Knee replacement surgery typically lasts between one and three hours, depending on whether you are having one knee or both replaced at the same time

The actual time the surgeon spends working on your knee — from the first incision to the last stitch — usually falls between 60 and 90 minutes for a single knee. If you are having both knees done in one session, add another 45 minutes to an hour. The total time you spend in the operating room, including setup and anesthesia, is longer: plan on two to four hours from the moment you enter until you leave for recovery.

The length varies based on your anatomy, how damaged your knee is, whether you have had previous knee surgery, and your surgeon's experience. A straightforward first replacement on a younger person with good bone quality typically takes less time than a revision surgery (replacing an implant that failed) or a replacement on someone with severe arthritis or bone loss.

Key Takeaways

  • The surgeon works on your knee for 60 to 90 minutes for one knee, or 105 to 150 minutes if replacing both knees in one surgery.
  • Your total time in the operating room, including anesthesia and setup, ranges from two to four hours.
  • Revision surgeries (replacing a failed implant) and complex cases often take longer than first-time replacements.
  • You will spend one to two hours in recovery before returning to a hospital room or going home, depending on the type of anesthesia used.

What happens during the surgery itself

The surgeon makes an incision down the front of your knee, usually four to six inches long. They then remove the damaged cartilage and bone from the end of your thighbone and the top of your shinbone, and cement or screw the metal implant pieces into place. They test the knee's movement and alignment before closing the incision with stitches or staples.

Most of this time is spent preparing the bone surfaces and positioning the implant correctly. Rushing this step increases the risk of misalignment, which can cause pain and early wear on the implant. Surgeons who take slightly longer at this stage often report better long-term outcomes.

Time in the operating room versus time on the table

When your surgeon says the surgery took 90 minutes, they usually mean the time from incision to closure. But you will be in the operating room for longer. Before the surgeon begins, the anesthesiologist places your IV, monitors, and spinal or general anesthesia (usually 15 to 20 minutes). The surgical team then positions you, cleans your leg with antiseptic, and drapes the area (another 10 to 15 minutes).

After the surgeon finishes, you are moved to the recovery room while still under anesthesia. You wake up gradually over the next 30 to 60 minutes as the anesthesia wears off. Nurses monitor your blood pressure, heart rate, oxygen level, and pain. This is when you receive pain medication if needed. Total time from entering the operating room to leaving recovery is typically two to four hours.

Why some surgeries take longer than others

A revision surgery — replacing an implant that has loosened, worn out, or become infected — takes longer because the surgeon must remove the old implant and cement, then prepare the bone for a new one. This can add 30 to 60 minutes to the procedure. Bone loss from the failed implant may require bone grafting, which adds more time.

Severe arthritis with bone-on-bone damage, obesity, previous knee surgery, or poor bone quality can also extend the time. Younger patients with good bone density and no previous surgery usually have shorter, more straightforward procedures. Your surgeon can give you a better estimate once they review your X-rays and medical history.

What to expect in recovery after surgery

You will wake up in the recovery room with your knee wrapped in a compression bandage and possibly in a cooling device to reduce swelling. A catheter may be in place to drain fluid from the surgical site. You will not be able to walk or bear weight on the leg when ready — this takes days to weeks of physical therapy.

Most people go home the same day or stay one night in the hospital. Before discharge, you will receive crutches or a walker, pain medication, and instructions for wound care and physical therapy. The first few weeks at home focus on reducing swelling, regaining motion, and gradually putting weight on the leg. Full recovery — returning to normal activities without pain — typically takes three to six months.

Anesthesia type and how it affects your time in surgery

Most knee replacements use either spinal anesthesia (numbing from the waist down while you sleep lightly) or general anesthesia (you are fully asleep). Spinal anesthesia takes slightly less time to administer and wears off faster, so you may wake up sooner. General anesthesia takes a few minutes longer to set up but allows the surgeon to position your leg however they need without you moving.

The choice between the two does not significantly change how long the surgery itself takes, but it does affect how long you spend in recovery. Patients under spinal anesthesia often wake up alert within 30 to 45 minutes, while general anesthesia patients may take 45 to 60 minutes to fully wake. Your anesthesiologist will discuss which option is safer for you based on your age, weight, and medical history.

Single knee versus both knees at once

If you need both knees replaced, your surgeon may recommend doing them in one session or scheduling them weeks or months apart. A bilateral replacement (both at once) takes longer — typically two and a half to three and a half hours total — but you have one recovery period instead of two. You will spend more time in the operating room and recovery room, but you avoid a second surgery and a second round of anesthesia.

The downside is that you cannot put weight on either leg when ready, so you will need more help at home during the first weeks. Many surgeons prefer to do one knee first, let you recover and regain strength, then do the other. This approach takes longer overall but is often easier to manage at home. Your surgeon will recommend the approach that makes the most sense for your situation.

Frequently Asked Questions

How long will I be asleep during knee replacement surgery?

You will be under anesthesia for the entire procedure, which is typically two to four hours from the moment you enter the operating room. The actual surgery — from incision to closure — takes 60 to 90 minutes. You will not be aware of any of this time. You wake up gradually in the recovery room as the anesthesia wears off.

Can the surgeon tell me exactly how long my surgery will take?

Your surgeon can give you an estimate based on your X-rays, age, and medical history, but the exact time will not be known until they begin. If your bone is softer than expected or the implant needs adjustment, the surgery may take longer. Your surgeon will update your family in the waiting room if the procedure takes significantly more time than expected.

What if my surgery takes longer than three hours?

Longer surgeries are not necessarily a sign of problems — they may mean your surgeon is taking extra time to may support perfect alignment or dealing with unexpected bone loss. Revision surgeries and complex cases routinely take three to four hours. Your surgeon will explain what took longer when you see them after recovery.

Do I need to fast before surgery, and how long does that take?

Yes, you will be asked to stop eating at midnight the night before surgery and stop drinking clear liquids two hours before arrival. This prevents nausea and vomiting during anesthesia. The fasting itself takes no time — it is just a waiting period. You will eat again a few hours after surgery once you are alert and your stomach is settled.

How long until I can walk after knee replacement?

You will begin walking with a walker or crutches within hours of surgery, usually the same day. At first you will only take a few steps with help from a physical therapist. Over the next two to four weeks, you will gradually put more weight on the leg and transition from crutches to a cane. Most people walk without information by six to eight weeks, though full strength and normal gait take longer.