What happens during knee replacement surgery
A knee replacement removes the damaged surfaces of your thighbone, shinbone, and kneecap, then covers them with metal and plastic parts shaped like a normal knee joint. The surgeon makes an incision down the front of your knee, usually 8 to 10 inches long, and carefully removes the worn cartilage and bone. Metal implants are then attached to the ends of your thighbone and shinbone using either cement or a press-fit method that lets bone grow into the implant. A plastic spacer sits between the metal parts to act like your natural cartilage. The kneecap is resurfaced with a plastic button. The whole procedure takes about one to two hours.
Most knee replacements are performed under general anesthesia, meaning you are asleep during the operation. Some surgeons use regional anesthesia instead, which numbs everything below your waist while you remain conscious. Your surgical team monitors your heart rate, blood pressure, and oxygen levels throughout. Once the implants are in place and the surgeon confirms proper alignment and movement, the incision is closed with stitches or staples.
Key Takeaways
- The surgeon removes damaged bone and cartilage from your thighbone, shinbone, and kneecap, then attaches metal and plastic implants to create a new joint surface.
- The procedure takes one to two hours and uses either general anesthesia (you sleep) or regional anesthesia (lower body numb).
- Most people stay in the hospital for one to three days, though some go home the same day depending on their health and the surgeon's preference.
- Physical therapy begins within days of surgery and continues for several weeks to restore strength, flexibility, and walking ability.
- Full recovery typically takes three to six months, though improvement continues for up to a year as swelling decreases and muscles strengthen.
Why surgeons recommend knee replacement
Knee replacement is usually recommended when arthritis or injury has worn away the cartilage that cushions your knee joint, causing pain that limits daily activities and does not improve with medication, injections, or physical therapy. Osteoarthritis is the most common reason — it develops over years as the protective cartilage gradually breaks down. Rheumatoid arthritis, post-traumatic arthritis from an old injury, or avascular necrosis (when bone dies from lack of blood supply) can also damage the knee enough to warrant replacement.
Your surgeon will typically recommend replacement when you have chronic pain that interferes with walking, climbing stairs, or getting in and out of chairs, and when X-rays show significant cartilage loss. Age alone is not a barrier — people in their 50s, 60s, 70s, and beyond have successful replacements. The decision balances how much your knee limits you against the risks and recovery demands of surgery.
Hospital stay and when ready recovery
Most patients stay in the hospital for one to three days after knee replacement. On the day of surgery, you wake in the recovery room with your knee wrapped in compression bandages and possibly in a cooling device to reduce swelling. Pain medication is given regularly, and you may receive antibiotics to prevent infection. A catheter may be placed to drain fluid from the surgical site for the first day or two.
Physical therapists visit you on the day of surgery or the next morning to begin gentle movement. You will be asked to bend and straighten your knee, even though it is uncomfortable, because movement prevents stiffness and blood clots. A nurse or therapist helps you stand and walk short distances using a walker or crutches. Most people can put some weight on the leg within hours of surgery, though how much depends on your surgeon's instructions and your comfort level.
Before you leave the hospital, you receive instructions on wound care, pain management, activity limits, and when to call your surgeon. You will need someone to drive you home and help you for at least the first week. Your surgeon schedules a follow-up visit within two weeks to check the incision and remove stitches or staples.
Physical therapy and regaining movement
Physical therapy is the most important part of recovery and begins before you leave the hospital. A therapist works with you to gradually increase how far you can bend your knee and how much weight you can put on it. Early exercises are straightforward — straightening your leg, tightening your thigh muscle, or sliding your heel toward your buttock — but they prevent your knee from stiffening and help your muscles support the new joint.
Most people do physical therapy two to three times per week for four to six weeks after surgery, then continue exercises at home. Your therapist teaches you movements to do daily, usually taking 20 to 30 minutes. Progress is measured by how far you can bend your knee (called flexion) and how straight you can make it (called extension). Most people reach 90 to 110 degrees of bending by six weeks, though full bending may take several months.
Pain and swelling during therapy are normal and do not mean something is wrong. Ice, elevation, and compression help manage both. Your surgeon may recommend over-the-counter pain relievers or prescribe stronger medication for the first few weeks. Returning to activities too quickly can cause setbacks, so your therapist guides what is safe at each stage.
Timeline for returning to normal activities
Most people can walk without a walker or crutches within two to four weeks, though walking distance and speed improve gradually. Driving is usually possible four to six weeks after surgery once you can bend your knee enough to sit comfortably in a car and have stopped taking strong pain medication. Returning to work depends on your job — desk work may be possible within four to six weeks, while jobs requiring standing or walking take longer.
Light activities like swimming or stationary cycling can often resume around six to eight weeks. High-impact activities like running, jumping, or contact sports are generally not recommended, though many people walk, hike, golf, and do other low-impact activities without limitation. Your surgeon will give you specific guidance based on your implant type and your individual recovery.
Full recovery typically takes three to six months, though some people continue improving for up to a year as swelling decreases and muscles strengthen. Most people report significant pain relief and improved function within three months. Fatigue is common in the first few weeks and gradually improves as your body heals.
Risks and complications to know about
Serious complications are uncommon but possible. Infection occurs in fewer than 2 percent of cases and is treated with antibiotics or, rarely, additional surgery. Blood clots can form in your leg after surgery — your surgeon may recommend blood thinners or compression stockings to reduce this risk. Stiffness happens when scar tissue limits knee bending, though aggressive physical therapy usually prevents it. Implant loosening or wear can occur over many years, potentially requiring revision surgery.
Less serious but more common issues include swelling that lasts weeks or months, bruising, temporary numbness around the incision, and difficulty sleeping due to pain or discomfort. Most of these resolve with time and do not affect the long-term success of your replacement. Your surgeon will discuss your individual risk factors during your pre-surgery consultation.
How long knee replacements last
Most modern knee implants last 15 to 20 years or longer. Studies show that 85 to 90 percent of knee replacements are still functioning well after 20 years. Implant life depends on the materials used, how well your body accepts the implant, your activity level, and your body weight. Heavier stress on the joint from high-impact activities or excess weight can shorten implant life, while low-impact activities and maintaining a healthy weight support longevity.
If your implant does wear out or loosen, revision surgery can replace it, though revision surgery is more complex and recovery is longer than the first replacement. Many people never need revision surgery. Your surgeon will monitor your implant during regular check-ups and can detect problems before they cause symptoms.
Frequently Asked Questions
Will I set off metal detectors after knee replacement?
Yes, most knee implants contain metal and will trigger metal detectors at airports and security checkpoints. Your surgeon provides a card stating you have a metal implant, which you can show to security. You can still fly and travel — just inform security in advance and be prepared for additional screening.
Can I kneel or sit cross-legged after knee replacement?
Many people can kneel and sit cross-legged after full recovery, though it may feel uncomfortable at first. Your physical therapist can work with you on these movements if they matter for your daily life or hobbies. Some people choose not to kneel regularly to reduce stress on the implant, but occasional kneeling is generally safe.
What happens if I gain weight after my knee replacement?
Extra weight increases stress on your implant and can accelerate wear, potentially shortening how long it lasts. Maintaining a stable weight supports your implant's longevity and reduces pain and swelling. If you gain weight after surgery, your surgeon can discuss whether weight management would help your long-term outcome.
Do I need antibiotics before dental work after knee replacement?
Most surgeons no longer recommend antibiotics before routine dental work for people with knee implants. However, if you have a dental procedure involving significant bleeding or infection risk, discuss it with your surgeon beforehand. They will advise based on your individual situation and implant type.
Can I have an MRI after knee replacement?
Most modern knee implants are MRI-safe, though some older implants are not. Your surgeon will tell you whether your specific implant can be scanned. If you need an MRI, inform the imaging center that you have a knee implant so they can verify safety and adjust settings if needed.