You suffer a lingering wound whenever you receive a critical hit. Only critical hits can cause a lingering wounds, and critical hits do not cause any extra HP damage (unless specified by another ability). When you suffer a critical hit, roll 1d20 to see what breaks: 1-3) Left Leg; 4-6) Right Leg; 7-9) Left Arm; 10-12) Right Arm; 13-18) Torso; 19-20) Head. A broken leg reduces speed by half, a broken arm cannot be used to carry anything, a broken torso requires a check to do anything, and a broken head is a KO.
Interesting. I would not have foreseen that. That is definitely not the intent.This will have the overall effect of making your campaign a lot more deadly since the PCs will be exposed to way more crits over the course of your campaign than your monsters will ever be. It also makes lower CR monsters quite deadly. My character was crit 3 times in 2 rounds last session, this rule would've basically killed him outright.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.