Understanding Knee Replacement Surgery: What It Is and Why People Need It
Knee replacement surgery, also called knee arthroplasty, is a procedure where a surgeon removes damaged parts of the knee joint and replaces them with artificial parts made of metal, plastic, or ceramic materials. The procedure involves replacing the surfaces of the bones in the knee joint where they meet. Doctors perform this surgery when the knee joint has become severely damaged and other treatments have not worked well enough to restore function and reduce pain.
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The knee is one of the body's largest and most complex joints. It connects the thighbone (femur) to the shinbone (tibia) and includes cartilage, ligaments, tendons, and fluid that help the joint move smoothly. When this cartilage wears down over time or gets damaged through injury, the bones can rub directly against each other, causing pain, stiffness, and reduced movement. This condition is most commonly caused by osteoarthritis, a degenerative joint disease where protective cartilage gradually breaks down.
According to the American Academy of Orthopaedic Surgeons, approximately 790,000 knee replacement procedures are performed in the United States each year. The surgery has been performed since the 1960s, with modern techniques and materials constantly improving outcomes and longevity. Studies show that about 90% of knee replacements function well 10 years after surgery, and many last 15 to 20 years or longer.
Beyond osteoarthritis, other reasons people may need knee replacement include rheumatoid arthritis (an autoimmune disease affecting joints), traumatic injuries that severely damage the knee, and knee deformities that affect function. Some people develop severe knee problems from previous injuries that occurred years or decades earlier.
Practical takeaway: Understanding that knee replacement is a well-established procedure with decades of surgical refinement and strong success rates may help people discuss this option with their healthcare provider if they experience persistent knee problems.
Age Considerations: How Age Affects Knee Replacement Surgery
Age is an important factor that doctors consider when discussing knee replacement, but it is not a barrier to having the procedure. People of many different ages undergo successful knee replacement surgery. The National Institutes of Health reports that while most knee replacements occur in people aged 50 to 80, younger and older patients can be good candidates depending on their overall health status and specific medical circumstances.
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Younger patients—typically those under 50—may hesitate to have knee replacement because artificial knees have a limited lifespan. Current artificial knee joints typically last 15 to 25 years, depending on the person's activity level and other factors. A younger person undergoing surgery might eventually need a revision surgery (a second procedure to replace or repair the artificial joint). However, younger patients may benefit from knee replacement if they have severe pain and dysfunction that significantly limits their quality of life and daily activities. Many younger patients find that the years of improved function and reduced pain make the procedure worthwhile, even if revision surgery may be needed later.
Older patients—typically those over 70—may worry about surgery risks related to age. However, age alone is not a reason to avoid surgery. What matters more is overall health. Many people in their 70s, 80s, and even 90s have had successful knee replacements. Factors such as heart and lung function, blood pressure control, blood sugar management (especially for diabetes), and mental alertness are often more important than the number of years a person has lived. A thorough medical evaluation before surgery helps determine whether an older person can safely undergo the procedure.
Studies show that older patients who undergo knee replacement often experience significant improvements in pain, function, and quality of life. One study in the journal Arthritis Care & Research found that patients aged 75 and older who had knee replacement reported reduced pain and improved ability to perform daily activities, with outcomes comparable to younger patients.
Pre-surgery medical testing may be needed for all age groups but is especially common for older patients or those with medical conditions like heart disease, diabetes, or high blood pressure. These tests help surgeons understand a person's overall health and prepare for any special considerations during surgery.
Practical takeaway: Age is just one factor in determining whether someone should have knee replacement. A conversation with an orthopedic surgeon about overall health, activity goals, and personal preferences is more informative than age alone.
Medical Evaluation and Preparation Before Surgery
Before knee replacement surgery can be scheduled, patients undergo a thorough medical evaluation. This process involves multiple appointments and tests to ensure the person is healthy enough for surgery and to identify any conditions that need to be managed before or after the procedure. The evaluation typically includes a detailed medical history, physical examination, imaging studies, and blood tests.
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Imaging studies are crucial for surgical planning. An X-ray shows the extent of knee damage and helps the surgeon determine which type of artificial joint components will work best. Sometimes a magnetic resonance imaging (MRI) scan is ordered to get a more detailed view of soft tissues like ligaments and cartilage. Computed tomography (CT) scans may be used in complex cases to help plan the exact positioning of artificial components.
Blood tests check for conditions that could affect surgery safety or recovery. These tests measure blood cell counts, kidney and liver function, blood sugar levels, and blood clotting ability. Patients with diabetes need particular attention because high blood sugar can slow wound healing and increase infection risk. Similarly, blood pressure must be controlled, and heart function may need to be evaluated, especially for older patients or those with cardiac history.
Patients should discuss all medications they take during the pre-surgery evaluation. Some medications need to be stopped before surgery—particularly blood thinners like warfarin or aspirin taken for heart problems—because they increase bleeding risk during the procedure. Other medications may need to be adjusted. Patients should never stop taking medications without medical guidance, as sudden changes can be dangerous.
Physical therapy often begins before surgery. Pre-operative physical therapy helps strengthen the muscles around the knee and improves flexibility, which can lead to better outcomes after surgery. A physical therapist teaches exercises that patients can do at home to prepare their legs for the demands of post-operative rehabilitation.
Patients also meet with anesthesia specialists who discuss which type of anesthesia will be used. Most knee replacement surgeries use regional anesthesia (numbing the leg), general anesthesia (putting the person to sleep), or a combination. The anesthesia team evaluates whether any special precautions are needed based on the patient's medical history.
Practical takeaway: Thorough pre-operative evaluation helps identify and manage health conditions, making surgery safer and supporting better recovery outcomes.
The Surgical Procedure: What Happens During Knee Replacement
Modern knee replacement surgery typically takes 60 to 90 minutes, though the exact time varies based on the complexity of the case and the surgeon's experience. Understanding what happens during surgery can reduce anxiety and help patients know what to expect during recovery.
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The surgeon begins by making an incision, typically 8 to 12 inches long, over the front of the knee. This incision allows access to the knee joint while minimizing damage to surrounding structures. Some surgeons now use minimally invasive techniques that use smaller incisions, though the benefit of these approaches compared to standard surgery remains debated among orthopedic specialists.
Once the joint is exposed, the surgeon removes the damaged cartilage and bone from the ends of the femur and tibia. Special cutting guides and instruments help ensure precise removal and proper alignment of the artificial components. The surgeon then tests the fit and alignment of the artificial components before cementing or pressing them into place. Most modern artificial knees use cement to secure the components, though some newer designs can be pressed into bone without cement.
The artificial knee joint typically consists of three main components: a metal cap that covers the end of the femur, a metal and plastic spacer that sits on the tibia, and sometimes a plastic component that replaces the underside of the kneecap. This design allows the joint to move smoothly while bearing the body's weight.
During surgery, the surgeon carefully balances the soft tissues—muscles, ligaments, and tendons—around the knee. Proper balance helps ensure that the new joint moves correctly and remains stable. Once the artificial components are in place and properly balanced, the surgeon closes the incision with stitches or staples and applies a sterile dressing.
Most patients receive pain-relieving medications during surgery and recovery. Local anesthetics are often injected