How long will my knee replacement last?

The question that comes up in almost every consultation

It is rare to have a knee replacement consultation where longevity is not discussed. Patients want to know whether they are likely to need a second operation, and if so, when. It is a completely reasonable concern — knee replacement is a significant undertaking and people want to go into it with realistic expectations.

The best data we have to answer this question comes from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), a national database that has been tracking every joint replacement performed in Australia since 1999. Its annual reports represent some of the most reliable population-level outcome data available anywhere in the world.

Total knee replacement: what the registry shows

The AOANJRR measures longevity by tracking the cumulative revision rate — the proportion of knee replacements that have required a further operation at various time points. For primary total knee replacement, the data is reassuring:

At 10 years, approximately 95% of total knee replacements are still in place. Around 5% have been revised.

At 15 years, approximately 91% remain in place.

At 20 years, approximately 85–87% of total knee replacements have not required revision.

These figures represent outcomes across a very large number of patients over many years. They are not predictions for any individual — they are population averages. Some patients will do better; a small number will not do as well. But as population-level data goes, this is an excellent result.

For the majority of patients over 65 having a knee replacement today, there is a high probability the implant will last the rest of their life. That is a meaningful statement to be able to make with confidence.

Partial knee replacement: a different picture

Partial (unicompartmental) knee replacement — which replaces only the damaged compartment of the knee rather than the whole joint — has historically had a higher revision rate than total knee replacement. The AOANJRR data consistently shows cumulative revision rates of approximately 9–10% at 10 years for unicompartmental replacement, compared to around 5% for total knee replacement.

This does not mean partial knee replacement is a worse procedure — it means it is a different procedure, used in a different patient population, with a different failure mode profile. The higher revision rate partly reflects the fact that patients with partial replacement are often younger and more active, and partly reflects that some revisions are to total knee replacement as a planned progression rather than a failure of the partial implant itself.

When partial knee replacement is well indicated and carefully executed, the medium-term outcomes are very good, and recovery is typically faster than total knee replacement. The AOANJRR data helps surgeons and patients make an informed choice between the two options based on real-world performance.

Why some replacements are revised earlier than others

The most common reasons a knee replacement requires revision include aseptic loosening (the implant gradually loosening from the bone without infection), polyethylene wear (wear of the plastic bearing surface), instability, stiffness, and infection. Each of these has a slightly different time profile: loosening and wear tend to be long-term issues, while infection and instability are more likely in the early post-operative period.

Infection is the most serious cause of revision and, while uncommon, carries the most significant burden for the patient. Strict surgical protocols and careful patient selection — including management of conditions like diabetes and optimising nutritional status before surgery — reduce the risk.

The age effect in knee replacement

As with hip replacement, age at the time of surgery is the single strongest predictor of whether revision will be needed. Younger patients are more active (placing more mechanical demand on the implant), and they have more years ahead of them in which revision might become necessary simply due to time.

The AOANJRR data reflects this clearly. Patients under 55 having total knee replacement have significantly higher 10-year revision rates than patients over 75, not because the surgery performs differently but because the time horizon is so much longer. This is an important part of the conversation when younger patients are considering replacement surgery — not to discourage them, but to set appropriate expectations and discuss timing carefully.

What implant choice and surgical technique contribute

Implant design matters. The registry tracks performance by brand and design, and there are meaningful differences between implant systems in their long-term revision rates. Choosing an implant with a strong registry track record is one of the decisions a surgeon makes on behalf of the patient.

Surgical technique also plays a significant role. Accurate implant positioning — ensuring the correct alignment, rotation, and balance of the knee — reduces the risk of premature wear, instability, and stiffness. Robotic-assisted surgery, such as the MAKO system, achieves more consistent implant positioning than conventional manual technique, and emerging registry data supports lower short-term revision rates with robotic-assisted cases.

What all this means for you

If you are considering a knee replacement, the AOANJRR data offers real reassurance. Total knee replacement has an excellent track record over 20+ years of registry monitoring. The majority of patients who have the operation will not require revision, and those who do are typically operating in a context where revision surgery remains a viable and well-established option.

The right approach is to discuss your specific circumstances — your age, activity level, bone quality, the degree and distribution of arthritis, and your goals — and make a decision based on the best available evidence. That is a conversation worth having in detail at your consultation.