Learn How Knee Replacement Surgery Works

What Knee Replacement Surgery Is and Why People Need It

Knee replacement surgery, also called knee arthroplasty, is a procedure where a surgeon removes damaged parts of your knee joint and replaces them with artificial parts made of metal and plastic. This surgery is one of the most common orthopedic procedures performed in the United States, with over 600,000 procedures done each year according to the Centers for Disease Control and Prevention.

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Your knee is a hinge joint where three bones meet: the femur (thighbone), tibia (shinbone), and patella (kneecap). The ends of these bones are covered with cartilage, a smooth tissue that allows bones to glide against each other without friction. When this cartilage wears away or gets damaged, the bones rub together, causing pain, stiffness, and swelling.

The most common reason people need knee replacement is osteoarthritis, a degenerative condition where cartilage gradually breaks down over time. About 10% of men and 13% of women over age 60 experience symptomatic knee osteoarthritis. Other reasons for knee replacement include rheumatoid arthritis, where the immune system attacks joint tissue; traumatic injuries from accidents or sports; and avascular necrosis, where bone tissue dies due to lack of blood supply.

Before recommending surgery, doctors typically try other treatments like physical therapy, weight management, medication, and injections. When these approaches no longer provide relief and daily activities become difficult, knee replacement may be considered. The goal of the surgery is to reduce pain and restore function so people can return to activities they enjoy.

Practical Takeaway: Understanding why your knee needs replacement helps you prepare mentally and physically for the procedure. Discuss with your doctor what specific knee damage or disease you have, as this affects how the surgery is performed and what results you might expect.

Types of Knee Replacement Procedures

There are three main types of knee replacement surgery, and your surgeon will recommend one based on which parts of your knee are damaged and your overall health. The type of procedure affects recovery time, how well your knee functions afterward, and how long the artificial joint lasts.

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Total knee replacement (TKR) is the most common type, accounting for about 90% of all knee replacement surgeries. In this procedure, the surgeon removes the damaged cartilage and bone from the femur, tibia, and patella, then attaches artificial components to each bone. The artificial knee has a metal femoral component that slides on a plastic spacer attached to the tibia, and the patella is also resurfaced with plastic. The surgery typically takes 1 to 2 hours and requires a hospital stay of 1 to 3 days, though some patients go home the same day. Research shows that 90% of total knee replacements are still functioning well after 10 years.

Partial knee replacement (PKR), also called unicompartmental knee replacement, is used when only one side of the knee is damaged while the other compartments are healthy. Surgeons remove only the damaged cartilage and bone and replace it with a smaller artificial component. This procedure is less invasive than total knee replacement, with a smaller incision, less bone removal, and faster recovery. However, only about 10% of people with knee arthritis are candidates for this procedure because it requires very specific patterns of damage. Studies show that partial knee replacements function for about 15 to 20 years in many patients.

Revision knee replacement is performed when a previous artificial knee needs to be replaced, typically because the original implant has worn out, loosened, or become infected. This is a more complex surgery than the first replacement because the surgeon must remove the old components, which may have bonded to the bone, and then install new ones. The surgery takes longer and requires more bone preparation. About 10% of patients eventually need revision surgery, though modern implants are lasting longer than earlier versions.

Practical Takeaway: Ask your surgeon which type of knee replacement you are having and why that procedure is right for your specific knee damage. Understanding the differences helps you set realistic expectations for recovery and long-term function.

The Surgical Procedure: What Happens During Surgery

Understanding the step-by-step process of knee replacement surgery can reduce anxiety and help you know what to expect. While the exact technique varies slightly between surgeons, the basic steps follow a consistent pattern.

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The procedure begins with anesthesia. Most patients receive regional anesthesia, where medication numbs everything below the waist while the patient remains awake or lightly sedated. Some patients receive general anesthesia where they are put to sleep. Your anesthesiologist will discuss which option is best for you based on your health history, age, and personal preferences.

Once anesthesia takes effect, the surgeon makes an incision, typically 8 to 10 inches long, down the front of the knee. This allows access to the knee joint. Some surgeons use minimally invasive techniques with smaller incisions of 4 to 6 inches, which may reduce pain and speed recovery, though the long-term results are similar. The surgeon then carefully moves the kneecap to the side to view the knee joint.

The damaged cartilage and bone are then removed in a precise sequence. Using specialized cutting guides and instruments, the surgeon removes the damaged surfaces from the femur, creating a flat surface. Next, the damaged tibia surface is cut. These cuts are made at specific angles to ensure proper alignment of the artificial knee. The patella is assessed and resurfaced if necessary, though some surgeons leave it in place if it is not significantly damaged.

After removing the damaged bone and cartilage, the surgeon places the metal femoral component on the end of the thighbone, securing it with special cement or by allowing bone to grow into it. The plastic spacer is then attached to the tibia. These components are aligned carefully to match your leg's natural alignment, which is critical for proper function and longevity of the implant. The surgeon tests the knee's motion and stability to ensure proper fit and function.

Once everything is positioned correctly, the surgeon closes the incision with stitches or staples. The entire surgical procedure typically takes 1 to 2 hours. Most patients go to a recovery room where they wake from anesthesia and begin pain management. Many modern surgical centers use a rapid recovery protocol that gets patients moving and going home the same day or after one night in the hospital.

Practical Takeaway: Knowing the surgical steps helps demystify the procedure. Ask your surgeon if they use any special techniques like computer-assisted navigation or minimally invasive approaches, as these may affect your recovery timeline.

Recovery Timeline: What to Expect After Surgery

Recovery from knee replacement involves several phases, and knowing what happens at each stage helps you prepare and manage expectations. Recovery is not the same for everyone, but most patients follow a general timeline.

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Immediate Recovery (First 24 Hours): Right after surgery, you will be in a recovery room where nurses monitor your vital signs and pain levels. A catheter may be placed to help with urination while you cannot get out of bed. Most patients experience significant pain and swelling immediately after surgery. Your medical team will manage this with medications, ice, and elevation. Physical therapy typically begins within hours of surgery, with a therapist helping you do gentle movement exercises or walk with assistance. This early movement prevents blood clots, maintains circulation, and begins rebuilding strength.

Hospital and Early Home Recovery (1 to 6 Weeks): Most patients go home within 1 to 3 days after surgery. During this period, swelling and pain gradually decrease, though both may be significant. You will need crutches or a walker and cannot put full weight on the surgical leg for the first few weeks. Physical therapy becomes more intensive, with sessions focused on regaining range of motion and building strength. Many patients work with a physical therapist 2 to 3 times per week. Pain management involves medications prescribed by your doctor, and you may continue taking pain relievers for 2 to 6 weeks. You cannot drive while taking narcotic pain medications.

Intermediate Recovery (6 Weeks to 3 Months): By 6 weeks, most patients can walk without assistive devices, though they may still have a slight limp. Swelling continues to decrease. Range of motion gradually improves as you work with your physical therapist and do home exercises. Most patients can return