Although his weight and overall health is improving dramatically, the number of scars on his hind legs speak to a past of use as a "tripping horse." In accordance with that, his left hind stifle appears to have suffered some major injury, likely acquired while put through the torturous practice.
When we return to the vet hospital for his gelding, diagnosing Chiron's lameness will come first. Since up until now, he's been too weak to do more than just walk, patience is key. But clearly, he feels well enough to at least try to be the horse he once was.