I agree with Elana almost verbatim. I see the bench knee, but only in his left knee. But it's there. I also saw the back at the knee. But on the good side, he has lots of bone in his hock and shoulder and fetlocks, very clean hocks (no swelling at all). He looks overall really sturdy and I would think he could do anytihing but might not be so good for hard core jumping.
Have you tried adding some oil to his feed? (for his feet)
He looks a bit like he could pack on the weight pretty easily. Ride him, lots!