A Stab in the Arm: How a Knife Interacts with Your Body
By Michael Dinowitz and CFEditor
As writers, we're often called upon to write scenes in which knives are thrown or weapons are swung. Yet how many of us have thrown a knife or studied the types of wounds that can occur when a knife strikes? In this article, we'll discuss some of the basics that will help you write a realistic fight scene where your character gets hit by a knife.
The Thrown Knife: How Does it Hit?
When a knife is thrown at someone, four different types of wounds can result from a successful hit. These wounds assume that your knife is a standard dagger with a sharp point, two sharp, bladed sides, and a hilt. Other knives or thrown knife-type weapons can act in different ways, which we won't cover now.
Point of blade leading: The knife cuts through whatever it impacts.
Side of blade hits the body: The blade will slash the point of impact, will rarely, if ever, stick, and will most likely just fly off to one side.
The flat of the blade hits the body: This will cause almost no damage, the knife will be deflected off, and you can laugh at the thrower for being a worthless knife thrower.
The hilt can hit the body, possibly causing a bruise: See laughing at knife thrower above.
The damage all depends on the knife-thrower's skill, the type of knife being thrown, the ability of the target to dodge, and a few other factors that are not really important except for literary detail. In addition, what is between the knife and where the knife hits is very important, and will be discussed later.
The Effect of Knife Penetration
A knife going point first into a body will really be hitting one or more of the following places: an internal organ, a bone, or a muscle group.
Internal Organs
If an internal organ is hit, then you're in deep trouble, because a knife will slice through that organ and cause you massive internal injuries. Even a thin slice against an internal organ can be deadly. A lung could collapse, a heart could be damaged, kidneys could be perforated, etc. The only place you can really take a knife and not be in deep trouble is the intestines. (If you're sliced across your belly, the intestines may spill out.)
In most stories, when we're talking about a knife, we're talking about one that is being thrown and hits the upper body, specifically the upper arm and shoulder area. This avoids almost all of the problems that come from internal organ hits and restricts the type of damage to bones and muscles.
Bones
A knife that hits a bone can either become embedded in the bone, can cut through the bone, or crack it. If the knife blade hits parallel to the bone, then the crack will probably be straight down the length of the bone. In such a case, the knife has a good chance of becoming stuck.
If the knife hits perpendicular to the bone, it can crack the bone or even slice right through it. A perpendicular knife strike rarely becomes embedded in the bone, because the knife is usually as wide or wider than the bone. This, of course, depends on the type of knife, as a thin stiletto, an ice pick, or even a sharpened screwdriver, can be smaller in width than the bone that it is hitting.
Muscles
When a knife hits a muscle, the same question of parallel vs. perpendicular comes up. A knife hitting parallel to the muscle will encounter very little resistance, as it is slicing inline with the muscle fibers. If the point of impact consists only of muscle, a parallel strike could easily put the knife completely through the muscle, with the point sticking out of one side of the muscle and the hilt out of the other. (This is usually a bicep or upper arm hit.) Pulling the knife out of this type of wound will cause very little additional damage, as long as it is pulled straight out. If a knife embedded in this way is rocked back and forth, it will slice more and more muscle and may even result in the muscle being severed. Healing from this type of wound will be faster, have less complications, need less professional help, and will rarely result in any long-term or permanent damage.
If your badass character gets stabbed, having the knife go in this way will allow her to pull it out and bandage the wound easily, or to just leave it in and drive off on her motorcycle (if she's a true badass). I would not suggest doing so because any jostling of the knife will slice through more muscle along the same parallel lines, exacerbating the damage.
A perpendicular knife strike is bad news because it is literally slicing through the muscles, severing the muscle fibers themselves rather than going between them. It is possible to literally cut through the entire bicep and make the arm totally useless in this manner. Perpendicular wounds are hard to sew up, heal very slowly, and require that the damaged muscle not be used while it is healing (if it can heal at all). This type of wound requires a real surgeon or magical aid to heal (if such a thing exists in your story).
A few notes about hits to this area:
Any breaking of the collarbone is massively painful and removes the character from the story for a while. The pain is so great that the chance of causing unconsciousness is very high.
The upper arm contains the most muscle mass, so it gives the most dramatic place to cause a wound without the wound description being unrealistic and/or removing the character from play. Stabbing someone through the bicep, tricep or deltoid muscles will allow them to have damage, show the damage, repair the damage, and still be usable the same or next day (unless, of course, you have a perpendicular wound).
The upper chest/shoulder area also has a muscle mass but behind that mass is internal organs, making a strike there potentially more upper back/shoulder area will have very little muscle mass to hit and there is a high chance of hitting an internal organ.
All of this, of course, depends on the depth of the cut. A thin slice across a body part will cause more bleeding and scarring than actual damage. A stab, on the other hand, which has a depth of a quarter inch or more, is something that is a lot more serious, because it affects one of the three groups mentioned above. The density of any muscles being hit will have an effect as well, giving resistance to the strike and reducing penetration.
Penetration and Clothing
The best way to reduce penetration is to have your character wear some form of armor. But don't worry, because we're not talking medieval armor; we're talking things that you can and should wear today.
A heavy dungaree jacket is probably the lightest type of armor you can have, as long as it's not the lighter fashion type that most people wear. In older movies and stories, motorcyclists and others who need to protect their body from skids will wear this type of jacket. As most badass characters are trying to emulate these types of bikers, heavy dungaree is a good option.
Along the same lines, a tweed jacket will give much of the same protection but you see very few tweed jackets on badass motorcyclists (except in Buffy).
If you don't have access to a thick jacket, having multiple layers of clothing can also give you some protection against penetration.
The ultimate in light armor is a true leather motorcycle jacket. I say "true" because most leather jackets are made of thin calve skin (what they use for women's leather pants) or something similar, which is actually less protective than a dungaree jacket or even a suit jacket. True motorcycle leathers are thick, heavy, and are designed so that if you are traveling on a bike at high speed and you fall off, when you skid, the fifty feet or so that you travel will be covered by shredded leather, not shredded skin. Such a jacket will not necessarily repel a knife, but can greatly reduce the depth at which the knife will enter the body and, subsequently, the amount of damage it will cause. If the knife does not hit a leather jacket directly with the blade point, there is a chance that the knife can be deflected. A bad throw against a leather jacket is as bad as no throw at all. The only down side is that a leather jacket of this sort can be stiff and encumbering, slowing down your character's movement. The only solution to this is for the character to wear the jacket on a semi-regular basis, getting her body used to it, and causing certain points, such as the joints, to be softer. A new leather jacket is akin to a straightjacket for the first couple of days.
(This article is based on normal motorcycle leather jackets and not on some of the newer, high-tech motorcycle "armor" that is available today. A very modern hunter is truly a dangerous foe. And we're not even talking weapons yet.)
The bottom line is: If you expect your character to be stabbed in the arm, shoulder, or even the chest or back, what she's wearing can save her life and make the story much more detailed.