You just need to get home earlier plym. Oh, and lay off the ale for a while.
Trouble with knee Ops Joe is they only last a while and you can't keep having them. If you have it done too young then it is likely you will still end up with a bolloxed knee after a while. My brother-in-Law had his done after years and years of waiting. The waiting was because of his age and being told they only last around 10 to 15 years. In the end they did it because he was getting to the point of not being able to walk at all. They replaced the knee, then operated again to "tidy up the bone fragments", then operated again to "tidy up the bone fragments". Then after another Op they finally managed to sort him out.............mostly. I think it's because the knee joint is hardly rested and wears too easily once there is a problem.