You hear a lot of things said about knee replacements, often quoted by an interesting variety of ‘experts’! However, one of the very common dilemmas faced by many patients is when might actually be the right time to go ahead with knee replacement surgery.

Knee replacement surgery is a major op, and not something to be entered into lightly. The operation takes about 1½ hours and is pretty painful early on post-operatively (but that’s what painkillers are for). It can take up to 6 months for people to fully plateau in their recovery from a knee replacement, and an artificial knee is never as good as an original natural knee. The patient satisfaction rates after knee replacement are about 85% with a standard knee prosthesis, and up to about 95% if a custom-made Conformis prosthesis is used – but either way this is not a 100% ‘guaranteed’ operation. The surgery also carries with it small potential risks, such as infection, nerve/blood vessel damage or blood clots.

So, you should only consider having knee replacement surgery if your symptoms and/or functional restrictions actually feel bad enough to justify the pain, the hassle, the time required for the rehab and the potential associated risks of surgery.

Some people say that you should only ever have a knee replacement as a very last resort, and that the surgery should be delayed for as long as possible. This is not actually correct.

It’s certainly true that it’s preferable not to have knee replacement surgery too young. This is because the younger you are when you have an artificial joint, the more you’re likely to use it … hence, the more movement cycles there are through the joint and the greater the forces and any impact will be — and therefore there will be a faster rate of wear and tear in the joint. Knee replacement prostheses consist of a metal surface on the end of the femur, a metal surface on the top of the tibia and a very hard plastic washer in between. These artificial materials do not repair or regenerate themselves with time, and hence any wear is cumulative, and eventually knee replacements can wear out. So, the younger you are when you have a knee replacement and the more you use it, the faster the rate of wear and tear will be and the quicker it will wear out. On top of this, the younger you are, the longer you’re likely to live – and hence the longer you actually need the knee replacement to last.

If a knee replacement is done in a patient in their 70’s, then there is only a risk of about 10% of the prosthesis failing within the patient’s lifetime. If a knee replacement is done in a patient in their 50’s, then there is an approximately 50% chance of it wearing out and failing within the patient’s lifetime.

If a knee replacement fails, then it can normally be removed and replaced with a new one, which is called a revision knee replacement. However, revision knee replacement surgery is twice as complex and difficult as the first one (the primary), with double the potential complication rates and with lower patient satisfaction rates and functional scores. Also, revision knees then tend not last as long as a primary knee. It’s not normally technically possible to just continue revising and revising a knee replacement, and if things get too bad then sometimes it’s necessary to simply fuse the knee (an arthrodesis).

So, the best way to avoid the potential downward spiral of revision surgery and failing knees is not to have a knee replacement too young … but this means ‘not unnecessarily young’. We do sometimes do knee replacement surgery on patients as young as in their 40s – but only ever as a last resort. 50’s is ‘OK’-ish. 60s is perfectly acceptable.

On top of all this, however, it’s important to consider the other side of the timing equation… which is that equally, you shouldn’t actually leave a knee replacement too long!

If you do a knee replacement in a younger patient who’s medically fit and who’s got strong, fit, flexible muscles, and in whom the joint damage is not so severe, then the patient is less likely to suffer complications, they’re more likely to cope better with their rehab and they’re more likely to achieve a better final outcome from the surgery. Conversely, the older a patient is, the more medical problems they have, the less fit they are, the weaker they are, the stiffer the knee, the more deformed the joint and the more bone loss/erosion there is, the poorer the outcome from knee replacement surgery is likely to be.

If you’re able to cope with your knee symptoms, if you’re able to tolerate the pain or manage it through painkillers, anti-inflammatories and/or supplements, and if you’re still able to manage your activities of daily living and you’re still mobile enough to manage some gentle exercise and maintain your fitness levels, then you should not go ahead with knee replacement surgery.

For most people, their symptoms will just gradually get worse with time. When the symptoms cross a certain threshold, which is different for every individual, the knee will then become a significant rate limiting factor and will prevent the patient from being able to exercise and function properly. From this point onwards there’s likely to simply be a continuing downwards slope, with a gradual decrease in function. If/when you hit this point and your symptoms cross that threshold and your function starts deteriorating on that inexorable downward slope…. that’s the time to have your knee replacement surgery.

Ultimately, everyone’s different and everyone’s got their own tolerance levels, their own fears and their own aspirations, and if / when to potentially have knee replacement surgery is a very personal and individual decision. The job of your surgeon is to explain to you what’s actually going on with your knee (the diagnosis) and to explain all the different potential appropriate treatment options, along with their various pros and cons, and to advise you and assist you in gaining an understanding of your condition and coming to the right decision for you about what you might want or need to have done… and if you’re still not clear or not sure, then it’s your job to ask your surgeon for more information or for a further proper face-to-face discussion with them back in clinic.