How a knee replacement operation works

A knee replacement operation removes the damaged surfaces 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, moves the kneecap to the side, and removes the worn cartilage and bone from the ends of your thighbone and shinbone. They then fit the artificial components—called prosthetics—onto the bone surfaces and find them with cement or a special coating that allows bone to grow into them. The kneecap may also be resurfaced or replaced depending on the damage.

The operation typically takes between one and three hours. You will be under general anesthesia (asleep) or regional anesthesia (numb from the waist down), so you will not feel pain during the procedure. A surgical team monitors your heart rate, blood pressure, and oxygen levels throughout.

Key Takeaways

  • The surgeon removes damaged bone and cartilage from your knee joint and replaces them with metal and plastic prosthetics secured with cement or bone-growing coatings.
  • The operation takes one to three hours under anesthesia, and most people stay in the hospital for one to three days afterward.
  • Physical therapy begins within days of surgery and continues for weeks or months to restore strength and movement.
  • Most artificial knees last 15 to 20 years, though this varies based on your age, activity level, and how well you follow recovery instructions.
  • Serious complications like infection or blood clots are uncommon but possible, which is why your surgeon will discuss risks before the operation.

What the surgeon removes and replaces

Your knee joint is where three bones meet: your thighbone (femur), shinbone (tibia), and kneecap (patella). The ends of these bones are covered with cartilage, a smooth tissue that lets them glide against each other. When cartilage wears away—usually from arthritis—bone rubs on bone, causing pain and stiffness.

During the operation, the surgeon removes the damaged cartilage and a thin layer of bone underneath it from the ends of your thighbone and shinbone. They then fit metal caps onto these bone surfaces. A plastic spacer sits between the metal parts to act like new cartilage. The kneecap may be resurfaced with a plastic button or replaced entirely, depending on how much damage it has.

The artificial parts are held in place either with bone cement (a fast-setting adhesive) or with a porous coating that allows your own bone to grow into it over time. Your surgeon will explain which method is right for your situation.

Hospital stay and when ready recovery

Most people stay in the hospital for one to three days after a knee replacement. Before you go home, hospital staff will teach you how to use crutches or a walker, how to climb stairs safely, and what movements to avoid. You will receive pain medication to take at home and instructions on how to care for your incision.

Swelling and bruising are normal and can last for weeks. You may notice fluid draining from the incision for the first few days—this is expected. Your surgeon will tell you when to change the dressing and when the stitches or staples come out, usually 10 to 14 days after surgery.

You will not be able to drive while taking strong pain medication or while your knee is still weak, so arrange for someone to drive you to follow-up appointments. Most people can return to light activities like sitting, eating, and using the bathroom within days, but heavy lifting and strenuous activity must wait several weeks.

Physical therapy and regaining movement

Physical therapy is the most important part of your recovery. It usually starts within 24 hours of surgery, sometimes while you are still in the hospital. A physical therapist will guide you through exercises to reduce swelling, restore the range of motion in your knee, and rebuild the strength in your leg muscles.

In the first weeks, therapy focuses on gentle movement—bending and straightening your knee, walking with support, and reducing swelling with ice and elevation. As weeks pass, exercises become more challenging. You will work on walking without aids, climbing stairs, and eventually returning to activities like swimming or cycling if that is your goal.

Most people attend physical therapy two to three times per week for 6 to 12 weeks, though some continue longer. Your commitment to these exercises directly affects how well your knee works and how quickly you recover. Skipping sessions or not doing exercises at home will slow your progress.

How long the artificial knee lasts

Most artificial knees last 15 to 20 years. This varies based on your age at surgery, how active you are, and how well you follow your surgeon's guidelines. Younger, more active people may wear out their prosthetics faster than older, less active people.

Your surgeon will likely advise you to avoid high-impact activities like running or jumping, as these put extra stress on the artificial joint. Low-impact activities like walking, swimming, and cycling are usually fine and may even be encouraged. Some people do return to running or sports after knee replacement, but this should only happen with your surgeon's approval and after full recovery.

If your artificial knee does wear out or loosen after many years, revision surgery—replacing the prosthetics again—is possible. However, revision surgery is more complex than the first replacement, so protecting your new knee helps you avoid needing it.

Possible complications and risks

Serious complications from knee replacement are uncommon, but they can happen. Infection is one of the most serious risks because an infection in the artificial joint is difficult to treat and may require additional surgery. Your surgical team takes many steps to prevent infection, including using sterile equipment and giving you antibiotics before and after surgery.

Blood clots can form in the veins of your leg after surgery, a condition called deep vein thrombosis (DVT). Your surgeon may prescribe blood-thinning medication or recommend compression stockings to reduce this risk. Signs of a blood clot include sudden swelling, warmth, or redness in your calf.

Other possible complications include stiffness (when your knee does not bend as much as expected), nerve or blood vessel injury, and loosening of the prosthetics over time. Your surgeon will discuss all risks with you before the operation and explain what warning signs to watch for after you go home.

Preparing for surgery and what to expect afterward

Before your operation, your surgeon will order blood tests, an X-ray or MRI of your knee, and possibly an EKG to check your heart. You will meet with an anesthesiologist to discuss any medications you take and any allergies you have. Tell your surgical team about all supplements and over-the-counter medications, as some may need to be stopped before surgery.

The night before surgery, you will be told not to eat or drink anything after midnight. Wear loose, comfortable clothing to the hospital, and leave jewelry and valuables at home. Bring a list of your medications and any medical documents your surgeon has requested.

After surgery, expect pain and swelling for the first few weeks—this is normal and manageable with medication and ice. Most people can walk with crutches or a walker within days and return to driving within four to six weeks. Returning to work depends on your job: desk work may be possible in four to six weeks, while jobs requiring standing or physical labor may take longer.

Frequently Asked Questions

Will I be able to walk normally after knee replacement?

Most people walk normally after full recovery, though this takes time. In the first weeks you will use crutches or a walker. By six to twelve weeks, many people walk without aids. Full recovery and normal walking patterns can take three to six months or longer. Physical therapy is essential to reaching this goal.

Can I have both knees replaced at the same time?

Some surgeons will replace both knees in one operation if you are healthy enough, while others prefer to do them separately a few weeks or months apart. Replacing both at once means one recovery period instead of two, but it is more demanding on your body. Your surgeon will discuss what is safest for you.

What activities should I avoid after knee replacement?

Avoid high-impact activities like running, jumping, and contact sports. Most surgeons recommend low-impact activities like walking, swimming, and cycling. Heavy lifting and kneeling should be limited. Your surgeon will give you specific guidelines based on your age, health, and the type of prosthetic used.

How much pain will I have after surgery?

Pain is common in the first few weeks and is managed with medication, ice, and elevation. Most people describe it as soreness and stiffness rather than sharp pain. Pain should decrease steadily over weeks and months. If pain suddenly increases or does not improve with medication, contact your surgeon.

When can I return to work?

This depends on your job. Desk work may be possible in four to six weeks if you can keep your leg elevated and take breaks to move around. Jobs requiring standing, walking, or physical labor typically take eight to twelve weeks or longer. Your surgeon can provide a work restriction note for your employer.