Repetitive strain injury or as it is now known "Work related Upper Limb Disorder" is the term given to hurt to the higher limbs which is assumed to be work related thru repetitive use. This sort of injury / disorder often is affecting the wrist, forearm and higher arm.

You want to build fault for your employer or a 3rd party to achieve success in a claim. You want to show that:

1) Your companies / 3rd party should fairly have foreseen that the work they were requiring you to do carried with it a chance of injury and;
2) There were steps that the companies could and should fairly have taken which would have evaded or at the very least minimized the danger of that injury happening and ;
3) By not taking those steps, the injury has been caused.

* Claiming compensation for repetitive strain injury
1) Strength in numbers - If you're the only person experiencing the symptoms in your office and there are more folks doing an analogous task to oneself then this might suggest the cause isn't work related. If there are other folks suffering even though not to the same degree as you, if we are able to use them as witnesses to help in the case which will buttress the claim

2) improving - If the symptoms improve or stop when the job or task at work ceases, for example when you're off sick or on vacation this would suggest also the cause is work related

3) Grumbles - If you or any of your work associates have bitched to your bosses about the work that you were asked to do before the development of your symptoms then this may help your case as we'll be able to use this to show the employer could moderately have foreseen the risks of the injury you sustained.