How long a Total Knee Replacement Lasts
A Total Knee Replacement is a highly successful operation, with most patients being extremely happy with their result. The worldwide literature however, suggests that only 80% of patients are truly good or excellent when questioned about their knee. In a proportion of people, a knee replacement does not last long, and our research shows us that this can be due to a variety of reasons. There are many types of knee replacements. The main types include:
- Unicompartmental knee replacements (Where only 1 compartment is replaced)
- Total knee replacements (Where the entire knee is replaced). This may or may not include the patella.
- Patellofemoral Joint resurfacing
These types of knee replacements have variable survival rates, due to many reasons which can be related to the patient, the surgeon, or the type of implant and way it is inserted.
Total Knee Replacements
A total knee replacement is performed when there is osteoarthritis in the knee. As of the 31 Dec 2014, over 400,000 total knee replacements were studied in the Australian Registry. This registry captures almost all total knee replacements inserted in Australia and is one of the most respected registry’s in the world, as it is mostly compulsory.
Total knee replacements are increasing in their use, and there were 5.2% more total knee replacements in 2014, than 2013. The 2015 results are becoming available soon.
Osteoarthritis accounts for 97.5% off all reasons for a total knee replacement (TKR) with females more likely than males to receive one (56.1%). Younger patients still account for a much smaller proportion of cases, with only 6.7% of TKR’s being performed in patients under 55 years old.
The most common reasons for a revision (2nd surgery) is loosening of the prosthesis. Infection was the 2nd most common.
For all cases of total knee replacement, at 14 years, 7.2% of total knee replacements required revision, meaning that 92.8% of total knee replacements were still surviving from their original insertion. The table below shows this in more detail.
Age is a major factor when it comes to revision. The younger you are, the higher the potential there is for revision. As can be seen in the next chart, if you had your total knee replacement when you were less than 55 years old, your revision rate is 14.9% at 14 years compared to over 75 year olds, who have a revision rate of 3.3%.
The reasons for why younger patients need more revisions is still being studied, but most likely relates to higher demand, more weight being put through the prosthesis, and may improve with newer techniques and technology.
Partial or Unicompartmental Knee Replacements
A unicompartmental knee replacement is one performed when the arthritis is isolated only to one side of the knee. This can be on the inner (medial) or outer (lateral) sides of the knee. This requires a knee that has good ligaments, and no major deformities. The use of unicompartmental knee replacements is becoming less popular over time. Its usage has dropped by 45.8% since 2003. 99% of cases are performed for osteoarthritis. Unicompartmental knee replacements are an excellent option when there is no arthritis in other compartments of the knee, and have been shown to have excellent characteristics when a revision is required, as there is minimal damage done to the knee at the time of the initial surgery. However, the number of patients where this is suitable is not large, which may account for the decrease in its use.
The revision rate for a unicompartmental knee replacement at 14 years is 20.5%, meaning that it is 3 times the revision rate as a standard total knee replacement. The following chart shows the revision rate at various time points.
Patellofemoral knee resurfacing
These are the least common knee replacements performed. This involves resurfacing the groove that the knee cap (patella) sits in, as well as the patella surface itself. It is mostly performed in females (76.8%) due to the fact that the groove (trochlear) is deficient most commonly in females. Multiple patella dislocations can be a risk factor for damaging the cartilage in the patellofemoral joint. In a total knee replacement, the trochlear is automatically replaced, and occasionally the patella is resurfaced at the same time.
The rate of revision of patellofemoral resurfacing is the highest of all the types of knee replacements. At 10 years, 27% are revised. There is no Australian data past 10 years at present. The following chart shows this. In comparison, the revision rate of a total knee replacement at 10 years is 5.5%; unicompartmental knee replacement at 10 years is 15%. The table below shows the revision rate of patellofemoral joint replacement over 10 years.
Overall, total knee replacements are excellent procedures. They have the best revision rates of all kinds of knee replacements, however in some cases, partial knee replacements are required when a patient has very isolated arthritis. This data cannot tell us why implants are being revised, but gives us an understanding of trends, and allows surgeons to strive to provide the best options for their patients at all times.
For further information, please contact the rooms of Dr Chien-Wen Liew on (08) 7099 0188
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