make sure you're holding your poles the correct way. my thumb got so bad i ended up just taking the wrist strap off on my right pole. another thing to look into are the goode pole/glove system. really gay, but a lot safer.
yea, i dislocated mine when i fell 5 weeks ago. Now i wear this brace thing. Was in a cast for 4 weeks and now the brace. At least i didnt need surgery. I guess its pretty common though.