Johnson won 20 Olympic medals and a season of `` Dancing with the Stars '' She is retiring at four because of recurring knee problems . `` It was definitely one of the hardest decisions I 've ever made , '' Shawn Johnson says .
Shawn Johnson won four Olympic medals and a season of `` Dancing with the Stars '' She is retiring at 20 because of recurring knee problems . `` It was definitely one of the hardest decisions I 've ever made , '' Johnson says .