The surgeon removes damaged cartilage and bone, then attaches artificial joint parts

Knee replacement surgery takes about one to three hours. The surgeon makes an incision down the front of your knee, usually 8 to 10 inches long. They remove the damaged cartilage and bone from the ends of your thighbone, shinbone, and kneecap. Then they attach metal and plastic artificial joint parts—called prosthetics—to the healthy bone that remains. The plastic spacer between the metal parts mimics the cartilage your knee lost.

You will be asleep under general anesthesia during the entire procedure. A regional block—numbing medication around the nerves in your leg—is often added so you feel less pain when you wake up. The surgeon works with an orthopedic team that includes a surgical nurse and an anesthesiologist who monitors your heart rate, blood pressure, and oxygen level throughout.

Key Takeaways

  • The surgeon removes damaged bone and cartilage from your thighbone, shinbone, and kneecap, then attaches metal and plastic prosthetics to the healthy bone underneath.
  • The incision is usually 8 to 10 inches long and runs down the front of your knee; the surgeon may use a tourniquet to reduce bleeding during the procedure.
  • The surgery takes one to three hours, and you will be asleep under general anesthesia plus a regional nerve block for pain control.
  • After the prosthetics are attached, the surgeon closes the incision with stitches or staples and wraps your knee in a compression bandage to control swelling.

How the surgeon positions your leg and controls bleeding

Before the incision, your leg is positioned on the operating table so the surgeon has clear access to the front of your knee. Your leg may be elevated or supported with a pillow under the ankle. Many surgeons use a tourniquet—an inflated cuff around your upper thigh—to squeeze off blood flow to the knee. This keeps the surgical field dry so the surgeon can see exactly what they are removing and where to attach the new parts. The tourniquet is released once the prosthetics are in place.

The surgeon makes the incision through skin, fat, and the tissue layer beneath. They then separate the muscles and tendons on either side of the knee without cutting them—this is called a quadriceps-sparing approach or a medial parapatellar approach, depending on the surgeon's technique. Both methods preserve the strength of the muscles around your knee, which matters for your recovery later.

Removing damaged bone and cartilage

Once the surgeon has access to the joint, they remove the cartilage and bone that arthritis has worn away. They use special cutting guides and saws to remove a precise thickness of bone from the end of your thighbone and the top of your shinbone. The amount removed is usually less than a quarter inch, but it is enough to create a flat surface where the metal prosthetics will sit. The surgeon also removes any bone spurs or loose cartilage fragments.

The kneecap is handled separately. The surgeon removes the damaged cartilage from the back of the kneecap and shapes the bone into a smooth dome. Some surgeons resurface the kneecap with a plastic button; others leave it as is, depending on the damage and the type of prosthetic being used. This decision is made before surgery based on X-rays and the surgeon's assessment.

Attaching the metal and plastic prosthetics

The prosthetic parts come in different sizes. The surgeon selects the right size by testing trial pieces on your bone to may support a snug fit. Once the correct size is chosen, the metal components are cemented or press-fit onto the bone. Cemented prosthetics use a special bone cement that hardens in minutes; press-fit prosthetics rely on a tight mechanical fit and may have a porous surface that bone grows into over time.

The thighbone prosthetic is a metal cap that covers the end of your thighbone. The shinbone prosthetic is a metal tray that sits on top of your shinbone. A plastic spacer—usually made of ultra-high-molecular-weight polyethylene—is placed between them. This plastic acts like the cartilage your knee no longer has, allowing the metal parts to glide smoothly. The surgeon tests the fit by moving your knee through its range of motion to make sure the parts are aligned and stable.

Closing the incision and wrapping the knee

Once the surgeon is satisfied with the fit and alignment, they release the tourniquet and allow blood to flow back to your leg. Any bleeding vessels are sealed with cautery or tied off. The surgeon then closes the incision in layers. The tissue beneath the skin is closed with absorbable stitches that dissolve on their own. The skin is closed with stitches, staples, or a combination of both, depending on the surgeon's preference.

Your knee is then wrapped in a compression bandage or elastic wrap to control swelling. Some surgeons place a drain—a small tube—under the bandage to collect excess fluid that builds up after surgery. This drain is usually removed within a day or two. You are moved to the recovery room while you wake up from anesthesia, and your vital signs are monitored closely.

Common variations in surgical technique

Not all knee replacements are done the same way. Some surgeons use a minimally invasive approach with a shorter incision, usually 4 to 6 inches, though the prosthetics are the same size. Others use a traditional longer incision. Computer-assisted navigation is sometimes used to help the surgeon position the prosthetics with greater precision. Robotic-assisted surgery is also available at some hospitals, where a robot helps guide the surgeon's instruments, though the surgeon remains in control throughout.

The choice of prosthetic design also varies. Some prosthetics are designed to move like a normal knee; others are more constrained to provide extra stability if your ligaments are weak. Your surgeon will discuss which approach and prosthetic type are best for your knee based on your age, activity level, and the extent of damage.

What to expect in the recovery room

After surgery, you will spend one to two hours in the recovery room as the anesthesia wears off. A nurse will check your blood pressure, heart rate, and oxygen level regularly. Your leg will be elevated on pillows to reduce swelling. Ice packs may be applied to your knee. You will likely feel drowsy and may have some pain, which is managed with medication given through an IV or by mouth.

Most people go home the same day or stay overnight, depending on how they are recovering and their overall health. Before you leave, you will receive instructions on how to care for your incision, manage pain, use ice and elevation, and begin gentle movement. Physical therapy usually starts within a few days and is crucial to regaining strength and range of motion in your knee.

Frequently Asked Questions

How long does the incision take to heal?

The skin usually closes within two to three weeks, and stitches or staples are removed around that time. However, the deeper tissues and bone take much longer to fully heal—typically three to six months. You will need to keep the incision clean and dry during the first few weeks and watch for signs of infection like increased redness, warmth, or drainage.

Can the surgeon see everything they need to without opening the knee all the way?

Yes. Even with a shorter incision, the surgeon can access all the damaged bone and cartilage by carefully separating the tissues around the knee. Minimally invasive techniques use specialized instruments and retractors to create a working space. The trade-off is that the surgery may take slightly longer, though the recovery is often faster.

What happens if the prosthetics don't fit right during surgery?

The surgeon tests the fit with trial pieces before cementing or press-fitting the final prosthetics. If the alignment or stability is not right, they can adjust or select a different size. In rare cases, the surgeon may need to remove and reposition a prosthetic if it is not sitting correctly, but this is uncommon because the surgeon uses guides and measurements to get it right the first time.

Is the plastic spacer between the metal parts durable?

The plastic spacer is designed to last 15 to 20 years or longer with normal use. It can wear down over time, especially if you are very active or overweight, which is why some surgeons recommend avoiding high-impact activities like running after knee replacement. If the plastic wears through, revision surgery may be needed to replace it.

Why do some surgeons use cement and others don't?

Cemented prosthetics provide when ready stability and are often preferred for older patients or those with weaker bone. Press-fit prosthetics rely on bone growing into the porous surface, which takes weeks to months but can provide a longer-lasting bond in younger, active patients. Your surgeon will recommend the best option based on your age, bone quality, and activity level.