You only get knee and back problems when you're old, which is because the body just stops repairing itself as effectively as it does when you're young.
It's going to be far easier to re-enable the ability to self-repair our bodies as we do in youth than to completely change the function of two of our limbs.
Completely false. Lots of people in their 20s have knee and back problems. Torn ACLs are common in athletes and people who participate in sports. I had a coworker a few years ago who had his ACL replaced; he was in his mid-to-late 20s.
Please re-read and reconsider the context of my post. This reddit-tier "must seek to contradict and attack others" behavior doesn't do anyone any good.
It's going to be far easier to re-enable the ability to self-repair our bodies as we do in youth than to completely change the function of two of our limbs.