Adamantium Skeleton

Adamantium Skeleton is a Fallout 3 Perk.

With the Adamantium Skeleton perk, your limbs only receive 50% of the damage they normally would.

Trivia
May be a reference to Marvel Comics superhero Wolverine's modified skeleton, or to the same trait in the Space Marines of the Warhammer 40K universe.

Taking this perk makes the enemies to mainly target your head and your torso, to lesser extend than head. Suffice enough stimpack to help alleviate this disposition.