Merlotgran,
When I was diagnosed with RA in my early 40's, my consultant contradicted advice from various medics, that I should stop riding. His advice was to ride as long as I could "but don't fall off, that would be very bad in your situation"
I finally stopped in my late 50's, after the huge horse I was riding shifted his rear end slightly as we went through a gate. My left osteo arthritic knee was the size of a rugby ball by the time I got home. I struggled to get the jodhpurs over the knee then iced said knee. Like merlot, by this stage if I missed riding regularly, I'd be so stiff when I resumed. I decided the big horse and the gate post were telling me something. Mind you, if I was Her Majesty, I hope I'd have a bomb proof Fell pony to wander my estates on. Fabulous.