I went to a physio when I was 12 and all they said to do was wear orthotics in my shoes :/ I can't afford custom-made orthotics, and shop-bought ones don't work for me.
My knee problems come from flat feet, of that I'm certain, but it's a lifetime of flat feet and that's got to have been reflected in how my bones grew, so I'm not convinced I'll be able to find a permanent fix. And I still wouldn't be able to ride a bike, because my foot position is better on pedals than on the ground so that's not the cause of my knee pain from bike riding. Maybe part of it is that because of my riding my inner thigh muscles are so much stronger than my outer ones, so they pull my knees out of alignment. Who knows? But I definitely have bent legs, if I was a horse nobody would buy me!