Okay, now that I've seen some of him just standing... he seems to have longish, sloping pasterns that might appear more dramatic (when flexed) than other horses with shorter or upright pasterns. I had this problem with my horse and a scare with an ignorant vet (Dropped fetlocks (this is long!)
) when in reality, he was just fine (it was a separate and much less dramatic issue causing him to weight his back legs differently). I received some very useful responses to that thread about healthy fetlock flexion.
What is of some concern is how different his front pasterns look as compared to his back. Do they appear different in length and slope in real life, or just in these pictures?
Again, I wouldn't panic just yet. :) See what a vet or your farrier says. By the way, your boy is very handsome!
For now I would ask your farrier to give him short a short toe/breakover, to support that joint.