Modern technology can do many things. At least you would think all the rich folks connected with horse racing would pitch in do fund research on safer track materials, better cushioning material in racetracks, and so on. They don't even try. That's my problem with them.
As for injuries to the hind legs, they do happen more than you may be aware of, but it's true that the front legs are more likely to be injured.
That may be. I watch horse racing pretty regularly and I just hardly ever see it happen.
Beyond that, sore horses (primarily gelded claimers) are raced all the time. It makes me sick.