What happens during a knee replacement
A knee replacement removes the damaged parts of your knee joint and replaces them with artificial components made of metal and plastic. The surgeon makes an incision down the front of your knee, usually 8 to 10 inches long, to access the joint. 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 artificial parts into place. The surgery typically takes 1 to 2 hours, though the entire time you spend in the operating room—including preparation and recovery from anesthesia—is usually 2 to 3 hours.
You will be asleep under general anesthesia during the procedure, so you won't feel pain or remember the surgery. A regional anesthetic (numbing the leg without putting you fully asleep) is sometimes used instead, depending on your health and your surgeon's preference. Either way, you won't be conscious during the operation.
Key Takeaways
- The surgeon removes damaged bone and cartilage from your thighbone and shinbone, then attaches artificial metal and plastic components using cement or screws.
- The incision is typically made down the front of the knee and is 8 to 10 inches long; the entire procedure takes 1 to 2 hours of actual surgery time.
- You will be under anesthesia and asleep during the operation, with a catheter placed to drain urine since you cannot use the bathroom while unconscious.
- Most people stay in the hospital for 1 to 3 days after surgery, though some go home the same day depending on their health and home support.
- Physical therapy begins within 24 hours and continues for several weeks to restore movement and strength in your new knee.
The surgical approach and incision
Your surgeon will position you on your back on the operating table. They clean the skin around your knee with an antiseptic solution and drape the area with sterile sheets, leaving only the knee exposed. The incision is made vertically down the front of the knee, usually starting just above the kneecap and extending a few inches below it. This approach gives the surgeon direct access to the joint without cutting through major muscles.
Once the skin is open, the surgeon moves aside the tissues and muscle to reach the joint capsule—the membrane that surrounds your knee. They then open the capsule to see the damaged bone and cartilage inside. The exact size and placement of the incision can vary slightly depending on your anatomy and the surgeon's technique, but the front-of-knee approach is standard for most total knee replacements.
Removing damaged bone and cartilage
The surgeon uses specialized cutting guides and saws to remove the damaged surfaces from the end of your thighbone (femur) and the top of your shinbone (tibia). These cuts are made at precise angles to match the shape of the artificial components. The amount of bone removed is usually quite small—often just a few millimeters—because the goal is to preserve as much healthy bone as possible.
The surgeon also removes any remaining cartilage and bone spurs from the joint surfaces. If your kneecap (patella) is also damaged, the surgeon may resurface it by removing the damaged cartilage and cementing a plastic button onto the back of the kneecap. Not all knee replacements include a patellar component; your surgeon will decide based on the condition of your kneecap and your specific situation.
Placing the artificial components
Once the bone surfaces are prepared, the surgeon positions the artificial components to check the fit and alignment. The femoral component (the part that replaces the end of your thighbone) is typically made of cobalt-chromium metal. The tibial component (which sits on top of your shinbone) has a metal base with a plastic spacer on top. Some surgeons use cement to bond these parts to your bone; others use a press-fit technique where the components are designed to grip the bone directly, allowing bone to grow into them over time.
If cement is used, the surgeon cleans the bone surfaces and applies a special bone cement, then presses the components into place and holds them steady while the cement hardens—a process that takes a few minutes. The surgeon checks the alignment and stability of the components before moving forward. Any excess cement is removed before it fully hardens.
Closing the incision and recovery in the operating room
Once the artificial components are find, the surgeon closes the joint capsule with stitches and then closes the layers of tissue and muscle. The skin is closed with stitches, staples, or surgical glue, depending on your surgeon's preference. A sterile bandage is applied over the incision, and your leg may be wrapped with an elastic bandage to help control swelling.
Before you leave the operating room, the surgical team will place a catheter (a thin tube) in your bladder to drain urine, since you won't be able to use the bathroom while you're still under anesthesia and heavily medicated. This catheter is usually removed within 24 hours once you're alert and able to get out of bed. You'll also receive pain medication and possibly antibiotics through an IV line that stays in place for the first day or two.
Hospital stay and when ready aftercare
Most people stay in the hospital for 1 to 3 days after knee replacement surgery. Some hospitals and surgical centers now offer same-day discharge for patients who have good home support and meet certain health criteria, but this is less common. During your hospital stay, nurses will monitor your vital signs, manage your pain, and watch for any signs of infection or blood clots.
Physical therapy typically begins within 24 hours of surgery, even while you're still in the hospital. A physical therapist will help you move your new knee gently, teach you how to use crutches or a walker, and show you exercises to prevent stiffness. You'll also learn how to care for your incision and recognize warning signs like increased redness, warmth, or drainage that might indicate infection.
What happens to the removed bone and cartilage
The bone and cartilage removed during surgery are treated as medical waste and are not returned to you. They cannot be reused or transplanted. This is why knee replacement is considered a permanent change—once the damaged surfaces are removed and replaced with artificial components, your knee joint is fundamentally different from before.
Some patients ask whether their removed tissue can be preserved or used later. In the case of knee replacement, this is not medically useful or necessary. The artificial components are designed to last many years and function independently of your original bone and cartilage.
Frequently Asked Questions
How long does the actual surgery take?
The actual surgical time is usually 1 to 2 hours. However, you'll be in the operating room for 2 to 3 hours total because of time spent preparing you, positioning you, and allowing you to wake up from anesthesia. Your surgeon can give you a more specific estimate based on your individual situation.
Will I feel pain during the surgery?
No. You will be asleep under general anesthesia or numbed with regional anesthesia, so you won't feel pain or be aware of what's happening. You may feel some pressure or hear sounds, but you won't experience pain during the procedure.
Can a knee replacement be done without cutting through muscle?
Most knee replacements use the standard front-of-knee approach, which does move muscle aside but doesn't cut through it. Some surgeons use a minimally invasive technique with a smaller incision, though this is not appropriate for all patients. Ask your surgeon which approach they recommend for your specific knee.
What if the surgeon finds more damage than expected during surgery?
If your surgeon discovers additional damage—such as severe damage to the kneecap or ligaments—they may need to adjust their plan during the surgery. This might mean a longer incision, additional components, or a different type of replacement. Your surgeon will discuss any major changes with you when you wake up.
How soon after surgery can I put weight on my new knee?
Most people can begin putting weight on their new knee within 24 hours, often with crutches or a walker for support. Your physical therapist will guide you on how much weight to put on it and when you can progress to walking without aids. Full weight-bearing is usually possible within a few weeks, though recovery continues for several months.