The basic steps of knee replacement surgery

A knee replacement removes the damaged parts 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 reach the joint. They then remove the damaged cartilage and bone from the ends of your thighbone and shinbone, and sometimes from the kneecap.

Once the damaged surfaces are removed, the surgeon fits the artificial parts — called prosthetics — onto the prepared bone. The thighbone gets a metal cap, the shinbone gets a metal tray with a plastic spacer, and sometimes the kneecap gets a plastic button. The surgeon tests the fit and alignment before closing the incision with stitches or staples. The whole procedure typically takes 1 to 2 hours.

Key Takeaways

  • The surgeon removes damaged cartilage and bone from your thighbone, shinbone, and sometimes kneecap, then attaches metal and plastic prosthetics to the remaining bone.
  • The incision is made down the front of the knee and is usually 8 to 10 inches long; the surgery takes 1 to 2 hours under general or regional anesthesia.
  • Most people stay in the hospital for 1 to 3 days, though some go home the same day depending on their health and the surgeon's approach.
  • Physical therapy begins within hours or days after surgery and continues for weeks or months to restore strength and movement.
  • Full recovery typically takes 3 to 6 months, though some improvement continues for up to a year.

What happens before you go into the operating room

Before surgery, your surgical team will review your medical history, current medications, and any allergies. You will have blood work and imaging tests done in the weeks before your surgery date. The night before surgery, you will be told not to eat or drink anything after midnight, because anesthesia works best on an empty stomach.

On the day of surgery, you will change into a hospital gown and meet with the anesthesiologist, who will discuss which type of anesthesia you will receive — usually general anesthesia (you are asleep) or regional anesthesia (your lower body is numb but you are awake). A nurse will place an IV line in your arm for fluids and medications. You will then be taken to the operating room, where the surgical team will position you on the operating table and prepare your knee with antiseptic solution.

How the surgeon positions and prepares the joint

Once you are under anesthesia, the surgeon makes a single incision down the front of your knee. This approach, called the medial parapatellar approach, is the most common. The surgeon carefully moves the tissues aside to expose the knee joint itself.

The surgeon then uses specialized cutting guides and saws to remove the damaged cartilage and bone from the end of your thighbone and the top of your shinbone. The amount removed is carefully measured so that the artificial parts will fit properly and your knee will be aligned correctly. If your kneecap is also damaged, the surgeon may resurface it by removing the damaged cartilage and attaching a plastic button.

Installing the prosthetic parts and testing alignment

After the bone surfaces are prepared, the surgeon cements or presses the metal components onto the bone. The thighbone receives a metal femoral component, the shinbone receives a metal tibial tray, and a plastic insert (called a polyethylene spacer) sits between them to allow smooth movement. Some surgeons use cementless prosthetics that rely on a textured surface to allow bone to grow into them over time; others use cemented prosthetics that are bonded to the bone when ready.

Before closing, the surgeon tests the knee's movement and alignment by bending and straightening it. They check that the prosthetics are stable and that your leg is straight. If the alignment is off, they adjust the components. Once everything is correct, they close the incision with stitches or staples and explore a sterile dressing.

Hospital stay and the first days after surgery

Most people stay in the hospital for 1 to 3 days after knee replacement, though some hospitals now send patients home the same day if they meet certain criteria — good overall health, a strong support system at home, and access to outpatient physical therapy. You will wake up in a recovery room where nurses monitor your heart rate, blood pressure, and oxygen level. You may feel groggy, and your knee will be swollen and painful.

Pain management begins when ready. You will receive pain medication through your IV or by mouth, and you may have a nerve block — an injection near your knee that numbs the area for several hours. Many hospitals use ice machines and compression wraps to reduce swelling. A nurse will help you move your leg and do gentle exercises within hours of surgery, even though it will be uncomfortable. This early movement prevents blood clots and stiffness.

Physical therapy and regaining movement

Physical therapy is a critical part of recovery and begins in the hospital. A therapist will help you bend and straighten your knee, teach you how to walk with crutches or a walker, and show you exercises to do at home. In the first week, the goal is to bend your knee to about 90 degrees and straighten it fully. You will also learn how to manage swelling with ice and elevation.

After you leave the hospital, you will continue outpatient physical therapy 2 to 3 times per week for 4 to 6 weeks, and sometimes longer. The therapist will gradually increase the range of motion in your knee, build strength in your thigh and calf muscles, and help you walk normally again. By 6 weeks, most people can walk without a walker or crutches. By 3 months, many can return to light activities like swimming or stationary cycling. Full recovery — including the ability to do stairs, light hiking, or golf — typically takes 3 to 6 months.

What to expect during the first weeks at home

At home, you will need to keep your knee elevated and iced to manage swelling. You will take pain medication as prescribed, usually for the first 2 to 4 weeks. Your surgeon will give you specific instructions about when you can shower, drive, or return to work — most people cannot drive while taking strong pain medication or while their knee is still very swollen.

You may notice fluid draining from the incision or bruising around your knee; both are normal. However, contact your surgeon if you develop fever, increasing redness or warmth around the incision, or sudden increased swelling or pain. You will have a follow-up appointment with your surgeon 2 to 6 weeks after surgery to check your healing and discuss your progress in physical therapy.

Frequently Asked Questions

How long does the incision take to heal?

The skin usually closes within 2 to 3 weeks, and stitches or staples are removed around that time. However, the deeper tissues and bone continue to heal for several months. You should avoid soaking the incision in water until it is fully closed and your surgeon says it is safe.

Will I need a blood transfusion during knee replacement?

Most people do not need a transfusion. However, if you lose a significant amount of blood during surgery, your surgeon may recommend one. Some surgeons use techniques like cell salvage — collecting and reusing your own blood — to reduce the need for donor blood.

Can I get an infection after knee replacement?

Infection is rare but serious. It occurs in fewer than 2 out of 100 knee replacements. Signs include fever, increasing redness or warmth around the incision, or drainage that smells bad. Contact your surgeon when ready if you notice these signs. You will receive antibiotics before surgery to reduce infection risk.

What happens if my prosthetic wears out?

Prosthetics can last 15 to 20 years or longer, depending on your activity level and the type used. If it does wear out, you may need a second surgery called a revision replacement. This is more complex than the first surgery because the surgeon must remove the old prosthetic and prepare the bone again.

When can I return to normal activities like exercise?

Most people can walk and do light activities like swimming by 3 months. Higher-impact activities like running or jumping are generally not recommended, as they can wear out the prosthetic faster. Your surgeon and physical therapist can advise you on what activities are safe for your specific situation.