A knee replacement is a surgery that removes damaged bone and cartilage from your knee joint and replaces them with artificial parts made of metal and plastic. The goal is straightforward: relieve pain and restore movement when other treatments have stopped working. It’s one of the most common orthopedic surgeries performed worldwide, and roughly 82% of total knee replacements are still functioning 25 years later.
What Happens During the Surgery
The surgeon makes a cut down the front of your knee and moves the kneecap to the side to access the joint behind it. From there, they cut away the damaged ends of your thighbone and shinbone. New components are fitted over the reshaped ends of both bones, creating a new joint surface. A smooth plastic spacer sits between the metal parts, allowing the joint to glide the way healthy cartilage once did.
The metal pieces are typically made from titanium or cobalt-chromium alloys, chosen because the body tolerates them well and they hold up under decades of use. The plastic spacer is made from an ultra-high-molecular-weight polyethylene, an extremely durable material specifically engineered to handle the repetitive stress of walking, bending, and climbing stairs. Together, these components mimic the shape and movement of a natural knee.
Most procedures take one to two hours under general or spinal anesthesia. Some surgeons now use robotic-assisted systems that create a 3D plan of your knee before surgery and provide real-time guidance during the procedure. In one large comparison, 95% of patients who had robotic-assisted surgery reported being satisfied or very satisfied, compared to 87% with the conventional approach. Both methods are considered safe and effective.
Total vs. Partial Knee Replacement
Your knee has three compartments: the inside (medial), the outside (lateral), and the area behind the kneecap (patellofemoral). In a total knee replacement, two or three of these surfaces are resurfaced. In a partial knee replacement, only the single damaged compartment gets new parts, leaving the healthy portions of the joint untouched.
Only a small percentage of patients qualify for a partial replacement, because most people have damage in more than one area by the time surgery becomes necessary. When it is an option, partial replacement preserves more of your natural bone and ligaments, which can make the knee feel more natural afterward. The tradeoff is longevity: about 70% of partial replacements last 25 years, compared to 82% for total replacements, according to a large meta-analysis published in The Lancet.
Who Needs a Knee Replacement
Surgery is typically considered after non-surgical options have been exhausted. That includes anti-inflammatory medications, cortisone or lubricating injections, physical therapy, bracing, and weight management. According to the American Academy of Orthopaedic Surgeons, recommendations are based on pain and disability, not age.
Common signs that you may be a candidate include:
- Pain that limits daily activities like walking more than a few blocks, climbing stairs, or getting in and out of chairs
- Chronic swelling and inflammation that doesn’t improve with rest or medication
- Knee deformity such as visible bowing inward or outward
- Dependence on a cane or walker due to knee instability or pain
- Failure of other treatments to provide meaningful relief
What Recovery Looks Like
Recovery starts the same day as surgery. You’ll begin simple exercises in the recovery room, starting with ankle pumps to keep blood flowing. Within the first day or two, a physical therapist will help you stand and take your first steps with a walker.
The early weeks are the most intensive period for rehabilitation. Most surgeons and physical therapists recommend exercising 20 to 30 minutes daily, sometimes two to three times a day, along with walking for 30 minutes two to three times daily. Early exercises focus on straightening the knee fully and gradually increasing how far you can bend it. You’ll do things like tightening your thigh muscles while lying down, performing straight leg raises, and practicing supported knee bends.
Around four to six weeks after surgery, you can typically start using a stationary bike for 10 to 15 minutes at a time, building up to 20 to 30 minutes several times a week. Resistance exercises with light weights usually begin in this same window. Driving is generally possible four to six weeks after a right knee replacement. If your left knee was replaced and you drive an automatic, you may be back behind the wheel in two to three weeks.
Most people notice significant pain improvement within the first three months. Full recovery, meaning the point where the knee feels strong and natural in daily life, usually takes six months to a year. The knee will continue to improve subtly beyond that.
Risks and Complications
Knee replacement is a safe procedure overall, but like any major surgery, it carries risks. A large study tracking more than 150,000 knee replacements found the following complication rates within the first year:
- Blood clots (deep vein thrombosis): occurred in about 0.6% of patients, typically within the first one to two weeks
- Joint infection: occurred in about 0.5% of patients, often appearing around two months after surgery
- Revision surgery (for any reason): needed in about 0.5% of patients within the first year
To reduce the risk of blood clots, you’ll be given blood-thinning medication and encouraged to move your feet and ankles frequently starting immediately after surgery. Infection prevention includes antibiotics given before and after the procedure, along with careful wound care at home. Signs to watch for include increasing redness, warmth, or drainage at the incision site, persistent fever, or sudden new swelling in the calf.
How Long a Knee Replacement Lasts
Modern implants are remarkably durable. Pooled data from 14 national joint registries shows that approximately 82% of total knee replacements survive 25 years without needing revision. That means the majority of people who get a knee replacement in their 60s or 70s will never need a second surgery on that knee.
Younger, more active patients do face a higher likelihood of eventually wearing out the implant simply because they’ll put more years and more miles on it. Maintaining a healthy weight, staying active without high-impact sports, and following through with rehabilitation all help extend the life of the replacement. Activities like swimming, cycling, walking, and golf are generally well tolerated. Running and jumping sports put more stress on the components and are typically discouraged.