Types of Knee Replacement: Total, Partial and Kneecap

There are three main types of knee replacement, matched to how much of the joint is worn: total, partial (unicompartmental), and kneecap (patellofemoral). A total knee replacement resurfaces all three compartments of the knee with metal and plastic components; a partial resurfaces only the one damaged compartment, keeping the healthy bone and ligaments; and a kneecap replacement resurfaces only the joint behind the patella¹. Total is the most common; the right choice depends on your pattern of wear, not on one type being best.

When I was choosing, I assumed “knee replacement” meant one operation. It does not, and understanding the types helped me ask my surgeon better questions. This guide, checked by a consultant orthopaedic surgeon, walks through each type, what the implant is made of, and how the choice is made. For the full picture of the operation itself, see our pillar guide to knee replacement surgery.

Total knee replacement

A total knee replacement resurfaces all three compartments of the knee with metal and plastic, and it is the most common type. The surgeon caps the worn ends of the thigh bone and shin bone with metal, places a polyethylene plastic spacer between them, and often resurfaces the back of the kneecap too. It suits the many people whose arthritis is widespread rather than confined to one side. Surgery takes about 1 to 2 hours and the hospital stay is 1 to 3 days². I had a total replacement, and the predictability of it was part of why my surgeon recommended it over a partial.

Partial (unicompartmental) knee replacement

A partial knee replacement resurfaces only the one damaged compartment of the knee, usually the inner (medial) side, keeping the healthy bone and ligaments intact³. Because less of the knee is disturbed, recovery is often quicker and the knee can feel more natural. The trade-off is that it only works when wear is confined to one compartment, and it carries a slightly higher chance of needing a later revision if arthritis spreads to the rest of the knee. We set out who suits each in partial vs total knee replacement.

Kneecap (patellofemoral) replacement

A kneecap replacement resurfaces only the joint behind the kneecap, and it is the least common partial option. It is considered when arthritis is isolated to the patellofemoral compartment, the surface where the kneecap glides over the thigh bone, with the rest of the knee healthy. It is a smaller operation than a total replacement, but it is used selectively because isolated kneecap arthritis is uncommon and the results are less predictable than a total in widespread disease.

What knee implants are made of

Knee implants are made of metal with a plastic spacer. The metal parts are commonly cobalt-chromium and titanium, chosen for strength and to resist wear; between them sits a medical-grade polyethylene plastic spacer that the metal surfaces glide against, doing the job your worn cartilage used to do. The implant may be fixed to the bone with bone cement, or designed so your bone grows onto it (uncemented). Your surgeon chooses based on your bone quality, age, and activity level. The plastic spacer is the part most likely to wear over decades, which is one reason an implant can eventually need a revision knee replacement.

How long does each type last?

Across the main types, around 90 to 95% of implants are still in place at 10 years, and they typically last 15 to 20+ years⁴. Longevity depends more on your age, weight, and activity level than on the type itself. Partial replacements have a slightly higher chance of needing later revision because arthritis can spread to the compartments that were left alone. Younger and more active patients wear any implant faster.

How is the type chosen for you?

Your surgeon chooses the type by looking at how much of the joint is worn, your leg alignment, the state of your ligaments, your age, and your bone quality. Widespread arthritis across the knee points to a total replacement; wear confined to one compartment may suit a partial; isolated kneecap wear may suit a patellofemoral replacement. This is a decision to make together with your surgical team, who can examine you and read your X-rays. If you are still working out whether you need surgery at all, start with signs you need a knee replacement and alternatives to knee replacement.