There are several types of knee replacement surgery, and the right one depends on how much of your knee is damaged. The three main categories are total knee replacement, partial knee replacement, and revision knee replacement. Within each, the specific implant materials, design, and surgical technique can vary further.
Total Knee Replacement
Total knee replacement is the most common version. It resurfaces all three compartments of the knee: the inside (medial), the outside (lateral), and the front between the kneecap and thighbone (patellofemoral). The surgeon removes damaged cartilage and bone from each surface, then caps them with metal components that recreate the joint. A medical-grade plastic spacer sits between the metal pieces, creating a smooth gliding surface. In many cases, the underside of the kneecap is also resurfaced with a plastic button, though some surgeons skip this step depending on the patient.
Total knee replacement is typically recommended when arthritis or damage affects most or all of the joint, and when pain limits everyday activities like walking, climbing stairs, or getting out of a chair. It’s also considered when other treatments, including injections, physical therapy, and medications, haven’t provided enough relief. About 90% of total knee replacements are still functioning at 20 years, and over 82% last 25 years, based on large registry data from Finland and Australia covering hundreds of thousands of patients. In a modern cohort of patients, nearly 90% reported satisfaction after the procedure.
Partial (Unicompartmental) Knee Replacement
If arthritis is confined to just one compartment of your knee, a partial replacement may be an option. This procedure resurfaces only the damaged section while leaving the healthy bone, cartilage, and ligaments intact. Most commonly, it addresses the medial (inner) compartment, since that’s where wear tends to concentrate, but it can also be done on the lateral (outer) side.
Not everyone qualifies. You need intact ligaments, good range of motion, and damage that’s clearly limited to one compartment. Inflammatory arthritis (like rheumatoid arthritis), significant knee stiffness, or ligament damage will usually rule out this option. When it is appropriate, partial replacement offers a smaller incision, less disruption to surrounding tissue, and a recovery that’s generally faster than a total replacement. The tradeoff: if arthritis later develops in the remaining compartments, you may eventually need a total knee replacement.
Patellofemoral Replacement
This is a less common type of partial replacement that specifically addresses the front of the knee, the space between the kneecap and the thighbone. Candidates typically have pain only behind the kneecap, and X-rays from multiple angles must confirm that arthritis hasn’t spread to the rest of the joint.
The exclusion list is longer than for other partial replacements. Poor kneecap tracking (where the kneecap shifts out of place during bending), major leg deformity, inflammatory arthritis, gout, morbid obesity, ligament damage, or significant stiffness can all disqualify you. When it does work, patients often report that the knee feels more natural than after a total replacement, because the healthy portions of the joint remain untouched. Recovery tends to be quicker for the same reason: less tissue is disturbed during surgery.
Revision Knee Replacement
Revision surgery replaces some or all of the components from a previous knee replacement. It’s a more complex procedure than the original surgery and is needed when the first implant wears out, loosens, or fails for another reason.
The most common cause is implant loosening over time. Tiny particles that wear off the plastic spacer can trigger an immune response that gradually weakens the surrounding bone, a process called osteolysis. High-impact activities and excess body weight accelerate this wear. Other reasons for revision include infection (which causes pain, swelling, and sometimes drainage), instability from damaged or poorly balanced ligaments, excessive scar tissue that limits motion, and fractures around the implant from a fall.
Because bone loss is common by the time revision is needed, surgeons often use specialized implants with longer, thicker stems that anchor deeper into the bone. Metal blocks or platforms may be added to compensate for missing bone. Recovery from revision surgery is generally longer and more involved than the original procedure.
Implant Materials
Regardless of the type of replacement, your implant will be made from one of four material combinations, each with different strengths.
- Metal on plastic is the most widely used. A cobalt-chromium, titanium, zirconium, or nickel metal piece rides on a polyethylene plastic spacer. It’s the least expensive option and has the longest safety track record.
- Ceramic on plastic swaps the metal thighbone component for ceramic, or coats it in ceramic. This is a good option for people with nickel sensitivity.
- Ceramic on ceramic uses ceramic on both sides of the joint. These components are the least likely to provoke a reaction in the body.
- Metal on metal uses metal on both sides. Originally developed to provide longer-lasting joints for younger, active patients, these are now considered mainly for young, active men because of concerns about metal particle release.
Custom-Fit Implants
Standard implants come in preset sizes. Custom implants are designed from a CT scan of your specific knee. Algorithms convert the scan into a 3D model, mapping bone contours and correcting areas distorted by disease. The resulting implant is often asymmetrical, with different dimensions on the inner and outer sides, mimicking the natural variation of your anatomy.
The functional advantage is that a custom implant can work more naturally with your existing ligaments and tendons. A study published in the Journal of Arthroplasty found that during activities like stair climbing and squatting, customized implants moved more like a natural knee compared to conventional ones. With off-the-shelf implants, surgeons have to make compromises to get the soft tissues to work with a component that isn’t the same shape as your original bone. The downsides: custom implants cost more, and the design and manufacturing process takes about six weeks, whereas standard implants are available immediately.
Robotic-Assisted Surgery
Robotic-assisted knee replacement isn’t a different type of implant. It’s a different way of performing the surgery. The surgeon uses a robotic arm to guide bone cuts with greater precision. This can help with ligament balancing during the procedure. However, current evidence hasn’t shown a clear advantage in long-term outcomes compared to manual techniques. Cleveland Clinic has described the comparison as essentially “a tie” for now. The technology is still evolving, and its greatest value may emerge as longer-term data accumulates.
What Recovery Looks Like
Full recovery from any knee replacement takes about a year, but most people return to their usual daily activities within six weeks. You’ll work with a physical therapist for up to a few months after surgery, focusing on safely bending your knee and rebuilding walking ability. Your timeline will depend on your age, activity level before surgery, and any other health conditions.
Partial replacements generally involve shorter recovery periods than total replacements because less tissue is cut and less bone is resurfaced. Revision surgery sits at the other end of the spectrum, often requiring a longer and more demanding rehabilitation because of the complexity of the procedure and any bone loss that needed to be addressed.