A lot of people watching the show misunderstand the simplifications the animators do to pony bones. Despite its simplifications, the horses use real life equine anatomy, and it’s really obvious when they’re doing things.

The raised bump at the back of the leg is called the hock. It isn’t where the joint is, but actually the location of a bone over the location of the joint. That’s when when ponies move around in the show, that bump stays there, always.

The show does shorten the length of the gaskins–the leg segment under the thigh–but it still doesn’t go parallel to the ground, like lots of people try to draw it.

An animal with a leg section that’s parallel to the ground wouldn’t be able to support its own weight. Every animal in nature has smooth angles in their leg bones. Even birds, who have pretty sharp diagonals, have very reasonably balanced legs.