The surgery itself lasts one to three hours, depending on whether you need one knee or both

A single knee replacement typically takes 60 to 90 minutes once you are in the operating room. If you need both knees replaced, the surgeon may do them in one session, which extends the time to two to three hours. The exact length depends on your anatomy, bone density, whether you have had previous knee surgery, and how straightforward the procedure is.

The time in the operating room is not the same as your total time at the hospital. You will spend additional time in pre-op (usually 30 to 60 minutes) where staff prepare you, place an IV, and review your medical history. After surgery, you move to recovery, where you stay for one to three hours while anesthesia wears off and nurses monitor your vital signs and pain level.

Key Takeaways

  • The actual surgical procedure takes 60 to 90 minutes for one knee, or two to three hours if both knees are done at once.
  • Plan to be at the hospital for four to six hours total, including pre-op, surgery, and recovery time.
  • You will not be able to drive or make decisions for 24 hours after anesthesia, so arrange transportation and someone to stay with you.
  • Most people go home the same day or stay overnight; your surgeon will decide based on your age, health, and pain control.

What happens before the surgeon makes the first cut

You will arrive at the hospital one to two hours before your scheduled surgery time. During pre-op, a nurse will check your blood pressure, heart rate, and oxygen level. You will change into a hospital gown, and an anesthesiologist or nurse anesthetist will place an IV line and discuss which type of anesthesia you will receive — usually general anesthesia (you are asleep) or regional anesthesia (you are awake but numb from the waist down).

The surgical team will mark the correct knee with a pen to prevent mistakes. A staff member will walk you to the operating room, where you will meet the surgeon, anesthesiologist, surgical nurses, and technicians. This pre-op phase typically takes 30 to 60 minutes and is the reason you are asked to arrive early.

The operating room timeline

Once anesthesia takes effect, the surgeon begins. The first step is removing the damaged cartilage and bone from the ends of your femur (thighbone) and tibia (shinbone). The surgeon then positions the metal implants — the femoral component on the thighbone and the tibial component on the shinbone — and cements them in place. A plastic spacer sits between the two metal parts to allow smooth movement.

The surgeon tests the knee's range of motion and alignment before closing the incision with stitches or staples. For a straightforward procedure with no complications, this entire process takes 60 to 90 minutes. If your knee has severe arthritis, previous fractures, or other damage, the surgery may take longer because the surgeon needs more time to prepare the bone surfaces.

Recovery room and discharge timing

After surgery, you move to the recovery room (also called post-anesthesia care unit, or PACU) for one to three hours. Nurses will monitor your heart rate, blood pressure, oxygen level, and pain. You will receive pain medication through your IV. Your leg will be elevated and may have ice packs to reduce swelling. Most people wake up within 15 to 30 minutes, though you may feel groggy or confused for a while longer.

Once you are alert, your pain is controlled, and you can move your leg slightly, you will be moved to a regular hospital room or discharged home. Many hospitals send patients home the same day if they meet discharge criteria: stable vital signs, controlled pain, and someone available to drive them and stay with them overnight. Some patients, particularly those over 75 or with other health conditions, stay overnight for monitoring and physical therapy.

Why the timeline varies from person to person

Your age, weight, bone quality, and overall health affect how long surgery takes. Younger patients with strong bones and no previous knee surgery often have shorter operative times. Older patients or those with osteoporosis may need extra time because the surgeon must work more carefully to position implants securely. If you have had previous knee surgery, arthroscopy, or fractures, scar tissue may slow the process.

Complications during surgery — such as bone that is more damaged than expected, difficulty positioning the implant, or bleeding — can extend the time. Your surgeon cannot predict these in advance, which is why the estimate is a range rather than an exact number.

What to expect in the hours after you leave the hospital

You will go home with pain medication, ice packs, and instructions to keep your leg elevated. You should not drive or operate machinery for at least 24 hours because anesthesia impairs judgment and reaction time, even if you feel alert. Many people experience pain, swelling, and stiffness in the first few days; this is normal and expected.

Physical therapy usually begins within one to three days after surgery. A therapist will visit your home or you will go to an outpatient clinic to learn exercises that restore your knee's range of motion and strength. The first few weeks are the most demanding; most people need pain medication and information with daily tasks like bathing and climbing stairs.

Bilateral knee replacement: doing both at once versus separate surgeries

If you need both knees replaced, your surgeon may recommend doing them in one session or scheduling them weeks or months apart. A bilateral procedure (both knees at once) takes two to three hours and means one anesthesia session, one recovery period, and one hospital stay. The advantage is that you recover from anesthesia once and begin rehabilitation on both knees simultaneously.

The disadvantage is that you will have more pain and swelling, and you will be less mobile when ready after surgery because both legs are affected. Separate surgeries mean two anesthesia sessions and two recovery periods, but you can walk and move more easily while the first knee heals. Your surgeon will recommend the approach that best fits your age, health, and ability to tolerate pain and immobility.

Frequently Asked Questions

How long will I be under anesthesia?

You will be under anesthesia for approximately 90 to 120 minutes for a single knee replacement. This includes the time it takes for anesthesia to take effect (usually 5 to 10 minutes) plus the surgical time (60 to 90 minutes). The anesthesiologist monitors you throughout and adjusts medication as needed.

Can I eat or drink before surgery?

No. You will be instructed to fast for six to eight hours before surgery — typically nothing to eat after midnight if your surgery is in the morning. This prevents food or liquid from entering your lungs during anesthesia. Your surgeon's office will give you specific fasting instructions based on your surgery time.

What if my surgery takes longer than expected?

The surgical team will contact your family in the waiting room if the procedure is taking longer than anticipated. Longer surgeries are not necessarily a sign of problems; they may straightforward mean your anatomy required more careful work. Your surgeon will explain what happened during your post-op visit.

Will I need a blood transfusion during knee replacement?

Most knee replacements do not require a transfusion. Blood loss during the procedure is usually minimal because the surgeon uses a tourniquet to limit bleeding. If your hemoglobin is low before surgery or if unexpected bleeding occurs, your surgeon may recommend a transfusion, but this is uncommon.

How soon after surgery can I walk?

You will begin walking with a walker or crutches within hours of surgery, usually while still in the recovery room or the next morning. A physical therapist will guide you through these first steps. Walking is painful but necessary to prevent blood clots and restore function. Most people walk without information within two to four weeks.