A total knee replacement removes the damaged surfaces of your knee joint and caps them with metal and plastic components that recreate the joint’s natural movement. The surgery typically takes 60 to 90 minutes, involves precise bone cuts guided by alignment jigs or robotic tools, and most patients go home within three days. Here’s what happens before, during, and after the procedure.
What Happens Before Surgery
Preparation starts weeks before your surgery date. Your surgical team will review imaging of your knee, usually X-rays, to plan the exact angles of the bone cuts and choose the right implant size. You’ll need medical clearance, which may involve blood work and a review of any existing health conditions. If you need dental work, get it done at least six weeks beforehand. Bacteria from dental procedures can enter the bloodstream and settle around a new joint, so your surgery will actually be delayed if you have active dental problems at the time.
You’ll be told which medications to stop taking in advance, particularly blood thinners. Many surgeons also recommend “prehab,” a set of strengthening exercises you start before the operation. Building up the muscles around your knee ahead of time makes a measurable difference in how quickly you recover afterward.
Anesthesia Options
You won’t necessarily be put fully under for a knee replacement. The two main options are general anesthesia (fully asleep) and spinal anesthesia (numb from the waist down while you remain conscious or lightly sedated). General anesthesia has historically been the more common choice in the U.S., but spinal anesthesia is gaining ground because it tends to produce better outcomes. A large study of over 14,000 patients found that those who received spinal anesthesia had lower rates of wound infection, needed fewer blood transfusions, and had shorter surgeries and hospital stays compared to general anesthesia. Patients who received spinal anesthesia also had significantly lower 30-day mortality rates: 0.10% versus 0.18% for general anesthesia.
On top of whichever primary method is used, most surgeons add a nerve block to control pain after surgery. The two most common are a femoral nerve block and an adductor canal block. The femoral nerve block is highly effective, reducing pain and opioid use for the first 72 hours, but it also temporarily weakens the quadriceps muscle, which can increase fall risk. The adductor canal block targets sensory nerves only, leaving your muscle strength largely intact. Your anesthesiologist will recommend the best combination based on your health.
The Surgical Steps
Once anesthesia takes effect, the surgeon makes an incision down the front of the knee, typically 8 to 10 inches long. The most common approach goes through the inner edge of the quadriceps tendon and along the kneecap. The kneecap is flipped to the side, and the knee is bent to expose the joint surfaces.
Bone Preparation
The surgeon removes the damaged cartilage and a thin layer of bone from three surfaces: the bottom of the thighbone (femur), the top of the shinbone (tibia), and sometimes the underside of the kneecap. These cuts need to be extraordinarily precise because even a degree or two of misalignment changes how the new joint tracks and wears over time.
For the thighbone, a guide rod is inserted into the bone’s inner canal, and an alignment jig is attached to set the cutting angle, typically 5 to 7 degrees off vertical to match your leg’s natural alignment. Most surgeons remove about 9 to 10 millimeters of bone from the end of the femur. For the shinbone, a separate guide ensures the cut is perpendicular to the bone’s long axis. The surgeon references landmarks on the shin and ankle to set the rotation correctly.
After these two major cuts, the surgeon checks the “extension gap,” the space between the cut bones when your leg is straight. A spacer block is inserted and an alignment rod is used to confirm everything is balanced side to side. Then the “flexion gap” is checked with the knee bent, ensuring the joint will be stable through its full range of motion. Only after both gaps are confirmed does the surgeon make the remaining shaping cuts: anterior, posterior, and chamfer cuts on the thighbone that create a precise profile for the implant to sit on.
Implant Placement
The knee replacement has three main parts. The femoral component is a smooth, curved metal cap (usually cobalt-chromium alloy or a newer ceramic-metal hybrid called oxidized zirconium) that fits over the reshaped end of the thighbone. The tibial component is a flat metal tray that sits on top of the cut shinbone, with a smooth plastic insert snapped onto it. This plastic spacer, made from ultra-high-molecular-weight polyethylene, acts as the new cartilage, providing a low-friction surface for the metal cap to glide on. If the underside of the kneecap is also resurfaced, a small plastic button is cemented there.
Most implants are fixed to the bone with bone cement, which hardens in minutes and creates an immediate bond. Some designs use a porous metal surface that allows bone to grow into the implant over time, but cemented fixation remains the standard for total knee replacements.
Once the components are in place, the surgeon tests the knee through its full range of motion, checking that it bends and straightens smoothly, that the kneecap tracks properly, and that the ligaments on either side hold the joint stable. The incision is then closed in layers.
Robotic-Assisted Surgery
Some surgeons use robotic systems to guide the bone cuts. The robot doesn’t perform the surgery on its own. Instead, it uses preoperative imaging to create a 3D model of your knee, then provides real-time feedback as the surgeon cuts, helping stay within the planned angles. The idea is greater precision in implant alignment and soft tissue balance.
Results are mixed depending on the system. A meta-analysis of randomized trials found that robotic-assisted surgery offered advantages in implant alignment and reduced postoperative pain with certain systems (NAVIO and YUANHUA), while the widely used MAKO system showed less favorable alignment outcomes. Robotic cases also had a higher rate of conversion to traditional open surgery, 10% versus 2%. The technology is evolving, and whether it translates to better long-term outcomes for most patients remains an open question.
Hospital Stay and Early Recovery
Hospital stays have dropped significantly. In 2010, the median stay for a total knee replacement was about 4.4 days. By 2022, that had fallen to just under 3 days, based on data from nearly 1.5 million procedures in England. Some centers are now performing knee replacements as same-day outpatient procedures for selected patients, sending them home within hours.
You’ll start physical therapy the day of surgery or the morning after. The initial focus is on bending the knee and getting you walking with a walker. By two weeks, most people can bend their knee to about 90 degrees. By six weeks, that increases to around 110 degrees, and many people have transitioned from a walker to a cane or no assistive device at all. Driving and light desk work typically resume between 6 and 12 weeks, depending on which knee was replaced and how quickly you regain control.
Risks and Complications
About 1 in 100 patients develops an infection around the new joint, according to the American Academy of Orthopaedic Surgeons. Infection can occur in the weeks after surgery or even years later when bacteria from another part of the body travel through the bloodstream. Signs include increasing pain, swelling, warmth, redness, or drainage from the incision. A superficial wound infection can often be treated with antibiotics, but a deep infection around the implant sometimes requires additional surgery to clean or replace the components.
Blood clots in the leg veins are another well-known risk, which is why you’ll be given blood-thinning medication after surgery and encouraged to move your feet and ankles frequently. Stiffness can develop if scar tissue limits your range of motion, a condition called arthrofibrosis, which occasionally requires a procedure to break up the scar tissue under anesthesia. Nerve or blood vessel injury, implant loosening, and fractures around the implant are possible but uncommon.
What the Implant Is Made Of
The metal parts of a knee replacement are most commonly made from cobalt-chromium alloy, a material that has been the standard since the 1980s because of its durability and smooth surface finish. Some newer femoral components use oxidized zirconium, a metal-ceramic hybrid that is harder and more scratch-resistant than cobalt-chromium, which may reduce wear on the plastic spacer over time. The plastic insert between the metal components is made from ultra-high-molecular-weight polyethylene, an extremely tough plastic engineered to withstand decades of repeated bending and weight-bearing. Modern versions of this plastic are cross-linked using radiation, which makes them more resistant to the gradual wear that was the main reason older implants eventually needed replacement.