Do I need a partial or total knee replacement?

One of the most common concerns I hear about partial knee replacement is that the rest of the knee will eventually wear out, making another operation inevitable.

That is an understandable worry. If you are going through surgery, you want it to last. But leaving a healthy compartment in place does not mean it is destined to need replacement. Long-term studies show that a partial can be a durable operation for an appropriately selected knee.

There is another part of this conversation that matters to patients: how the knee will feel afterward. Pain relief and a knee that feels natural are different outcomes. Both belong in the decision.

Will the other side of my knee eventually wear out?

Arthritis can progress in a compartment that was preserved. It is one possible reason for converting a partial to a total knee replacement later. Possible does not mean inevitable.

The TOPKAT randomized trial followed 528 people with arthritis in the inner compartment who were suitable for partial replacement. They were assigned to a partial or total replacement. At ten years, the investigators reported similar pain-and-function scores, reoperation rates and revision rates. Most knees in either group had not required revision.

That is reassuring evidence for someone who is a candidate. It does not mean the risk is identical for every patient. The trial involved surgeons with relevant procedural expertise, and 73% of those eligible for the main ten-year assessment responded, after excluding people who had died or withdrawn. Its findings also concern inner-compartment arthritis, not every pattern of knee disease.

The condition of the knee you have today is central to choosing an operation that can serve you well over time.

What is the difference?

The knee has three compartments: the inner side, the outer side, and the area behind the kneecap. Arthritis does not necessarily affect all three to the same degree.

A partial knee replacement resurfaces a damaged compartment while preserving the unaffected areas and supporting ligaments. You may hear it called a “half knee replacement,” although “partial” describes it more accurately.

A total knee replacement resurfaces the ends of the thighbone and shinbone across the knee. The undersurface of the kneecap may also be resurfaced. The surgeon keeps the leg and much of the surrounding tissue; “total” refers to the replacement of the joint surfaces.

This article mainly discusses replacement of the inner or outer compartment. Replacement limited to the joint behind the kneecap is a separate procedure with its own selection considerations.

How do we know whether a partial will fit?

The evaluation needs to establish that the compartment being considered is responsible for the symptoms and that the remaining knee can support the plan.

Your surgeon reviews where the pain is, how the knee moves, its alignment and ligament stability, and the pattern on the X-rays. Significant stiffness, ligament problems, inflammatory arthritis, or substantial disease elsewhere can change the recommendation. AAOS patient guidance describes these considerations.

A useful way to discuss the images is to ask the surgeon to point out the damaged area and explain the condition of the areas that would remain. Knowing that arthritis is present is only the beginning of the decision.

Will a partial knee feel more normal?

This is something I discuss with patients because pain relief does not tell us everything about life after surgery. A knee can hurt less while you remain aware that it has been replaced.

A 2025 systematic review of 19 studies involving 4,500 knees compared partial and total replacement using the Forgotten Joint Score. This questionnaire measures awareness of the joint during everyday activities. On average, people with partial replacements reported less awareness of their replaced knee.

That supports the possibility of a more natural-feeling knee after a partial. Most included studies were observational, results varied considerably, and the authors detected publication bias. We cannot promise that every partial will feel normal or that every total will feel artificial.

I want patients to consider how the knee may feel alongside pain relief, function and the chance of future surgery.

What about recovery?

A systematic review in The BMJ found shorter hospital stays after partial replacement across different types of studies. Some functional outcomes favored partial replacement in nonrandomized studies, and cohort studies reported an earlier return to work or sport. Pain outcomes did not show a clear difference.

People receiving the two operations outside a trial may differ in ways that affect recovery. The studies also span different hospital practices, so their hospital-stay figures should not be treated as a prediction for today’s outpatient care.

Ask what recovery is likely to involve for your knee, your work and the activities you hope to return to.

Why do some reports show more repeat surgery after partial replacement?

A revision is another operation to remove, replace or change implant components. It is one type of repeat surgery; studies may count other procedures separately. Both partial and total replacements can eventually require revision.

A 2024 meta-analysis of clinical studies and joint registries found higher overall revision rates after partial replacement. Those broader findings belong in the discussion alongside TOPKAT.

Registries capture a broad range of surgeons, patients and implants. The review discusses differences in surgical experience and the threshold for recommending revision as possible contributors. These factors help explain why a national average and a trial may differ; they do not establish that the revision risk disappears with an experienced surgeon.

A total replacement also carries a risk of future surgery. Problems such as infection or implant loosening can affect either operation. A useful estimate needs to specify the operation being counted, the follow-up period and the patients studied.

The useful question is: “How do you assess the chance of another operation for someone with my knee, and what would that operation involve?”

What should I ask at the consultation?

• Which parts of my knee are damaged, and which are reasonably preserved?
• Am I a candidate for a partial replacement? What findings support or rule out that option?
• How regularly do you perform partial knee replacement, including the type you are recommending?
• What differences in recovery, function and future surgery should matter most to me?
• If you recommend a total replacement, what about my knee leads you to that choice?

I want patients to understand the reason for the recommendation. When a partial fits, it should be part of the discussion. When a total fits better, the explanation should be specific to the knee in front of us.