The surgeon removes the damaged bone and cartilage, then anchors a metal and plastic implant to your thighbone and shinbone
Knee replacement surgery takes about one to two hours. Your 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, then use a saw to remove the damaged ends of your thighbone and shinbone. They also trim away any bone spurs and damaged cartilage.
Once the damaged surfaces are gone, your surgeon tests the fit of the metal implant pieces — one shaped to cap the end of your thighbone, one to cover the top of your shinbone. These metal parts are cemented or press-fit into place. A plastic spacer sits between them to act as your new cartilage. Your surgeon may also resurface the back of your kneecap with a plastic button, depending on its condition.
After the implant is find, your surgeon closes the incision with stitches or staples, wraps your knee, and you move to recovery. You will be awake during parts of the procedure if you receive regional anesthesia (numbing from the waist down), or asleep if you receive general anesthesia.
Key Takeaways
- The surgeon makes one incision down the front of your knee and removes the damaged bone and cartilage from both the thighbone and shinbone.
- Metal implants are cemented or press-fit to the cut bone surfaces, with a plastic spacer between them to replace your worn cartilage.
- The entire procedure takes one to two hours, and you will receive either regional or general anesthesia so you feel no pain.
- Your surgeon may also resurface the back of your kneecap if it is damaged, though not all knee replacements include this step.
- Most people go home the same day or stay one night in the hospital, then begin physical therapy within days.
What happens before the surgeon makes the incision
Before surgery begins, the anesthesiologist will place an IV line and give you medication to relax. If you are having regional anesthesia, they will inject numbing medication around the nerves that supply your knee — you will be awake but feel nothing below the waist. If you are having general anesthesia, you will be given medication through the IV and fall asleep; a breathing tube may be placed to help you breathe during the procedure.
Once you are numb or asleep, a nurse will clean your knee with an antiseptic solution and drape it with sterile sheets. Your surgeon will mark the incision line. Some surgeons use a computer-assisted navigation system or robotic tools to help position the implant with precision, though this is not standard at all hospitals.
How the surgeon removes the damaged bone
Your surgeon makes a single incision, usually 8 to 10 inches long, down the front of your knee. They cut through the skin, fat, and the tissue capsule that surrounds your joint. The kneecap is moved to the side — not removed — so your surgeon can see the joint surfaces underneath.
Using a specialized saw, your surgeon removes a thin layer of bone from the end of your thighbone and the top of your shinbone. The amount removed is small and carefully measured to match the thickness of the metal implant that will replace it. Your surgeon also removes any bone spurs and any cartilage that is worn away or damaged.
If your kneecap is severely damaged, your surgeon will also resurface its back surface by removing a thin layer of bone and cementing a plastic button in place. Not all knee replacements include this step — your surgeon will decide based on the condition of your kneecap during surgery.
How the implant is positioned and secured
Your surgeon will test-fit the metal implant pieces to make sure they sit properly on the bone and that your knee bends and straightens smoothly. The implant for your thighbone is shaped like an upside-down U; the implant for your shinbone is a flat platform. Once the fit is correct, your surgeon cements them into place using a special bone cement, or press-fits them so they grip the bone without cement. Both methods are durable — your surgeon will choose based on your age, bone quality, and other factors.
A plastic spacer, usually made of ultra-high-molecular-weight polyethylene, is inserted between the metal pieces. This plastic acts as your new cartilage and allows your knee to bend and straighten. Your surgeon will test the knee again to make sure it moves smoothly and that your leg is properly aligned.
Closing the incision and moving to recovery
Once your surgeon is satisfied with the implant position and knee motion, they will close the incision. The tissue capsule around your joint is stitched closed, then the skin is closed with stitches or staples. Your knee is wrapped with a sterile bandage and often placed in a compression sleeve or brace to reduce swelling.
You will be moved to the recovery room, where nurses will monitor your heart rate, blood pressure, and oxygen level as the anesthesia wears off. You may feel groggy or nauseous — this is normal and usually passes within an hour. Pain medication will be given as needed. Most people are discharged the same day or stay one night in the hospital.
What to expect in the first few weeks after surgery
Your knee will be swollen, stiff, and painful for the first few weeks. You will wear a compression sleeve and ice your knee several times a day to reduce swelling. Pain medication will be prescribed, usually a combination of over-the-counter and prescription drugs.
Physical therapy begins within days of surgery — sometimes even the day of surgery. A therapist will teach you exercises to restore your knee's range of motion and strengthen the muscles around it. You will also learn how to walk with crutches or a walker. Most people can put weight on their leg within a few days, though they may need crutches for two to four weeks.
Stitches or staples are removed about two weeks after surgery. Swelling and stiffness gradually improve over three to six months, though some people continue to improve for up to a year. Most people can return to light activities like walking and swimming within six to twelve weeks.
How long the implant lasts and what can go wrong
Modern knee implants are designed to last 15 to 20 years or longer. Over time, the plastic spacer can wear down, and the implant can loosen. If this happens, you may need a second surgery to replace the worn implant — this is called a revision surgery and is more complex than the first replacement.
Infection is rare but serious and can occur in the weeks or months after surgery. Signs include fever, increasing pain, redness, warmth, or drainage from the incision. Blood clots can form in your leg veins after surgery; your surgeon may prescribe blood-thinning medication to reduce this risk. Other complications include nerve or blood vessel injury, implant loosening, and stiffness if you do not do physical therapy.
Most people do not experience serious complications. Talking with your surgeon before surgery about your medical history, medications, and any concerns will help reduce your risk.
Frequently Asked Questions
Will I be awake during knee replacement surgery?
You may be awake or asleep depending on the type of anesthesia you receive. Regional anesthesia numbs you from the waist down so you are awake but feel no pain. General anesthesia puts you to sleep. Your anesthesiologist will discuss which option is best for you based on your health and preferences.
How much of my knee is replaced?
Only the damaged surfaces of your thighbone and shinbone are replaced with metal implants. The bones themselves are not removed — your surgeon removes a thin layer from the ends and caps them with metal. Your ligaments, tendons, and most of your bone remain unchanged. This is why it is called a partial or total replacement depending on how much of the joint is damaged.
Can I feel the implant moving inside my knee?
No. Once healed, you should not feel the implant. Some people report a clicking or popping sensation when they bend their knee, which is normal and usually fades over time. The plastic spacer and metal surfaces are designed to move smoothly together, similar to your natural knee joint.
What activities can I do after knee replacement?
Most people can walk, swim, bike, and do low-impact exercise. High-impact activities like running, jumping, or contact sports are generally not recommended because they can wear out the implant faster. Your surgeon and physical therapist will give you specific guidelines based on your recovery and the type of implant you received.
How do I know if my implant is failing?
Signs of implant problems include increasing pain, swelling that does not improve, a feeling that your knee is giving way, or a change in how your knee feels or moves. If you notice any of these, contact your surgeon. Regular follow-up appointments help catch problems early, and X-rays can show if the implant is loosening or wearing.