Hi Aimee-

   It’s a thumb (or finger) that cannot be straightened out completely. Bend the outer digit of your thumb at a 90 degree angle in towards the palm of your hand and then keep it that way 24/7- that’s what Kate had going on. With kids, it’s usually due to a knot in the tendon/ligament (bah I forget which) that gets caught up on the surrounding muscle so that the thumb/finger can’t fully extend. I’m pretty sure that’s how it goes (haha- I’ve read up too much on CAH and not enough on the other nutty things Kate has) 

   My husband and I have a bad sense of humor- we called them her monkey thumbs until we got them fixed!

Martha