this can be from contracted tendons - basically from being a little cramped in the uterus.
I've also seen it happen when you have given an IM needle in the back leg/rump, and hit a nerve.
Either way will resolve by itself, with time.
Either way it doesnt hurt to splint. If it makes you more confident and reassured, go ahead and splint it. I tend to leave it alone. If you do leave it, just keep an eye that the skin doesnt get rubbed raw from being on the ground all the time.