I agree with tinyliny about this horse.
But, as far as horses being over at the knee....this is what I was always told. Over at the knee is better than behind at the knee. Many TB racehorse are in fact over at the knee. I was told they breed them purposelessly like this due to the have a better break over, and it helps them really get up and go. My horse is over at the knee, and Im sure many horses are over at the knee, and they can be perfectly sound, granted that's their only conformational issue.
Also, as far as being sound...there was a horse at my school, he was over at the knee, sickle hocked, toed in, his cannons were far too short, horrid angles, just the ugliest conformed horse that I have ever seen. Someone bought him for a trail horse, not only does he love it, but he is 100% sound for trail riding....
Not sure if that helps or not, maybe someone with some more insight can help you out on the topic!