Hi George. Welcome to the forum!
I'm not familiar with arthritis symptoms...YET
But I am finding it increasingly difficult to give my fingers that "stretched out", "loosened up" feeling. I'm only 55, but I've taken a hint from a much younger pianist (at the time he was young).
Glenn Gould used to soak his hands and forearms in warm water for about 20 minutes before playing. I try to do something like that myself. I wash my dishes by hand. That takes about 5 to 10 minutes. Otherwise, I hold my hands under warm water for just a little while until they feel warm and loose before I go to the guitar.
It REALLY helps! I feel like I've already done my warm ups.
There was a recent thread about your question. Someone suggested using one of those warm packs that you put in the microwave. Good idea, because you don't have to put your hands in water so long that they get pruney...
Hope that helps,