Glr: It means, mudhead, that your bones cannot be broken.
Not everyone can have a body that's Nigh-Invulnerable. So, what's the next best thing for creating a character who is highly resistant to injury? Why, giving them bones that can't be broken, of course. The character will still bleed and bruise, and will still be vulnerable to a slit throat, or a stab to the heart, yet will be immune to any number of potentially crippling injuries. From a storytelling perspective, this can be the best of both worlds, providing a character who can justifiably shrug off incredible beatings, while still being in a believable amount of danger from most weapons.
How their bones became unbreakable can vary. Perhaps they were surgically reinforced or altered. Perhaps they were bonded with, or even replaced with, metal. Perhaps the character is a mutant, and bones with the tensile strength of titanium are simply a part of his or her natural makeup. This trope is most often seen in science-fiction settings where mutation, genetic engineering, or advanced surgical techniques can justify its existence, though it can show up anywhere.
May be a trait of the Cyborg or Super Soldier. Might be combined with a Healing Factor to create a truly unstoppable warrior. See Super Toughness and other Nigh-Invulnerable subtropes for when it's the entire body and not just the bones that are this hard to damage. Not to be confused with I Am Big Boned.
- In Naruto, the Kaguya clan have bones that are as tough as steel as their Bloodline limit, and on top of that they can actually grow extra bones at will and use them for a number of squicky effects like growing new bones out of their skin and using them as bladed weapons, covering their skin in bony armour, or even summoning an entire field of spiky bones. As a result, the body-swapping villain Orochimaru brought the last survivor of the clan- Kimmimaro- into his cult and trained him as a ninja, hoping to use him as his next host; unfortunately, unbreakable bones don't stop you from getting tuberculosis and instead, Kimmimaro tragically opts to die fighting for the guy who basically brainwashed and no longer has any use for him.
- Daredevil nemesis Bullseye had adamantium applied to parts of his skeleton and spinal column after one too many defeats at Daredevil's hands.
- In his backstory, Spider-Man foe Hammerhead had his skull replaced with a strong steel alloy after he was attacked and left for dead in an alley. His skull is so strong it can withstand punches from Spider-Man and burst through brick walls. Later, Mr Negative had Hammerhead's entire upper skeleton replaced with adamantium after he was shot.
- In IDW Publishing's 2005 Transformers continuity, Overlord and other Phase Sixers underwent a process to reinforce their endoskeletons with ununtrium, rendering them virtually indestructible. In Last Stand of the Wreckers, Overlord gets shot full of bombs and vanishes in a huge explosion, only to emerge moments later as a burning, angry, still mostly-intact skeleton. The only thing that can cut through ununtrium is more ununtrium, the last of which is thought to have been used up on Overlord. The Decepticon Justice Division possesses the only known ununtrium-infused weapons, letting them cut down rogue Phase Sixers.
- Wolverine himself is probably the most famous comic book example, having had the nigh-indestructible metal known as adamantium bonded to his bones during surgery. It's sometimes noted by authors that adamantium is a heavy metal and therefore toxic, and Wolverine's Healing Factor is the only thing keeping him from dying from heavy metal poisoning (which becomes a serious problem in instances where he loses his powers). This issue is ignored when it comes to characters who don't have a healing factor like Bullseye, Deathstrike, or Hammerhead.
- Wolverine's foe Lady Deathstrike believed that her father's process for bonding adamanitum to bone had been stolen by the people who created Wolverine. To gain revenge on him and claim his skeleton, Deathstrike had herself rebuilt as a cyborg, complete with her own adamantium skeletal structure.
- Several of Wolverine's major enemies, including Sabretooth and Romulus, have, at various points, had adamantium infused into their own skeletons, though they have rarely kept it.
- Avatar briefly has Colonel Quaritch mention that Na'vi bones are reinforced with naturally occurring carbon fiber, with the implication being they're more resistant to breakage than human bones.
- Hugh Jackman's portrayal of Wolverine in the X-Men Film Series has the same unbreakable adamantium bones as his comic book counterpart.
- The Cobra Trilogy by Timothy Zahn features super soldiers whose bones are engineered to be unbreakable as part of their conditioning. Though in a catch, the process causes them to develop arthritis and anemia later in life.
- One criminal in the Judge Dee series used his thicker-than-average bones to his advantage in fights but claimed to be haunted by bad luck throughout his life. Although there was a sizeable amount of Never My Fault in his Motive Rant, the judge's lieutenants can't help but see his point when the executioner has to chop at his neck two or three times before it finally takes due to the man's strong bones.
- Last Legionary has protagonist Keill Randor whose bones were surgically replaced, molecule by molecule, with an incredibly resilient organic alloy as part of an attempt to save his life from the radiation sickness that had settled into his skeleton. This, coupled with his Legionary training makes him a veritable One-Man Army. In an interesting contrast, his archenemy, The One, is a crippled dwarf in a suit of Powered Armour.
- Parahumans in The Pride of Parahumans have titanium alloy skeletons to prevent microgravity-induced osteoporosis, and it has the side effect of making their bones very hard to break.
- Roxanne Furst, the titular heroine of Roxy Was Here, has bones that naturally convert into a unique, unbreakable golden metal. Being a lifelong comic book nerd, she of course names the metal Adamantium.
- In Christopher Ruocchio's The Sun Eater, after coming back from the dead, protagonist Hadrian Marlowe finds that his severed left arm has been regrown by a grateful Kharn Sagara (Hadrian protected Sagara's clones during a brain upload when Sagara's old body got murdered). As a little extra, Sagara had the bones of the regrown arm replaced with an adamant alloy, a substance so densely woven that even single atom-edged Highmatter blades can cut it.
- Uglies: The Specials are super soldiers with aircraft metal in the place of their bones, alongside numerous other body modifications.
- In early seasons of Smallville, Clark isn't fully invulnerable as his powers are still developing, i.e. while bullets bounce off him they do leave serious bruises. However, while his soft tissues can be harmed his bones are explicitly unbreakable.
- Cyberpunk 2020:
- Applying TuffBone cyberware skeletal enhancement to a person makes it more difficult to damage their bones.
- Bone Lace uses nanotechnology to wrap the skeleton in a weave of metal and plastic threads, making them stronger and thicker. This increases its ability to absorb physical damage.
- Gamma World: The Skeletal Enhancement mutation increases the strength of a creature's bones, causing them to take less damage from attacks.
- Shadowrun: The cybertechnology technique called bone lacing uses metal and plastic to increase the strength of the subject's skeleton, making it more resistant to injury.
- Warhammer 40,000:
- Space Marines have their bones coated with ceramite to harden them against most injuries. They also have their ribcages solidified into a single block so that no weapon can slide between their ribs. Their evil counterparts, the Chaos Marines benefit from the same modifications and may have their toughness further enhanced by deals with the Chaos Gods.
- Tyranids have naturally tough bones which, when sharpened, can serve as bladed weapons. They can also reinforce the Tyrannids already tough carpaces.
- The Fallout series features a perk called "Adamantium Skeleton" which massively reduces limb damage. The Fallout 4 iteration allows for the perk to be upgraded to entirely eliminate limb damage and prevent the player character from having their limbs crippled by enemy attacks, although the legs are still vulnerable to crippling caused by fall damage. It also doubles as an obvious Shout-Out to a mutant famously known for it in particular.
- Spartans from Halo have "carbide ceramic ossification" as part of their Bio-Augmentation package, which gives them something to this effect. It's the main reason they can use their Powered Armor, which is otherwise literally too strong for humans to use (a poor Red Shirt who tried out a prototype ended up shattering every bone in his body).
- Genocide Man has the Genocide Men whose bones are hardened via the implantation of ceramics. The process needs hardy skeletons to begin with, however; when applied to Lola, who had Osteoporosis at the time, it just made her cripplingly brittle.
- Unsounded: Elka has a pymaric implant designed to make her bones harden or soften to prevent their breakage in response to their being hit with pressure. This helps explain why Toma came out of their waterfall jumping escape with more damage than her; her bones temporarily adapt to things that would otherwise break them.
- SCP Foundation: As detailed in the interview with the captain that captured it, SCP-096's skeleton is, at the very least, extremely durable through anomalous means. Its ribcage remained in perfect condition even after it sustained a direct hit from an anti-tank gun.
- A Connecticut family were found to possess a mutation that results in significantly higher than usual bone density (to the point that they were as tough as granite). No one in the family has ever been reported to have so much as fractured a bone. Unfortunately, these people are also unable to swim, since their increased bone density leaves them unable to float.
- The Hero shrew, whose specially reinforced spine and ribcage allow it to survive being stepped on by a human (the equivalent of a human being stepped on by ten elephants at once).