There are around 60 thousand knee replacements performed every year in Australia. This number is growing on an annual basis. One of the most common questions asked of an orthopaedic knee surgeon, is that of how long does a knee replacement last? While it is not possible to give an exact answer for any one individual, we are certainly able to look at the bigger picture to help advise our patients. The Australian Joint Registry assesses the ‘survivorship’ of knee replacements. Essentially this refers to how long a knee replacement lasts prior to an exchange of one of the components (Revision knee replacement). For the purpose of this article, we will focus on total knee replacements. Dr. Smith takes a look at some of the important variables and how these influence the survivorship of a knee replacement.
What is the underlying Diagnosis
While a knee replacement is generally reserved for patients with underlying ‘arthritis’, it is possible to divide this umbrella term into further categories. Degenerative osteoarthritis is the most common cause of ‘arthritis’ in the community. This is often referred to as ‘wear and tear’ arthritis. For this condition, there is a 93% survivorship of the knee replacement after 15 years. This indicates that 93% of people that have a knee replacement performed for osteoarthritis, will not require a ‘revision’ procedure during the first 15 years.
Interestingly, patients with rheumatoid arthritis, an inflammatory condition, have a slightly improved ‘survivorship’ in comparison to osteoarthritis. A small portion of patients undergo a knee replacement for osteonecrosis, which is a condition where the blood supply to the subchondral bone is impaired. This subset of patients have a slightly higher risk of requiring further procedures in the future.
Total Knee Replacement – Implant Characteristics
There are many different knee replacement designs and prostheses available to an orthopaedic surgeon. The Australia Joint registry is a powerful tool that enables surgeons to analyse the ‘success rates’ of these different implants, across thousands of patients. While the majority of these implants fall within a similar ‘survivorship’ rate, it is important that a Surgeon is aware of the results of the implant that they are using. Implants that are found to have an unacceptably high ‘revision’ rate are notified by the registry, and are typically removed from the market.
Different methods of ‘fixation’ of the implant (cemented vs uncemented vs hybrid), design of the articulation, and whether the patella (knee cap) is resurfaced at the time of the procedure, all play a role in determining the ‘average’ survivorship of the implant.
How long does a knee replacement last ? – Why Age is important
The age of the patient undergoing the knee replacement is one of the major factors contributing to the survivorship of the implant. It makes sense that a younger more active patient will ‘wear out’ their knee replacement at a faster rate than an older more sedentary one. This does not mean that young patients should not undergo a knee replacement. If younger patients have debilitating arthritis, and are not suitable for an alternative procedure such as a knee osteotomy, a knee replacement may be required to improve quality of life.
Looking at age as an individual factor, people under the age of 55 at the time of their knee replacement, have a 85% survivorship at 15 years. This is in comparison to 97% survivorship in people over the age of 75 at the time of the procedure.
Gender – Is it important?
Like most things in life, knee replacements in males have a slightly lower (1% difference at 15 years) ‘survivorship’ in comparison to their female counterparts. This is thought to be due to a small increase risk of infection in males, although the total number of these are still very small.
Does Computer Navigation make a difference?
Computer navigation refers to a specialised technique that is utilised at the time of surgery during positioning of the implants. A computer based program inputs data during the procedure, and acts as a guide for the surgeon during the positioning of the implants. Recently the joint registry has shown that in patients under the age of 65, knee replacements performed with the use of computer navigation have a small improvement in survivorship compared to traditional instrumentation.
What does this all mean?
As you can see, there is no ‘black and white’ answer to the question ‘How long will my knee replacement last?’. If you would like to make an appointment to discuss this further with Dr. Smith then please contact his rooms to make an appointment. Other treatment options may also be available.