A knee revision is a second surgery to replace a knee implant that has worn out, loosened, or failed. It’s more complex than the original knee replacement because the surgeon must first remove the existing implant, address any bone loss that has occurred, and then fit a new prosthesis into a joint that has already been operated on once. Nearly 79,000 knee revisions were performed in the U.S. in 2022, up from about 53,000 in 2013, and that number is projected to reach over 227,000 by 2040 as more people live longer with knee replacements.
Why a Knee Replacement Might Need Replacing
Most first-time knee replacements last well over a decade. Studies of well-established implant designs show 10-year survival rates above 92%, with some designs reaching 95% or higher. But implants aren’t permanent, and several problems can eventually require a revision.
The most common reason is wear and loosening, which accounts for roughly 47% of revision cases. Over years of use, the plastic liner between the metal components gradually wears down. Tiny particles shed from this liner trigger an immune response that eats away at the surrounding bone, a process called osteolysis. As the bone weakens, the implant loses its anchor and begins to shift. You might notice increasing pain, a change in leg alignment, or a feeling that the knee isn’t stable.
Infection is the second major cause. It can develop shortly after surgery or appear years later when bacteria from elsewhere in the body settle on the implant. Even when the implant itself is still firmly in place, infection causes persistent pain, swelling, and sometimes drainage from the joint that won’t resolve without surgery. Many infections aren’t obvious: the classic signs of fever, redness, and chills don’t always show up, which is why blood tests and fluid samples drawn from the joint are often needed to confirm the diagnosis.
Instability, where the knee feels like it’s giving way during activity, is another trigger. This happens when the ligaments or soft tissues around the joint can no longer keep the implant properly aligned. Fractures around the implant (called periprosthetic fractures) and severe stiffness that limits range of motion round out the most common reasons for revision.
How Doctors Determine You Need One
If your replaced knee starts causing persistent pain, swelling, or instability, your doctor will typically start with X-rays to check whether the implant has shifted or whether bone around it is deteriorating. MRI scans can reveal problems that X-rays miss, including soft tissue damage, bone marrow changes, early loosening, and signs of infection. MRI is especially useful because it can show the full picture: bone resorption around the implant, fractures, scar tissue buildup, and even abnormal blood vessel activity that might explain unexplained bleeding in the joint.
When infection is suspected, drawing fluid from the joint with a needle is often the definitive test. This aspiration identifies both whether infection is present and which specific bacteria are involved, which determines how it will be treated.
What Happens During the Surgery
Revision surgery is substantially more involved than a first-time knee replacement. The surgeon reopens the existing scar and carefully removes each component of the old implant in a specific order: first the plastic insert, then the thighbone piece, the shinbone piece, and finally the kneecap component. This removal process is delicate and sometimes time-consuming. Well-fixed cemented implants can be particularly difficult to extract, requiring specialized cutting tools, ultrasonic instruments, and thin flexible saws to separate the implant from bone without causing further damage.
Once the old hardware is out, the surgeon evaluates how much bone has been lost. This is the central challenge of revision surgery. Years of wear, loosening, or infection often leave gaps and defects in the bone that weren’t there during the original procedure. Small defects can be filled with cement or bone graft. Larger defects require metal augments, wedges, or specialized cone-shaped devices that slot into the hollowed-out bone to recreate a stable foundation. When significant bone is missing, longer stems on the new implant extend deeper into the bone shaft to find solid anchoring points.
About 25% of revision patients need additional soft tissue work during the procedure to properly align the kneecap, compared to only about 3% during first-time replacements. The kneecap surface is usually replaced during revision unless there isn’t enough bone left to support it.
Revision Implants Are Different
The implants used in revision surgery are not the same ones used in a first-time replacement. They come in a range of designs that offer increasing levels of built-in stability, chosen based on how much bone and ligament support remains.
When the ligaments around the knee are still functional, a relatively simple implant with a post-and-cam mechanism can substitute for ligament function and keep the joint stable during bending. When the ligaments on the sides of the knee are damaged or absent, a more constrained design is used. These have a deeper housing and a taller, broader post that locks into it, physically limiting the joint from wobbling side to side or rotating too far.
In the most severe cases, where bone loss and soft tissue damage are extensive, a hinged implant mechanically links the thighbone and shinbone components together. Modern versions allow some rotation within the hinge, which reduces the stress transferred to the bone and lowers the risk of the new implant loosening over time.
Risks Compared to First-Time Replacement
Revision surgery carries higher risks than the original procedure across the board. A large meta-analysis found that patients undergoing revision face a 45% higher rate of the new implant loosening again, a 36% higher risk of infection, a 73% higher rate of stiffness, and a 21% higher likelihood of persistent knee pain. These elevated risks stem from the fact that revision operates on compromised territory: less bone stock, more scar tissue, and a blood supply that’s already been disrupted by the first surgery.
Bone fracture during the operation itself is another risk specific to revision. The process of removing a well-fixed implant can crack weakened bone, which may change the reconstruction plan on the spot and extend recovery time.
Recovery Takes Longer
Recovery from a knee revision is less predictable than recovery from a first-time replacement. Most people are encouraged to stand and walk with a walker or crutches on the same day or the day after surgery. The first one to two weeks are typically the most painful. At the two-week mark, you’ll see your surgeon to check how the incision is healing, and physical therapy usually begins around that time.
Most people feel comfortable returning to work and resuming lighter daily activities somewhere between three and six months after surgery, though strenuous exercise and high-impact activities take longer. Full recovery can take up to 12 months, and the timeline varies considerably from person to person depending on the extent of bone reconstruction, the type of implant used, and overall health going into surgery.
Who Gets Knee Revisions
The average age at revision is about 70, with patients ranging from 40 to 86 years old. This age has remained relatively stable over time, even as knee replacements are increasingly performed on younger, more active patients. Because younger patients put more years and more physical demand on their implants, orthopedic surgeons expect the volume of revision surgeries to continue climbing. The projected annual growth rate of 5.7% through 2040 reflects both an aging population and the expanding pool of people living with knee replacements that will eventually wear out.