My idea is that when something fractures, that whole limb is rendered useless. For example, if you fracture your left pec, you cant move that, or your shoulder, or your elbow, or your wrist. If you fracture your neck you can't move at all. If you fracture your chest, you can move your arms and your neck but nothing else, and so on.
Maybe since this is such a huge change, it can only last one turn like a DM, except it's not your whole body laxing all (except for when you fracture your neck).