I've been in and out too...am trying to catch up. I had a much better example, but I lost the link, will keep looking. The thumb can be in a different position...the back of the hand is arched so the top of the palm sticks out a little bit. If you can figure out the proper form, it changes the position of the thumb.. the sketch I posted was CLOSE, but not exact. Here's another example..but I"m still looking for the better one. I think it was valpal1 that brought this up before...I wish I would have bookmarked where the other sketch was. I *thought* they were on the same website. Here's one to take a looksee at. If the hand or wrist is manipulated by a 2nd party, say by restraints or whatever, the thumb could be manipulated even further.
Only problem is, if my memory serves me correct, I counted six uniform abrasions in this semi-circle. Where did you get the illustration from?