The basic sequence: what happens during knee replacement surgery

A knee replacement takes about one to three hours. The surgeon removes the damaged cartilage and bone from the end of your thighbone, shinbone, and kneecap, then attaches metal and plastic implants to replace those surfaces. The surgery happens under general anesthesia (you are asleep) or regional anesthesia (your leg is numb but you are awake). A tourniquet—a tight band around your upper thigh—stops blood flow to the leg so the surgeon can see clearly.

The surgeon makes an incision down the front of your knee, usually 8 to 10 inches long, though some surgeons use smaller incisions. They move the kneecap to the side to reach the joint underneath. Once the damaged bone and cartilage are removed, the surgeon shapes the remaining bone to fit the implant components precisely. Metal parts are either cemented to the bone or press-fit (held in place by friction and bone growth). A plastic spacer goes between the metal parts to create a smooth gliding surface.

Key Takeaways

  • The surgeon removes damaged bone and cartilage from your thighbone, shinbone, and kneecap, then attaches metal and plastic implants to replace those surfaces.
  • The incision is typically 8 to 10 inches long on the front of the knee, though some surgeons use smaller approaches.
  • A tourniquet stops blood flow during surgery so the surgeon can see the joint clearly without excessive bleeding.
  • Metal parts are either cemented to the bone or press-fit, depending on your age, bone quality, and the surgeon's preference.
  • The surgery usually takes one to three hours, and you go home the same day or stay overnight depending on your health and recovery plan.

Preparing the bone surfaces for the implant

Once the surgeon has access to the joint, they use specialized cutting guides and saws to remove the damaged surfaces in a precise pattern. The thighbone (femur) is cut at a specific angle so the implant will sit correctly. The shinbone (tibia) is also cut flat. The kneecap (patella) is cut on its back surface. These cuts are made to exact measurements—often using computer-assisted navigation or robotic guidance—so the implant components align properly.

The surgeon then tests the fit by inserting trial (temporary) implant pieces. This trial fit lets them check that your knee bends and straightens smoothly, that the alignment is correct, and that the ligaments around the knee are balanced. If adjustments are needed, the surgeon makes them now. Once the fit is confirmed, the trial pieces come out and the real implants go in.

Attaching the metal and plastic components

The femoral component (the part that replaces the end of your thighbone) is usually made of cobalt-chromium or titanium alloy. The tibial component (for your shinbone) is also metal, with a plastic spacer attached or inserted on top. The patellar component (for your kneecap) is smaller and made of plastic or metal-backed plastic.

These components are fixed to your bone in one of two ways. Cemented fixation uses a special bone cement (polymethylmethacrylate) that hardens and bonds the implant to the bone—this is the most common method and works well for older patients or those with weaker bone. Press-fit or cementless fixation relies on the implant's textured surface to grip the bone directly; bone grows into the implant over time. Surgeons choose based on your age, bone quality, and activity level. Some implants use a hybrid approach: cement on one part, press-fit on another.

Closing the incision and managing bleeding

After the implants are in place, the surgeon removes the tourniquet so blood flow returns to your leg. They check for any bleeding and control it with cautery (heat) or sutures. The joint capsule and soft tissues are closed with stitches or sutures. The skin is closed with stitches, staples, or skin adhesive, depending on the surgeon's preference.

A drain may be left in place for 24 to 48 hours to prevent fluid buildup in the knee. Your leg is wrapped in a compression bandage to reduce swelling. You wake up in the recovery room, and nurses monitor your vital signs and pain level. Most people go home the same day or stay one night in the hospital.

Variations in surgical approach

Traditional knee replacement uses a single long incision down the front of the knee. Minimally invasive surgery uses one or two smaller incisions (4 to 6 inches) and specialized instruments to reach the joint. Smaller incisions may mean less muscle damage, less pain, and faster early recovery—though the long-term outcome is similar to traditional surgery.

Robotic-assisted surgery uses a robotic arm guided by the surgeon to make precise bone cuts and position implants. The surgeon controls the robot and makes all decisions; the robot does not operate independently. Studies show robotic guidance can improve alignment accuracy, though whether this translates to better long-term results is still being studied. Robotic surgery typically costs more and takes slightly longer.

Outpatient knee replacement is becoming more common at specialized surgical centers. You have surgery in the morning and go home the same day with a detailed home care plan. This requires good home support, reliable transportation, and a surgeon experienced in rapid discharge protocols.

What happens to your old knee joint

The bone and cartilage removed during surgery cannot be reused or transplanted. They are disposed of as medical waste. The implants are designed to last 15 to 20 years on average, though some last longer and some wear out sooner depending on your activity level, weight, and how well you follow post-surgery care.

If an implant fails or wears out, a second surgery called revision knee replacement can be performed. Revision surgery is more complex than the first replacement because the surgeon must remove the old implant, clean up the bone, and attach a new one. The bone may have thinned or weakened, requiring bone grafts or special implant designs. Recovery from revision surgery is typically longer than from the first replacement.

Pain management and anesthesia during surgery

You receive anesthesia before the incision is made, so you feel no pain during the procedure. General anesthesia puts you to sleep; regional anesthesia (spinal or epidural) numbs your leg while you remain awake or lightly sedated. Your anesthesiologist monitors your heart rate, blood pressure, oxygen level, and breathing throughout surgery.

After surgery, you manage pain with medications prescribed by your surgeon—usually a combination of oral pain relievers, anti-inflammatory drugs, and sometimes opioids for the first few days. Ice, elevation, and compression also reduce pain and swelling. Physical therapy begins within hours or days, and movement itself helps control pain by preventing stiffness.

Frequently Asked Questions

How long does the actual surgery take?

Most knee replacements take one to three hours from the time you enter the operating room until the incision is closed. Minimally invasive surgery may take slightly longer because the smaller incisions require more careful maneuvering. Revision surgery (replacing an old implant) usually takes longer than a first replacement.

Will I be awake during knee replacement surgery?

You can choose general anesthesia (asleep) or regional anesthesia (awake but numb). Most people choose general anesthesia because they prefer not to be aware during surgery. Regional anesthesia is safe and some patients prefer it, but your anesthesiologist will discuss which option is best for your health and preferences.

What is the tourniquet and why is it used?

A tourniquet is a tight band placed around your upper thigh before surgery. It stops blood flow to your lower leg so the surgeon can see the joint clearly without blood obscuring the view. The tourniquet is removed after the implants are in place and the incision is being closed. Tourniquet time is usually 60 to 90 minutes.

Can the surgeon use a smaller incision to reduce scarring?

Minimally invasive techniques use smaller incisions (4 to 6 inches instead of 8 to 10 inches), which may result in less visible scarring and less muscle damage. However, not all surgeons offer this approach, and it requires specialized training and equipment. Ask your surgeon whether they perform minimally invasive knee replacement and whether you are a good candidate.

What happens if the implant is cemented versus press-fit?

Cemented implants are bonded to bone with special cement and are stable when ready; they work well for older patients and those with weaker bone. Press-fit implants rely on bone growth to find them over time and may be preferred for younger, more active patients. Both methods have good long-term success rates. Your surgeon will recommend based on your age and bone quality.