August 24, 2021

Pain improvement after a total knee replacement - will both my knees respond the same?

Written by Mrs Margy Lewis

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It is generally accepted that the total knee replacement of the other knee does not give the same pain relief as that of the first. It also seems that it does not actually matter whether the knees are done during the same session (I used to do bilateral knee replacements in younger, still working patients but not any more as the risks outweigh the benefit) or if the second knee is replaced later. The first one will almost always outperform the second one on PROMs (Patient Reported Outcome measures).

I first noticed this a while ago but there was no good explanation. I tried to think what else in my life exists in a two: children! Although they really should be copies of one another, they never are. Having said that, I soon realised that this explanation does not directly correlate to total knee replacement patients for I cannot say that the first child always outperforms the second. With the example of the first and second child, this rule is not set in stone but when it comes to knee replacements, it is most probable that the first knee replacement will be better than the second - at least in the majority of patients. The one exemption are patients who were unhappy with the outcome of their first knee replacement. In this subgroup of patients, the odds are that they will be more satisfied with their second knee replacement - the second knee replacement will outperform the first one.

This forced me to think about it. It is a simple fact that if the patient is experiencing pain and symptoms from both knees, they will always ask to have the more painful knee replaced first. Interestingly, the radiological (x-ray) signs do not correlate positively with the amount of ‘trouble’ the knee is causing. This means that it is more likely that the knee, which shows less severe degenerative changes on an x-ray, is causing more pain and discomfort. From there, the conclusion is quite simple: the knee, which is causing more pain, is replaced first and thus the relief and benefit felt by the patient is greater in comparison to the other knee, which is causing fewer problems.  

This can be explained using the VAS score (a score system with values from 0 to 10, where 0 means no pain at all and 10 is the worst pain possible). For example if the VAS score at the time of having the first total knee replacement done was 8 (this is very likely combined pain from both knees) and then it was reduced to 2 (the other knee is still hurting), the improvement was 6 points (I call this relative improvement). When the other knee is done the preoperative VAS score is very likely less than 8 (let me use 7), and when the total knee replacement is done the VAS score is again 2, the relative improvement is 5 points only. In the second total knee replacement the improvement was less (1 relative point less) but unfortunately patients do feel it as a significant difference.

In conclusion, there is no doubt that a total knee replacement is a very effective procedure mainly for pain relief. It is not as effective in improving function but we do need to accept the knees will behave differently even with the same procedure.

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