This mod have 2 basic types of injuries: Bleeding and Fractures.
If you are just hit by a monster or another player, there is a chance of getting bleeding state (the more bleeding states you have, the quicker will your health bar go down).
But if your health is reduced by a special damage, such as an anvil falling on your head, or jumping from too high, you have a chance to get fracture state. Every fractured part of your body will add different negative effect, like slowness for legs or mining fatigue for arms. All these injuries can be seen in gui which is binded on keybind. (see the picture)