The tendons narrow at the knee and it is a conformation flaw plus a serious weakness (IMO).
When looking at babies, this saying comes to mind: "Tops may come but bottoms never!" This means that what you see is what you get with a young horse's legs while the body structure will change quite a lot. I believe in this saying having watched a large number of baby horses grow up. .
There is something about the outside of a horse that is good for the inside of a man. ~Winston Churchill
) Dinosaur Horse Trainer