One of my characters has hands very different to the ones we're used to.
His fingers can close towards both sides of the hand, meaning that the back of his hand is also a palm and he has a second opposable thumb on the opposite side of our regular thumb (between the little finger and the wrist)
Would this hand setup require major muscular changes? Note that this is a natural trait from his species, not a result of surgery, genetic accidents or magic.
Also, would this different kind of hand be any more functional than regular hands? I tried to design them as a way to make this character more skilled and versatile when manipulating various objects, ranging from a big lance to very small pebbles (and as a way to make the character novel).