How Bones Break

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Working on the climactic action scene where your protagonist lands a crucial punch? Awesome! Did they just break their arm getting interrogated by the villain? Could still be awesome, but readers might be puzzled. Superheroes and normal people can temporarily shrug off pain when the adrenaline is pumping, but broken bones are hard to use even if they don’t hurt.

It’s also worth noting that a common symptom (though not universal) of broken bones is an inability to move the affected area. Your muscles need your bones whole and in the right places to work properly. So your main character might be able to swing his arm with momentum and shoulder muscles but be unable to make a fist or hit very hard.

That’s not to say that you can’t ever have something like this in your story; straying from realism is a valid choice. Maybe there’s magic. Or aliens. Hell, maybe they thought their arm was broken, but it wasn’t.
While you may not want to get into precise medical terminology, it’s useful to know what causes (or differentiates) fractures, how they’d appear, and what restrictions they impose.

• Greenstick: They mostly affect children under 10 because their bones are softer. These fractures happen when the bone bends enough to crack, but not fully break.
  
• Oblique: Usually happen with long bones when they’re broken at an angle. Typically caused by falls or car accidents, since long bones are thick and need a lot of force to break, but can happen in fights.
  
• Transverse: Similar to oblique, transverse fractures go straight across the long bone. They have many more causes as they’re easier.
  
• Comminuted: A comminuted fracture is when a single bone is broken in a minimum of two places. These are bad breaks and often take at least a year to heal from. Like most breaks, they’re typical in very high falls and car accidents. It would be almost impossible for a human to inflict these in a fight.
  
• Longitudinal: In a longitudinal fracture, the bone breaks all along its length. These are pretty uncommon (except in professional athletes and people with osteoporosis), but can happen from crushing. Cannot be inflicted during a normal fight.
  
• Spiral: These fractures happen when your bone is twisted and looks like a corkscrew. These could happen during contact sports, but they’re pretty rare unless someone else is purposefully trying to break bones. They can be indications of child abuse in kids not old enough for contact sports.
  
• Compound: Also called open fractures, these are bad enough that the bone breaks through the skin. They look nasty and have way more risks (like infection). Think shambling zombie from your favorite scary movie. Now imagine a character hauling around that kind of open wound. It’s hard, right?
  
• Segmental: Like comminuted fractures, but worse because a segment of the bone is completely apart, leaving a gap. These are only obtained in high-velocity accidents like car accidents and high falls. Someone taking this kind of damage will need surgery and at least a year to recover.