Sounds awzum, can I ask what exactly you're working on, for him? A project or something? You have a link somewhere?
And yeah, it's funny you say it for I just had some problems with it today and have just decided to wear arm sling the next couple of days - just to be on the safe side. It's not breaking my arm that's the problem though, it's all about the bones in my shoulder falling apart all the time, and each time they are put back together their connection is weakened, thus making it easier to happen again afterwards. Nine times in all, have I experienced my shoulder luxated - and I feel like the tenth time is closing in :l