To Anonymous User,
If the injury is caused by a locking technique, I can teach you a way to avoid it.
To make locking work, the nage must make sure that the shoulder and elbow of the uke is up.
So to render the locking technique ineffective, uke must learn to lower the shoulder and elbow, thus deny the nage the connection he/she need to make the technique work.
One simple way to achieve this is to look at your own hand, the hand that have been caught, and try to lower your shoulder by moving in towards the nage when the nage perform the technique, thus deny the nage the connection he/she need. Most aikido students will not be able to complete the locking technique when you do so especially "fighters".
They will wonder whether your arm is make of rubber or what.
To do so you are applying the non-resisting principle to save yourself by following the flow. Remember it only work, when your eyes are looking at your hand.
Try it out and find the wonder of aikido, be a lover not a fighter.
Good luck and happy new year!