You could try a regimen of exercises that utilize a greater range and variety of motion than what you normally use on the banjo. Start carefully, and if you can, limit your playing to give it a head start on healing. You may need a serious period of rest to begin.
I had a tendonitis in my left shoulder that kept me from holding bagpipes properly for a good six months. And it's so easy to let the frustration lead you to reinjure it.
Above all get after it now, before it becomes severe enough to need surgery.
Good luck
-Glenn