Robin,

Captain has a problem with his back leg, usually after he has RUN AND RUN AND RUN ......... but sometimes, simply when he gets up from lying down.
I have Rimadyl in my cupboard that I give him every now and again, if it hurts.
BUT initially, he was on it for approx. 1.5 weeks - then I was instructed only to give it to him if it hurts.

Captain NEVER, EVER yelps, but when I took him to the vet, they poked and prodded him, until he "yelped"
We had X-rays, blood tests, and a VERY EXPENSIVE muscle test done on Captain when it started .......... only to establish, that they cannot find ANYTHING wrong, and that it might be muscle strain.

I hope that is Katie's problem too

Kisses to Katie
Michelle