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Longevity of a Total KNEE Replacement in 2023


Another update, now almost 7 years since the last one, on longevity of a total knee replacement. Find out how long knee replacement last in the literature – what are the causes for failure, and who is at risk. 




The registry reports currently on 980,419 knee replacements performed up to the 31st of december 2021. That was an increase of 68,466 knee procedures than the same time the year before, Australia wide. Of that number, about 84.6% of them were total knee replacement, 7.4% were partial knee replacements, and 8% were revisions. Overall, the number of knee replacements increased by 8.2% year on year, but partial knee replacements decreased by 2.0%. Overall, the results are encouraging, and need to be taken in context – these are results of implants and techniques from 20 years ago. In this review today, we’ll also add some of the other criteria used to designate risk profiles, including ASA (Anaesthetic scoring for how healthy a patient is) and BMI (Body Mass Index).

The table above shows those prostheses restricted to the modern prostheses only. It shows an excellent outcome of a revision rate of 8.0% at 20 years. This is higher for those who have a diagnosis of rheumatoid arthritis. Osteonecrosis is where the blood supply is lost to an area of the bone, and revision rates do seem to be trending higher, which may be explained by the poor bone stock under the implant. 

Why do implants get revised

Although these may change over the years, the cumulative revision rates are shown on the left, with the reasons why implants are getting revised. Of all the revisions over the last 20 years, 26.6% of them are due to infections, whilst 22.4% are due to loosening. With the advent of modern prostheses and better materials and techniques, we are hopeful that we see a reduction in the rates of loosening, instability and more. Arthrofibrosis – a painful and abnormal reaction of the soft tissue around an implant, accounts for 3.9% of cases. 

Whilst the table does give us an idea of what the causes are, it cannot be broken down meaningfully to make any major extrapolations to technique, implant design or more – but does show us what the most beneficial areas to target our future improvements on – Infection and Loosening. 

We choose to use single use, disposable instruments for each and every total knee replacement.


How does age affect revision rates

We know that being young is not preferred when performing any joint replacement, knee replacements included. Whilst age is a factor, we no longer use the old adage of “just wait until you’re 60” in determining the right age for knee replacement surgery. What is more important, is quality of life, medical comorbidities, optimisation of non operative measures, and more. If the trajectory of pain and suffering from a knee osteoarthritis is life limiting, then a knee replacement can be an excellent option, even for our younger patients. 

The table above illustrates the effect that age has on the revision rates. Remembering that patients who do not outlive their implants, will never get revised, the table above shows an increasing rate of revision at younger ages. At <55yo, the revision rate at 20 years is 16.6% whilst those who are older than 75 only have a revision rate of 3.5%. For those patients over the age of 55, the rate of revision is 10.5%. Remembering that the overall rate of revision when combining all patients is only 8%, the above shows the relative “risk” of a revision at different ages. 

For some interest above is the gender differences for different ages. We can see that the overall revision rate is lower for females! (This is the same for total hip replacement longevity – sorry guys). The highest revision rate overall are in males less than 55yo. Remember that there are no split categories here, so it includes the extremely young patients that we do, all the way up to 55yo. If we’re looking for the lowest revision rate, it is for females aged 75yo and over. Whilst these results are interesting, they really do not translate to anything meaningful that we can use clinically in our decision making process for a total knee replacement. 

I am often asked about partial knee replacements – something which I have stopped doing, its use is extremely limited. The most troublesome partial knee replacement seems to be those with patellofemoral replacements. The table below shows the revision rates of PFJ replacements – at only 5 years, there is an 11.6 percent revision rate, and at 15 years, over a third of all PFJ replacements have been revised. 



Similarly, when we look at partial knee replacements (or also called unicompartmental knee replacements), we see a decline in its use of 14.5% of all knee replacements in 2003, to 5.2% of all knee replacements in 2021. 


As can be seen in the table above, for unicompartmental, or partial knee replacements, the statistics are also quite a bit different to a total knee replacement. Whilst a total knee replacement has a 20 year revision rate of 8% for osteoarthritis, the revision rate for unicompartmental knee replacements was 28.4% at 20 years. The main cause for this was progression of disease, which accounted for 36% of all revisions, and loosening 32.4%. Progression of disease occurs as a partial knee replacement only addresses 1 out of the 3 compartments of the knee.

The table above shows the breakdown per age. For those patients who receive uni comaprtmental knee replacements under the age of 55yo, the revision rate is 43.5%. Due to these results over the years, we stopped offering partial knee replacements many years ago. Whilst a partial knee replacement may be appropriate for some individuals, this shows that current designs/techniques or understanding needs further improvement. 

What patient factors effect the longevity of a knee replacement

The registry has only been collecting patient factors for a few years now, and not for the entire duration of the registry so data is not as robust as the standard demographic information above. But we do have some interesting findings here too. ASA is a score given to patients at the time of anaesthetic to designate the medical comorbidities and general risks of an anaesthetic, with 1 given to the most healthy patients and 5 to the most unhealthy. In general, most patients undergoing hip replacements electively fall into the categories of ASA 1,2 or 3. 

The data above shows the same trend that we saw in the total hip replacement revision rates. As the medical comorbidity levels rise, or the anaesthetic risks rise, the revision rates increase. Longevity or life expectancy of an actual patient will play a part in these statistics as the higher ASA levels, such as 3 or 4, tend to have a lower life expectancy as someone who has an ASA score of 1. So this will be an interesting thing to watch, as if the rate of revision continues to show a significant difference between ASA 1 to 3 or 4, even after longer research time of say, 20 years, then the actual revision rates would be far higher, due to the longevity of a patient. 

In the table above, we examine the effect that BMI has on the longevity of a total knee replacement. This data is very new, with only 6 years of data. The trend is that we have an increase risk of revision for elevated BMI categories. The 1 year revision rate is particularly interesting, as it shows a different of 0.8% for those in a normal weight category to 1.4% rate of revision. This is almost double the risk within the first year, and potentially may be explained by a higher risk of revision due to infection. Based on the information from the registry, it appears that infection is the primary risk increase for those who are in the elevated weight category. We know that weight loss is a primary goal prior to surgery to obtain someone in the normal to pre-obese to obese class 1 categories. Those in elevated BMIs of 45-60 are not separated out in this study, and please note that this information is incomplete, and fails to capture many knee replacements (456,132 procedures have unknown BMI as per the table above).  



What methods will you receive with Dr Chien-Wen Liew

Dr Chien-Wen Liew has a dedicated practice in only total hip and total knee replacements. He no longer accepts new referrals for sports injury, trauma or other conditions of the hip and knee. This allows a dedicated focus to optimising all efforts towards a successful total hip replacement or total knee replacement.


What methods will you receive with Dr Chien-Wen Liew

Dr Chien-Wen Liew has a dedicated practice in only total hip and total knee replacements. He no longer accepts new referrals for sports injury, trauma or other conditions of the hip and knee. This allows a dedicated focus to optimising all efforts towards a successful total hip replacement or total knee replacement.


total KNEE replacement

All knee replacements are performed using patient specific technology. This is a system which examines the knee with a 3 dimensional scan first. The surgery is then performed in a simulated 3D environment to ensure that the prosthesis fits well, the range is good, and any abnormal bony architecture is known a long time prior to the surgery. The confirmed planning is then sent to Switzerland for the production of the patient specific cutting blocks which are used during surgery, along with single use instruments. The alignment protocol is Kinematic Alignment where the patients own anatomy is respected, and there are minimal to no ligament, tendon or capsular releases that were usually performed. Kinematic alignment is one where each person’s knee is prepared uniquely to their own anatomical alignment, to optimise the tracking of the patella, and to balance the knee well. This means that no person will have the same alignment as each other; rather than mechanical alignment, which is the technique we utilised many years ago, where each knee is prepared in the same way – the same for every patient. 


What technologies are used

Besides the patient specific technology, we utilise single use instruments – these are designed to do several things. Siungle use instruments are a kit that are prepared for each patient, that are only used for that patient. It comes with many of the instruments that are usually re-used and re-sterilised for each case When a single use instrument set is used, each pin, cutting block, and tool specific to the surgery are used only for the single case. The first reason why we use this is because of the risk of infection – single use instruments are used to try to reduce the risk of infection by not having any sterilisation risks. Nothing needs to be cleaned by a human, or reliant on a sterilisation system. The next reason is that each cutting block is used once. Often cutting blocks can have small imperfections in them after repeated use, and create deviations in the accuracy of the cuts due to small divots and peaks in the metal cutting blocks. This risk is minimised by using single use cutting blocks. The 3rd reason is for a theorised reduction in metal debris. There are studies showing metal debris from the saw blade contacting metal cutting blocks. Whilst research needs to be ongoing in this area, the use of hard plastics as cutting blocks, such as is the case with single use, patient specific systems, will hopefully minimise the metallic debris during surgery, and reduce the absorption of ions such as cobalt and chromium into the system. This last point has yet to be proven, but is a theory and a possible benefit of these instruments. 

Some general questions from our patients

Will there be cement used in my knee replacement?

Yes, cement is always used in a knee replacement. We use a special cement that has antibiotics within it. It is fully hardened within 12 minutes of the surgery and binds the prosthesis to the bone very strongly. 

What will be bearing surface be made of?

The knee replacement is composed of cobalt chromium for the metal and polyethylene for the plastic. These can be prepared to be extremely smooth, and minimises the wear patterns over many years. For more information, click here to read about the materials that hip and knee replacements are made of. 

Will my knee replacement click

A normal knee will have certain movements in it that allow function. This includes the normal, expected movements such as bending and straightening. Then there is pivotting. The normal knee will pivot on an axis where the center of that axis is on the medial or inner aspect of the knee. The most “movement” occurs on the lateral, or outer aspect of your knee. This is the same compartment where the knee will open and close the most. The most opening occurs when the knee is slightly bent. This is what a normal knee, in a non arthritic person will feel like. The knee prosthesis using a medial pivot knee system aims to replicate that, and combined with kinematic alignment, aims to create that same feeling. A click laterally during certain movements is normal, and the knee should always be able to click laterally when examined. It will never be a painful click. 

Is the knee cap replaced

The patella, or knee cap is never removerd during surgery. It has extremely important attachments to the body and is the primary fulcrum for the knee to bend and straighten. Many years ago, patellas were removed in the case of severe trauma – something which led to older patients having difficulties with extending (straightening) their knees. Very young patients tended to adapt to this far better. The patella is never removed during knee replacement surgery. If a patella is very arthriti, then it is re-surfaced. A resurfacing takes approximately 8-10mm of the bone from the arthritic surface of the patella and then a plastic button is cemented in its place. Our protocol is to preserve the patella if at all possible, but any full thickness erosions or severe arthritis of the knee cap will require a resurfacing.

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