Fuck, I never knew that about knees. It's amazing how good you have to be to get things right, or at least wrong in a way that people don't pick it to death.
I still don't get it. Looks fine to me. Can't you rotate your feet side to side around ankle without moving your knees? The only part that's strange is the blocky shadows under the knees but you could just interpret that as the style of shading.