A total knee arthroplasty, commonly called a total knee replacement, is a surgical procedure that removes damaged bone and cartilage from the knee joint and replaces them with artificial components made of metal and medical-grade plastic. It is the most common joint replacement surgery performed worldwide, primarily done to relieve severe pain and restore mobility in people with advanced arthritis that hasn’t responded to other treatments.
What Gets Replaced
The knee joint is essentially a hinge where three bones meet: the femur (thighbone), the tibia (shinbone), and the patella (kneecap). In a healthy knee, smooth cartilage covers the ends of these bones and allows them to glide against each other. When that cartilage breaks down from arthritis or injury, bone grinds on bone, causing pain and stiffness.
A total knee replacement resurfaces up to three bone surfaces. The lower end of the femur is capped with a curved metal component, typically made from cobalt-chromium or titanium alloy, that mimics the bone’s natural shape. The top of the tibia receives a flat metal platform topped with a cushion of ultra-durable plastic called polyethylene, which acts as the new cartilage between the two metal surfaces. The underside of the kneecap may also be resurfaced with a dome-shaped polyethylene piece. Some newer implants use ceramics or ceramic-metal mixtures like oxidized zirconium for improved wear resistance.
Who Needs One
The primary reason people undergo this surgery is moderate-to-severe osteoarthritis that has failed all conservative treatments, including physical therapy, anti-inflammatory medications, injections, and activity modification. Surgeons evaluate the joint using weight-bearing X-rays and grade the damage on a 0-to-4 scale based on the presence of bone spurs, narrowing of the space between bones, hardening of the bone surface, and visible deformity at the bone ends. People who reach the higher end of that scale and still have significant daily pain are generally candidates.
Rheumatoid arthritis, post-traumatic arthritis from a prior injury, and certain other conditions that destroy knee cartilage can also lead to replacement. The surgery is most commonly performed on people over 60, though increasing numbers of younger patients are undergoing the procedure as implant technology improves.
What Happens During Surgery
The operation typically takes one to two hours. The surgeon makes an incision down the front of the knee and opens the joint capsule, usually through what’s called a medial parapatellar approach, which involves cutting along the inner edge of the kneecap. This provides direct access to all three bone surfaces.
Once the joint is exposed, the surgeon carefully removes the damaged cartilage and a thin layer of bone from the end of the femur, the top of the tibia, and sometimes the back of the kneecap. Precise cuts are made using alignment guides (or, increasingly, robotic systems) so the artificial components fit accurately. The new metal and plastic parts are then secured to the prepared bone surfaces. Throughout the process, the surgeon tests the knee’s range of motion and balances the surrounding soft tissues to restore normal movement patterns.
Cemented vs. Cementless Fixation
One key decision is how the implant is attached to bone. Cemented fixation uses a fast-setting bone cement to bond the metal components in place, providing immediate stability. It has been the standard approach for decades. The downside is that the cement can’t remodel the way living bone does, and repeated stress over many years can cause the cement layer to gradually fatigue and loosen.
Cementless implants have roughened or porous surfaces designed to encourage your bone to grow directly into the component, creating a biological bond. This approach preserves more bone stock and may offer better long-term durability, which makes it particularly appealing for younger, more active patients. The tradeoff is that cementless implants can cause somewhat more pain in the early weeks after surgery while the bone integrates, though this difference typically disappears within a year.
Robotic-Assisted Surgery
A growing number of surgeons now use robotic systems to assist with bone preparation and implant positioning. Robotic-assisted knee replacement doesn’t mean a robot performs the surgery. The surgeon remains in control, but uses a robotic arm guided by a 3D model of the patient’s knee to make more precise bone cuts. Studies comparing robotic-assisted to conventional manual technique show meaningful differences in accuracy: one analysis found that only 16% of robotic cases had implant positioning outside the ideal range, compared to 76% of manual cases. Robotic assistance also appears to reduce blood loss and soft tissue injury during surgery.
Risks and Complications
Total knee replacement is a safe procedure overall, with an in-hospital mortality rate of roughly 0.03%. But like any major surgery, it carries risks. The most common complication is blood clots in the deep veins of the leg, occurring in about 8 to 10% of patients, though most are caught and treated with blood thinners before they cause problems. Surgical site infection affects roughly 1 to 1.4% of patients and, when it occurs, can be serious enough to require additional surgery.
Less common complications include:
- Pulmonary embolism (a blood clot reaching the lungs): about 0.3 to 0.4%
- Pneumonia: about 0.2%
- Fracture around the implant: about 0.03%
- Stiffness or limited range of motion that may require manipulation under anesthesia
Preparing for Surgery
Preparation begins weeks or months before the actual procedure. Your surgical team will work to optimize several health factors that directly influence outcomes. If your BMI is 40 or above, most programs will ask you to lose weight before scheduling the operation. Smokers need to quit at least four weeks before surgery. People with diabetes typically need to bring their blood sugar control into a target range, and anyone taking opioid pain medication will be asked to reduce their dose by at least 50% in the month leading up to surgery.
Blood tests about four weeks before the procedure check for anemia and nutritional deficiencies that could complicate healing. At home, practical preparation matters too: setting up a bedroom on the main floor if possible, removing trip hazards, installing grab bars in the bathroom, and arranging for someone to help during the first couple of weeks.
Recovery and Rehabilitation
Most people are up and walking with assistance within 24 hours of surgery. This early movement is important because it significantly reduces the risk of blood clots and speeds the return of normal walking ability. Hospital stays have shortened considerably over the years, with many patients going home within one to two days.
Physical therapy is the backbone of recovery. In the first weeks, the focus is on regaining range of motion, reducing swelling, and building enough strength to walk safely with a walker or cane. Over the next three to six months, therapy progresses to gait training, stair climbing, and functional exercises. Most people transition from a walker to a cane within a few weeks, and many are driving again by six to eight weeks if they’ve regained enough control and are off narcotic pain medications.
How Long Implants Last
Modern knee implants are remarkably durable. Research tracking patients for at least 20 years has found survival rates between 95 and 97%, meaning only 3 to 5% of implants needed to be replaced within two decades. For most people, a knee replacement done in their 60s or 70s will last the rest of their life. Younger patients face a higher likelihood of eventually needing a revision simply because they’ll live longer and put more cumulative stress on the implant.
Satisfaction and Realistic Expectations
About 81% of patients report being satisfied or very satisfied with their knee replacement overall. Satisfaction with pain relief is high for everyday activities: 85% are happy with their ability to walk on flat ground, and 84% are satisfied with sitting and lying comfort. The numbers dip for more demanding tasks. Only 72% are satisfied with their ability to go up and down stairs, and 70% with getting in and out of a car.
These numbers reflect an important reality. A replaced knee works well for most daily activities, but it won’t feel exactly like a natural, healthy knee. High-impact activities like running and jumping are generally discouraged. Walking, cycling, swimming, golf, and light hiking are all realistic goals. The people who tend to be most satisfied are those who had realistic expectations going in: significant pain relief, better mobility for everyday life, and the ability to return to low-impact activities they enjoy.