I've Been Giving My Dog Prednisone For 3 Years. Its

I've been giving my dog prednisone for 3 years. Its for knee problems and possible spine problems. I give her 1/4 of a 5mg tablet every other day. The specialist told me that it shouldn't hurt her in the long term. Now she is getting bad cramps in her front legs which I can bend back and forth several times to relieve the cramps. Could this be caused from the prednisone? Possible Cushing Disease?