I think if you want to make a more realistic health system like in Dwarf Fortress you should start by making multiple hp pools. Tissue > Muscle > Tendon > Bone.
And maybe add pain to the game, something like a pain threshold based on endurance and intelligence (Willpower). Someone with a pierced muscle will do less damage since his muscle can't properly work. But like in Dwarf Fortress when you attack someone each weapon should have different abilities. Maybe you could have daggers that do little damage but most of the damage is done internally.
Lets say you have 100 tissue hp, 50 muscle hp, 150 bone hp. and 10 tendon hp Then depending on the weapon they get a % to bypass the first tiers of natural armor. Swords and axes doing slashing damage does mostly tissue and muscle damage, while a hammer would harm the bone pretty much every time, but it still hurts the tissue and muscles slightly. And instead of a critical strke that simply does more damage you could make critical strikes hit tendons or maybe bypass more tissue and hit directly depending on where are they aiming.
Some examples for injuries.
Damage is reduced by the % of missing hp on the bone of a limb. If your arm is shattered you shouldn't be able to attack with full force, now when its broken you can even do anything without screaming in pain.
Speed attack reduced by the % of missing hp on the muscle. The only thing that lets you move your arms are your muscles, and if they're cut in half you can't expect to move your arm like nothing happends.
Now tendons are more of a lucky strike, if you cut that you're making someone unable to move his arm at all, Pretty hard to hit unless you're either skilled and now where to aim, or just lucky when you swing your axe.
As for armor threshold it could work based on the % of the missing hp. The more tissue you lose the more chances to hit the muscles and the bone.
Not sure how hard this would be to implement, but it's mostly math and numbers.
But then you could also have something like this.
Head - Tissue - Muscle - eye - eye - skull - brain
Upper Chest - Tissue - Muscle - Ribs - Lung - Lung - Hearth
Lower Chest - Tissue - Muscle - Stomach - Kidneys - Guts
Groin - Tissue - Muscle (Pain x3)
Legs/arms - Tissue - Muscle - Bone - Tendon
Cut eye = -30%-ish accuracy loss.
Pierced lug = -50% stamina regen
Pierced stomach = Lots of bleeding
Pierced Kidney = Pain + blood
Pierced guts = Pain + pain + blood.
Also having internal organs hurt should automactly cause internal bleeding (Which i seen in the game very rarely).
Another way to see it could be the way Rimworld uses bodyparts. For example you have two eyes that gives +50% accuracy each. If you lose one, you lose the bonus from the eye. (Which was also easier to implement having extra eyes and they already had bonuses). So instead of implementing a system where you have to give a malus to someone based on every part that is hit, you give them a bonus based on which parts they have. And from there the more parts, the merrier.