What total knee replacement is
Total knee replacement is surgery for a knee worn out by arthritis, when the cartilage that lets the joint glide has broken down toward bare bone and the usual treatments no longer control the pain. It is one of the most common and reliable operations in orthopedics, with more than 700,000 performed in the United States each year. What it does best is relieve pain. Function improves as well, and the realistic goal is a knee that lets you get through a normal day, not one that feels twenty years old again.
The name overstates it. The knee is not removed, it is resurfaced, which is why the operation is also called total knee arthroplasty. Only the worn surfaces are replaced. A few millimeters of worn bone come off the end of the thighbone (femur) and the top of the shinbone (tibia), and usually the back of the kneecap, and those surfaces are capped with metal and a smooth plastic bearing. The ligaments and the bulk of your own bone stay where they are.
Who total knee replacement helps
Replacement is considered when several things line up: advanced arthritis on the X-ray, pain and stiffness that limit daily life, and non-surgical care that has been genuinely tried and is no longer enough. In practice, candidates usually have:
Severe pain that limits daily life
Knee pain that makes walking, stairs, or rising from a chair difficult, or that aches at rest, day or night.
Advanced arthritis on imaging
Cartilage worn through in more than one compartment of the knee on standing X-rays.
Non-surgical care no longer working
Anti-inflammatory medicine, physical therapy, weight loss, bracing, and injections have been tried and no longer hold the pain.
Deformity or instability
A leg that is bowing or turning knock-kneed, or a knee that buckles, meaning the joint is no longer doing its job.
There is no strict age or weight cutoff. Most people who have the operation are between 50 and 80, but the decision rests on how much the arthritis limits life and whether a person is healthy enough for surgery and rehabilitation, not on age alone. In younger patients the harder question is the implant: a replacement does not last forever, and the earlier it is done, the more likely a second operation will be needed later, which is a larger undertaking than the first. Carrying extra weight, diabetes, and smoking raise the risk of infection and slow healing, and are worth getting under control beforehand.
How the procedure is done
The operation takes about one to two hours. The surgeon removes the worn cartilage and a few millimeters of bone from the ends of the femur and tibia, then positions metal components that recreate the joint surface, fixed with bone cement or press-fit so bone grows into them. The back of the kneecap is often resurfaced with a plastic button, and a medical-grade plastic spacer is placed between the metal parts to give a smooth, low-friction bearing.
Seating the implant is the straightforward part. The exacting part is the balance: setting the soft tissues evenly and lining up the leg so the knee tracks smoothly through its full arc. This is tested with trial pieces, bending and straightening the knee and adjusting before anything is fixed for good.
Recovery after knee replacement
Most people are up on their feet with help the same day, using a walker, crutches, or a cane at first. The hospital stay is often a single night, and some replacements are done as outpatient surgery. The work of recovery is physical therapy, and pushing motion early matters: the knees that do best belong to the people who do their exercises.
Most people are managing their normal day within three to six weeks, with a knee that straightens fully and bends far enough for stairs and for getting in and out of a chair. Driving usually returns around four to six weeks, once the strong pain medicine is stopped and the leg can work the brake without hesitation. Pain with activity and at night is common for several weeks and settles with time.
Risks and complications
Like any operation, knee replacement carries risk, and the serious complications are uncommon. A deep infection that reaches the new joint occurs in fewer than 2 percent of people, and major medical events such as heart attack or stroke are rarer still. Risks discussed before surgery include:
- infection, including the rare deep infection around the implant (periprosthetic infection)
- a blood clot in the leg or lung, guarded against with blood thinners, early walking, and compression
- stiffness, occasionally enough to need the knee moved through its range under anesthesia
- a fracture in the bone around the implant
- wear or loosening of the components over the years, which can eventually call for further surgery
- lasting pain, which is uncommon; most people get significant pain relief
- rare injury to the nerves or blood vessels near the knee
Set against these risks is what advanced arthritis does when it is left alone: pain that no longer eases with rest, a knee that gives way, and a leg that slowly bends out of line. Surgery does not remove risk, it trades a problem that only worsens for one that can be fixed, which is why it is recommended when arthritis is end-stage and the better options are spent, and not before.
Outcomes and how long a knee replacement lasts
A replaced knee is built for a full, active life, just not a high-impact one. Walking, swimming, cycling, golf, light hiking, and dancing are all encouraged. Running and jumping are not, because the repeated pounding wears the plastic bearing faster. Kneeling is sometimes uncomfortable but not harmful, and some numbness of the skin around the incision is normal.
Modern implants are durable. More than 90 percent of total knee replacements are still working well 15 years after surgery. How long a given implant lasts depends more on how hard it is used, and on body weight, than on the calendar.
Frequently asked questions
Is the whole knee removed during a knee replacement?
No. The joint is resurfaced, not removed. A few millimeters of worn cartilage and bone come off the ends of the bones, metal and plastic surfaces are fitted, and the ligaments and most of your own bone stay in place. Only the worn surfaces are replaced.
How long does a knee replacement last?
More than 90 percent of modern total knee replacements are still functioning well 15 years after surgery. Longevity depends largely on activity level and body weight, since high-impact use and extra weight wear the plastic bearing faster.
When can I drive after knee replacement?
Usually around four to six weeks, once you are off the strong pain medicine and can brake hard in an emergency without hesitating. Recovery timing varies from person to person.
Am I too old for a knee replacement?
Age alone rarely rules it out. The decision rests on how much the arthritis limits daily life and whether you are healthy enough for surgery and rehabilitation. Knee replacement is performed successfully across a wide age range.
What activities are allowed after a knee replacement?
Low-impact activity is encouraged, including walking, swimming, cycling, golf, light hiking, and dancing. Running, jumping, and other high-impact activities are discouraged because the pounding wears the implant faster.
Further reading
For a fuller explanation, including candidacy, the operation, and recovery:
