Sudden thumb pain

I was getting dressed one morning about 5 weeks ago, and when I was tucking in my shirt, my left thumb bent slight inward (toward my palm).  This caused a sharp stabbing pain in my top thumb knuckle which lasted only a few seconds.  I pushed my thumb inward again and experienced the same pain.  

I examined my other thumb, and it was the same way, only the pain wasn't as severe.  

After self-examining my thumbs, I noticed that any time I tried to move either of my thumbs beyond their normal range of motion, I experienced this pain.  

Over the next few weeks, I would push, pull, etc on my thumbs to try to "work the pain out", similar to the way you'd stretch a sore muscle.  

The pain has mostly subsided.

A few things to note:
1.  The pain ONLY occured when I moved my thumb beyond a normal range of motion.  Normal use and gripping caused no pain.
2.  I haven't noticed any noticeable redness or swelling in either thumb.
3.  The joints of my thumbs are not tender to the touch.  In fact, I can squeeze very tightly on the thumb joints and experience no pain.
4.  I can bend the thumb joint with no pain.  Again, pain is only present when I move my thumb beyond a normal range of motion.  Example: putting my thumb in my palm and making a fist around my thumbs.  Twisting my thumb inward or outward as if popping my thumb knuckle.
5.  About three weeks into my pain (and after 3 weeks of pulling and twisting on my thumbs trying to get the pain to subside), I noticed that both thumbs were noticeably turned outward, mostly noticeable when my thumbs were bent at the top joint.


Anyway, aside from rheumatoid arthritis, what else could be causing my thumb pain and symptoms?