Horses are incredibly tough animals, brave, hardy and durable. At the same time, in the wrong combination of circumstances, they may as well be made of glass.
Sadly, horses have no way back from the wrong kind of leg break , here is why according to the Guardian:
1) Most humans recover easily from broken legs. Why can’t horses?
Jenny Hall , a famous vet , have told the Guardian that is because Horses Bones are very Light and Strong , and unfortunately, when they break, they just shatter.
In fact, it is not possible to repair the bone , not just because it is in pieces , but also if they found a way to put the pieces back together , the bone will heal bended.
2) Then why not let the horse live with three healthy legs ?
When a horse breaks one of those legs and tries to support itself constantly on the other three, the increased burden creates serious problems for the laminae at the base of those legs, the laminae will get inflamed, which is incredibly painful to the horse.
Source: The Guardian