Board Thread:Boruto Discussions/@comment-1458758-20171229124917/@comment-1458758-20171230120710

Sadly, we don't know at the current the circumstances. The series is quite vague about that. It seems Katasuke as a doctor was the one to save Ao back during the war, but since Ninja Tech wasn't really a thing back then, we can assume his new limbs and such are more recent additions which might be down to Kara's influence.