Ibuprofin is about as good as you can get for an over-the-counter anti-inflammatory drug. Alternate between cold and hot to reduce the swelling at a faster rate.
I doubt that it's arthritis that you have. Arthritis is a gradual, degenerative process... it doesn't just show up "all of a sudden." Sounds to me like you accidentally jammed the finger somehow, possibly forgetting when and where, or possibly even during sleep.
I know all about having arthritis in a left-index finger. I had my left hand pulled into a bag-making machine 15 years ago and it crushed the joint of my left index finger and also broke the finger in 3 (other) seperate places. My middle finger was broken in two places.
Imagine that...
One day I could copy any lick Jimmy Page or EVH ever did, and the next day I was told I would probably never play guitar again. Fortunately, due to surgery, I have regained about 75% usage of my left index finger and the middle one is 100%. That's not too bad, considering that I couldn't even pick up a guitar for over 2 years after the accident.
On the upside, though, I bought a set of drums and taught myself to play them after a year of feeling sorry for myself... so it wasn't a total loss that this happened. Holding the drum sticks helped me regain hand strength, too... which quickened my recovery. Anyway, I now suffer from arthritis in my left index finger. Sometimes it gets pretty painful during quick, drastic changes in temperature or a drop in barometric pressure. I can tell you when it's going to rain an hour or two before it actually starts.
If you are
extremely worried about your playing ability for your gig, find someplace in your area where they will lend or sell you a "TENS" unit. I used one during my therapy 15 years ago (when it was cutting-edge technology) but I believe they are used quite commonly now. It's basically a little electronic unit that sends a small electrical charge to an injury, easing the pain and instantly increasing mobility. You put on some goopy gel, attach the little pad, and VOILA!... instant pain relief.
At the very least, take two "Aleve" tablets just before you play. That stuff works wonders!
Hope this helps a bit.
Good luck with the gig!
