A friend on mine bought a Paint horse with very short, upright pasterns. She bought Max when he was 3, by 4 1/2 she was already having soundness issues. Max was diagnosed with bone spurs on his navicular bone that was directly linked to his pasterns. She did shock wave therapy, then ended up having him nerved when that didn't help. It was very sad to watch his decline, and all the money she put out trying to fix him. In the end, she had to put him to sleep at 8 years old last summer due to his bone spurs becoming so bad they ended up lacerating the tendons in both front legs.
Max was an extreme case, and I don't mean to scare you with this story...but it has made me paranoid about pasterns now. His mom has basically the same length and angle in her pasterns and is 26 years old now and never lame a day in her life, so it really depends on the horse.