How a Knee Replacement Works

A knee replacement is a surgical procedure in which a surgeon removes damaged bone and cartilage from your knee joint and replaces it with artificial parts made of metal and plastic. The surgeon makes an incision down the front of your knee, typically 8 to 10 inches long, to access the joint. They then remove the damaged surfaces of the thighbone, shinbone, and kneecap, and attach the artificial components using cement or a press-fit method that allows bone to grow into the implant.

The entire surgery usually takes between one and three hours. You will be under general anesthesia or regional anesthesia (numbing from the waist down) so you feel nothing during the procedure. A surgical team including the orthopedic surgeon, anesthesiologist, and nurses will be present throughout.

Key Takeaways

  • The surgeon removes damaged bone and cartilage from your knee and replaces them with metal and plastic implants during a one- to three-hour procedure.
  • You will receive anesthesia so you are unconscious or numb during surgery and will not feel pain.
  • 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 the surgeon's preference.
  • Physical therapy begins within hours or days after surgery and continues for several weeks to help you regain strength and movement in your knee.
  • Full recovery typically takes three to six months, though some people continue improving for up to a year.

What Happens Before Surgery

Before your surgery date, your surgeon will order blood tests, an EKG (heart rhythm test), and possibly X-rays or an MRI to see the exact damage in your knee. You will meet with the anesthesiologist to discuss your medical history and any medications you take. Tell them about all prescriptions, over-the-counter drugs, and supplements, because some must be stopped before surgery.

A few days before surgery, you may be asked to stop taking blood thinners like aspirin or warfarin. You will receive instructions to stop eating and drinking after midnight the night before surgery. Arrange for someone to drive you home, because anesthesia impairs your judgment and reflexes for the rest of the day.

The Surgical Steps

Once you are asleep or numb, the surgeon makes an incision on the front of your knee. They carefully move the kneecap to the side to see the joint surfaces underneath. Using specialized cutting guides, they remove the damaged bone from the end of your thighbone and the top of your shinbone, removing only as much bone as needed to fit the implant.

The surgeon then positions the metal components—usually made of cobalt-chromium or titanium—onto the prepared bone surfaces. A plastic spacer is inserted between the metal parts to create a smooth, gliding surface. If the kneecap is damaged, the surgeon may also resurface it with a plastic button. Once all components are in place and aligned correctly, the surgeon closes the incision with stitches or staples and wraps your knee in a sterile bandage.

Hospital Stay and when ready Recovery

After surgery, you will wake up in a recovery room where nurses monitor your heart rate, blood pressure, and oxygen level. You may feel groggy and have some pain, which the medical team will manage with medication. Most people stay in the hospital for one to three days, though some hospitals now send patients home the same day if they meet certain criteria and have support at home.

While in the hospital, you will begin moving your knee gently, usually within hours of surgery. A physical therapist will show you how to do straightforward exercises and use crutches or a walker. You will also receive blood clot prevention medication, because surgery increases the risk of clots forming in your legs. Before you leave, the hospital will give you written instructions for wound care, medication, and when to call your surgeon.

Physical Therapy and Regaining Movement

Physical therapy is critical to your recovery and begins when ready after surgery. In the first few weeks, your therapist focuses on reducing swelling, protecting the incision, and gently bending and straightening your knee. You will do exercises at home between therapy sessions, typically three to five times per week for the first month.

By four to six weeks after surgery, most people can walk without crutches and begin strengthening exercises. By three months, many return to light activities like walking, swimming, or stationary cycling. Your therapist will gradually increase the intensity of exercises to rebuild the muscles around your knee, which weaken during surgery and recovery.

Timeline for Returning to Normal Activities

Most people can return to light desk work within two to four weeks if they keep their leg elevated and take pain medication as needed. Driving is usually safe four to six weeks after surgery, once you can bend your knee enough to sit comfortably and your reflexes are no longer affected by pain medication. Return to more demanding work or hobbies depends on the activity—some people resume golf or hiking by three to four months, while others take six months or longer.

Full recovery typically takes three to six months, though some people continue to see improvement in strength and movement for up to a year. Your surgeon will tell you which activities are safe at each stage. Most people who have knee replacement can return to moderate activities like walking, swimming, and light sports, though high-impact activities like running or jumping are usually not recommended.

Possible Complications and What to Watch For

Serious complications are uncommon, but they can include blood clots in the leg, infection, or damage to blood vessels or nerves. Signs of a blood clot include sudden swelling, warmth, or redness in your calf. Signs of infection include fever, increasing redness or warmth around the incision, or drainage that smells bad or looks like pus. Contact your surgeon when ready if you notice any of these.

Less serious but common issues include stiffness, swelling that comes and goes, and mild pain with activity. These usually improve with continued physical therapy and time. Some people experience persistent swelling or occasional clicking or popping in the knee, which is often normal and does not mean something is wrong with the implant.

Frequently Asked Questions

How long does a knee replacement implant last?

Most modern knee implants last 15 to 20 years or longer. Some people never need a second surgery, while others may need a revision procedure later in life if the implant wears out or becomes loose. Your surgeon can discuss the expected lifespan of your specific implant.

Will I set off metal detectors after knee replacement?

You may trigger metal detectors at airports or security checkpoints because the implant contains metal. Carry your surgical implant card, which your surgeon will give you, to show security personnel. You can usually pass through with the card, though you may be patted down or scanned with a handheld detector.

Can I play sports after knee replacement?

Low-impact activities like walking, swimming, golf, and cycling are generally safe after full recovery. High-impact sports like running, basketball, or tennis are usually not recommended because they can wear out the implant faster. Ask your surgeon which specific activities are safe for your situation.

What if I need surgery on my other knee?

Many people have both knees replaced, either at the same time or in separate surgeries weeks or months apart. Your surgeon will discuss the pros and cons of each approach based on your age, health, and recovery ability.

How much pain should I expect after surgery?

Pain is normal for the first few weeks and is usually managed well with prescribed pain medication. Most people describe it as soreness or aching rather than sharp pain. Pain should gradually decrease over weeks and months. If pain suddenly increases or does not improve with medication, contact your surgeon.