The question you ask is complex and best left to discuss with an experienced employment attorney. My response to your post focuses only on a separate matter: the Americans With Disabilities Act. The ADA requires employers to provide employees who are disabled with reasonable accommodations that allow the employees to perform the essential functions of their job. I do not know for sure based on your post, but it seems likely that arthritis would be a disability as defined by the ADA. It appears your request, either directly or through your doctor, was a request for a reasonable accommodation. As such, the employer is prohibited from retaliating against you for making the request. The employer is also required to work with you to determine if a reasonable accommodation can be provided and determine what that accommodation will be. Additionally, it is likely that a requirement that you be “100%” violates the ADA.
I think a claim based on a request for correct OSHA approved equipment will be difficult, but it appears you likely have an ADA claim that you should consult with an experienced employment attorney about as soon as possible.