Injuries are physical traumas that surpass the ordinary loss of hit points, caused by accidents, falls and unusually heavy blows in combat. They represent breaking of bones and bone fractures, ligament and tendon injuries, organ failures, amputation, dismemberment, lung scarring and effects from disease or poison, to describe a few examples. The rule exists to encapsulate traumas to the body that would take much longer to heal than a few days of rest.
Injuries occur when a character takes 15 or more hit points of damage in a single blow. Should this happen, then 1 of those 15 damage is an injury point. For each additional 5 points of damage experienced in one blow, an additional injury point is added.
For example: Caleb the Druid falls 30 feet and suffers 25 damage, reducing him from his normal 23 maximum to -2 hit points. Of this, he receives 3 injury points of damage and 22 hit points of damage. The exact nature of the injury need not be specified, though it may necessary in future to create an injury determination chart.
Characters that have suffered an injury may heal injury points in the same way as healing hit points, except that injury points must be healed first, and it requires 10 points of healing before an injury point is removed. So, for example, after Caleb's fall, he would need 30 points of healing to remove his 3 points of injury; and then another 22 points of healing in order to restore him completely from the fall. Until such time as the first point of injury is fully healed, Caleb will remain at -2 hit points. Removing the first point of injury will heal him to -1 hit points. Once all three injury points are removed, Caleb will be at 1 hit point and thereafter can begin to heal normally.
This will mean that Caleb is quite vulnerable during this time; if he has been sufficiently reduced in hit points, according to the negative hit point rules, he may be unconscious for a lengthy time, so that his body will need to be carried until he is sufficiently healed.