What is this?

If you are a person who gets on the computer, or has a PDA, or owns a handheld video game system like Game Boy, Gamne Boy Color, Game Boy Advance SP, Nintendo, Nintendo DS, etc. Have you ever felt the joints in your thumbs jam so you couldn't move them a certain way?!?!? I have this problem and I would like to know what this is and how to fix this problem. Please help me. Thanks Pce -Becca