Re: Aikido injuries
"Shoulder separation" --dislocation between the collarbone and the top of the sternum--is a common and usually self-inflicted beginners injury in aikido, when folks trying to do forward rolls accidentally project themselves directly on the top of the shoulder. If there are a LOT of these it may mean that the instructor is simply not focussing on teaching small low on-the-ground rolls or may be encouraging faster progress than they are ready for.
Tearing ligaments forearm ligaments should not be a "common" injury. But as others have said, it would be good to get verification from more than one source.