trigger metal detectors at airports and security checkpoints. You can request a pat-down instead of walking through the detector, or carry a card from your surgeon documenting the implant. Let security know about the prosthetic before you approach the detector.

How long does a knee replacement last?

Modern prosthetics typically last 15 to 20 years or longer, depending on your activity level and body weight. Heavier people or those who do high-impact activities may experience faster wear. Your surgeon will monitor the knee during follow-up visits and can discuss revision surgery if the prosthetic wears out or fails.

What if you have pain months after surgery?

Some pain and swelling are normal for several months, but increasing pain or new pain should be reported to your surgeon. Pain can signal infection, a problem with how the prosthetic is aligned, or stiffness from not moving enough. Your surgeon can examine the knee and adjust your therapy or medication as needed.