User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-6068707-20130714151153/@comment-3146930-20130714152241

Percy would need some water to do that. There is also no garenty it would work on broken bones, as most of the time he uses water to heal surface wounds (cuts and such). I mean he didn't really seem to be able to heal Annabeth when she was poisoned by Ethan, so maybe there are things he can and can't do, or just he can only help to a limited degree. He isn't a healer after all.