TKR surgery, or total knee replacement, is an operation that removes damaged cartilage and bone from your knee joint and replaces them with metal and plastic components that mimic the knee’s natural movement. It is one of the most commonly performed orthopedic surgeries, with nearly 90% of patients reporting satisfaction one year after the procedure. Most people who get a TKR have severe osteoarthritis, though rheumatoid arthritis and serious knee injuries can also lead to it.
Why People Get a Knee Replacement
The knee joint is covered in smooth cartilage that lets the bones glide against each other. When that cartilage wears away, bone grinds on bone, causing pain, swelling, and stiffness that can make walking, climbing stairs, or even sitting down difficult. Total knee replacement was originally considered a last resort for people with advanced joint destruction, severe pain, and major limitations in mobility. Today, surgeons operate on a wider range of patients, including those with moderately narrowed joint space, people under 55, and those whose arthritis affects only one section of the knee.
That said, surgery isn’t appropriate for everyone with knee pain. People who report only mild discomfort and minimal limitations in daily activities may not benefit. If imaging shows little or no narrowing of the joint space, the gains from surgery are uncertain. The strongest candidates are those whose pain and loss of function are significant enough that nonsurgical treatments like physical therapy, injections, and anti-inflammatory medications have stopped providing adequate relief.
What Happens During the Surgery
The operation typically takes one to two hours. After anesthesia (usually spinal or general), the surgeon makes an incision over the front of the knee and opens the joint capsule. The kneecap is moved to the side, and the knee is bent to expose the damaged surfaces.
The surgeon begins by reshaping the end of the thighbone (femur). A guide rod is inserted into the bone’s central canal to ensure cuts are made at the correct angle, usually around 5 to 7 degrees off vertical to match your leg’s natural alignment. Roughly 9 to 10 millimeters of bone is removed from the bottom of the femur. Several additional cuts shape the bone to fit the contours of the metal implant precisely.
Next, the top of the shinbone (tibia) is cut flat using a guide aligned perpendicular to the bone’s long axis. After each cut, the surgeon checks the gaps created when the knee is fully straight and fully bent, adjusting as needed so the joint will be balanced and stable through its full range of motion. Retractors protect the ligaments on either side of the knee throughout the process. In some cases, the undersurface of the kneecap is also resurfaced with a plastic button.
What the Implant Is Made Of
A knee replacement has three main parts. The femoral component, which caps the end of the thighbone, is typically made from a cobalt-chromium alloy, chosen for its strength and smooth surface. The tibial component, a flat tray that sits on top of the shinbone, is often made from a titanium alloy. Between these two metal pieces sits a plastic spacer made from ultra-high-molecular-weight polyethylene, a dense polymer that acts as the new cartilage, allowing the joint to glide with minimal friction. If the kneecap is resurfaced, that button is also polyethylene.
These materials are designed to withstand decades of use. Data from national joint registries covering hundreds of thousands of patients show that 93% of total knee replacements are still functioning at 15 years, 90% at 20 years, and over 82% at 25 years.
Robotic-Assisted vs. Manual Technique
Traditional knee replacement relies on handheld cutting guides and the surgeon’s experience to position the implant. Robotic-assisted surgery adds a layer of technology: a CT scan taken before the operation creates a 3D model of your knee, and during surgery a robotic arm helps the surgeon make bone cuts within a predefined boundary, reducing the chance of removing too much or too little bone.
Early comparisons suggest measurable differences in recovery. In one study, patients who had robotic-assisted surgery stayed in the hospital an average of 1.18 days compared to 1.73 days for manual surgery. They also needed about 27% less opioid pain medication in the hospital and required fewer physical therapy visits afterward (11 versus 13). Thirty-day readmission rates trended lower with the robotic approach (0.7% vs. 4.3%), though that difference didn’t quite reach statistical significance. By the one-year mark, functional outcomes between the two groups tend to converge. Robotic-assisted surgery is becoming more widely available, but both approaches produce reliable long-term results.
Recovery Timeline
Most people can put weight on the new knee the same day as surgery, using a walker or crutches for support. Hospital stays have shortened dramatically. In 2012, only 0.4% of knee replacements were done on an outpatient (same-day) basis. By 2020, that figure had risen to 14.1%. Many patients who aren’t candidates for same-day discharge go home after one or two nights.
The first two weeks focus on controlling swelling, regaining the ability to straighten your knee fully, and building enough strength to move safely around your home. By about six weeks, most people can resume everyday activities like light housework, short drives, and desk work. Full recovery, meaning the point where the knee feels natural and you’ve regained your strength and flexibility, generally takes about a year.
Physical Therapy After Surgery
Rehabilitation is the single biggest factor in how well your new knee performs. The primary goals are restoring range of motion and rebuilding quadriceps strength, since the muscles on the front of the thigh weaken significantly after surgery.
Therapy usually starts within hours of the operation, beginning with simple bed exercises: rolling to either side, scooting, and moving from lying flat to sitting up. Within the first day or two, you’ll practice standing from a seated position and taking your first steps. During the hospital stay, sessions may happen twice a day.
After discharge, most rehab programs involve two to three sessions per week for the first six weeks, then tapering to once or twice a week for several more weeks. Early sessions focus on achieving full passive and active range of motion, meaning both how far the therapist can move your knee and how far you can move it yourself. As you progress, exercises expand to include stationary cycling, outdoor walking, targeted muscle strengthening (especially the inner quadriceps), balance training, and stretching. A home exercise program runs alongside your formal sessions, and consistency with those daily exercises matters as much as the clinic visits.
Risks and Complications
Knee replacement is considered safe, but like any major surgery it carries risks. The two most closely monitored complications are blood clots and infection.
Without preventive treatment, deep vein thrombosis (a blood clot in the leg) occurs in 40 to 88% of knee replacement patients. That’s why blood-thinning medication and compression devices are standard after surgery. With these precautions, the risk drops substantially. A clot that travels to the lungs (pulmonary embolism) causes symptoms in 0.5 to 3% of cases.
Infection of the joint is less common but serious. When it occurs in the weeks after surgery, it typically requires additional procedures and extended antibiotics. Stiffness is another potential issue. Some patients develop excess scar tissue that limits knee bending, occasionally requiring a procedure under anesthesia to break up the adhesions. Implant loosening, nerve or blood vessel injury, and persistent pain are rarer but possible. Overall, the complication rate is low enough that nearly 90% of patients in modern studies report being satisfied with the outcome at one year, with significant improvements in pain scores, physical function, and mental well-being compared to their preoperative state.