What does the AOANJRR say about total knee replacement?

Total knee replacement is one of the most commonly performed elective surgical procedures in Australia. Tens of thousands of operations are carried out each year, and that number has grown steadily as the population ages. With such volume comes an enormous amount of data — and much of the most useful data comes from the Australian Orthopaedic Association National Joint Replacement Registry, the AOANJRR.

What is the AOANJRR?

The AOANJRR is a national database that has been tracking joint replacement surgery in Australia since 1999. Every hip and knee replacement performed across the country is reported to the registry, along with information about the patient, the implant used, and whether the implant required revision at any point. Because capture rates are very high — approaching complete coverage of procedures performed in Australia — the registry gives an unusually reliable picture of real-world outcomes at scale.

It is not a marketing tool. It is a clinical accountability mechanism, and it is one of the reasons that outcomes in Australia compare very well internationally.

How common is total knee replacement in Australia?

Total knee replacement is among the most frequently performed elective operations in the country. Demand has risen significantly over recent decades as the population ages and expectations around mobility and quality of life have increased. The AOANJRR captures each of these procedures, making the Australian dataset one of the largest and most comprehensive in the world.

What do the revision rate figures show?

The most commonly quoted measure of implant performance is the revision rate — how often a knee replacement needs to be reoperated on. The AOANJRR data shows that for primary total knee replacement, the cumulative revision rate is approximately 5 per cent at ten years, roughly 9 per cent at fifteen years, and in the range of 14 to 15 per cent at twenty years.

These figures represent population-level averages across all implant types, all surgical approaches, and all patient profiles. Individual outcomes vary meaningfully depending on factors including age, activity level, body weight, implant selection, and surgical technique.

What does "revision" actually mean?

It is worth being clear about what a revision rate represents. A revision is any reoperation that involves removing or replacing one or more components of the original implant. Not all revisions indicate catastrophic failure. Some involve replacing a worn polyethylene liner — a relatively minor procedure. Others are for infection, instability, or mechanical loosening, which are more significant operations.

Conversely, patients who have pain or dissatisfaction but do not undergo reoperation are not captured by the revision rate. This means the revision rate is a useful but incomplete measure of how well a knee replacement is working for a patient.

Why do some implants perform better than others?

One of the most valuable outputs of the AOANJRR is the ability to compare implant brands and designs directly. The registry reveals meaningful differences in revision rates between different implants, and some designs perform substantially better than others over time. This information directly informs implant selection in clinical practice — surgeons who use the registry data tend to gravitate towards implants with strong long-term track records and move away from those showing early warning signals.

This is one of the registry's most important functions: it creates a feedback loop between outcomes and practice that benefits future patients.

What does the registry show about robotic assistance?

Robotic-assisted knee replacement is a relatively recent development, and the AOANJRR is beginning to accumulate enough data to draw early conclusions. The emerging picture is encouraging: robotic-assisted procedures show lower early revision rates compared to conventional technique in some analyses, likely reflecting more consistent implant positioning. Longer follow-up data will be needed to confirm whether this advantage is sustained over ten years and beyond, but the early signal is a positive one.

Does age and sex affect outcomes?

Yes, and the registry data makes this clear. Women and younger patients both show higher revision rates than older patients, across all implant types. For younger patients, this reflects the simple arithmetic of longer follow-up — a 55-year-old undergoing knee replacement has more years ahead of them during which a revision could occur than a 75-year-old. For women, the reasons are more complex and are an active area of research.

This does not mean younger patients should not have knee replacement. It means the conversation about timing, implant choice, and expectations should be more detailed and more tailored for this group.

What about patient satisfaction?

Revision rates capture what goes wrong. Patient satisfaction data captures something different — how people feel about their knee. Large studies consistently show that the majority of patients — roughly 85 to 90 per cent — are satisfied or very satisfied with their total knee replacement. That is a strong outcome for a major surgical procedure.

However, a meaningful minority of patients — roughly 10 to 15 per cent — report dissatisfaction, even in the absence of a technically identifiable problem. Unexplained pain, a sense that the knee does not feel natural, and unmet expectations are the most common themes. Understanding this before surgery — having a realistic conversation about what the operation can and cannot deliver — is one of the most important parts of the pre-operative consultation.

Registry data gives us a population-level picture. What matters in the consulting room is how those numbers apply to you, specifically.

What does this mean in practice?

For most patients considering total knee replacement, the registry data is reassuring. A well-performed TKR using a proven implant has an approximately 95 per cent chance of still being in place at ten years — a strong track record for an operation that has the potential to dramatically improve quality of life.

The registry data also reinforces the importance of implant selection and surgical quality. Not all knee replacements are the same, and not all implants perform equally. Choosing a surgeon who uses registry data to inform their practice — and who uses implants with a proven long-term track record — is one of the most important decisions a patient can make.