I was born with a bone deformity that gave me hyper flexibility of the ankle and foot, but severe bowed out flat feet. By 10 y/o I couldn't run, jump, stand on tip toe, walk fast, walk for a long time or stand too long.
Finally got major surgery at 20 and 21 for it. IT WAS TOO LATE and the reconstruction made it so much worse that I know have a handicap decal.
My daughter was born with the same deformity and thank goodness I could see the signs. Her pediatric ortho completely wrote off my concerns so I went to the specialist who did my feet. He immediately saw what I did and we waited a year to do her surgery. Just a few months after her 4th birthday she had metal implants in both ankles and is doing great!
Take him to a specialist to talk about possible corrective surgery and do it BEFORE his growth spurt. After the growth spurt means his muscles, ligaments and tendons will conform to the disability and cause more pain.