The Science of Slicing

Tgace

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Everything youd want to know about knife wounds:

Langers Lines:

If a stabbing with a knife is "straight in and out" then the length of the stab wound on the skin surface is typically slightly less than the width of the blade, due to the elastic recoil of the skin following withdrawal of the weapon. This effect is exaggerated by the tendency of the wound to gape open so that the wound becomes wider but shorter; the extent of gaping reflects the alignment of the wound relative to natural lines of tension within the skin - Langer's lines. Wounds with their long axis parallel with Langer's lines tend to gape only slightly, whereas wounds aligned at right angles to Langer's lines tend to gape widely. The extent of wound gaping is also influenced by damage to underlying fascia and muscles. Consequently, the length of a stab wound on the skin surface should be measured after the gaping edges have been approximated (using transparent tape), thus re-establishing the anatomical relationship of the skin edges that existed prior to injury.

So if Im reading this right, cuts perpendicular to these lines will be wider than ones parallel to them correct?
 

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shesulsa

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So if Im reading this right, cuts perpendicular to these lines will be wider than ones parallel to them correct?
That's how I read it.
 
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Tgace

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Now from what Im reading, these "lines of clevage" have to do with skin elasticity and are used by doctors to determine the best way to cut so as to minimize scarring.

So if you look at the lines like strings... if you cut across the strings you get more resistance and a larger frayed slice with a a lot of "ends" flapping about. Now if you were to cut "between" the strings wouldnt you meet less resistance and be able to slice deeper? It appears that if you were to slash against these lines the wound would be larger and "uglier" but allong the bellies of most muscles which IMO wouldnt assure loss of function as well as cutting across the belly which would sever more muscle strands. Does that sound logical?
 
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Tgace

Tgace

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Or maybe Im wrong on that....

http://www.vard.org/jour/99/36/2/edsberg.htm
There are also directional effects of skin, which are explained by Langer's cleavage lines (15-18). The stress-strain relationships in uniaxial tension show skin to be stiffer along Langer's lines than across the lines. As a result, skin incisions perpendicular to Langer's lines gap more than those parallel to the lines.
 

Kenpodoc

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Tgace said:
Now from what Im reading, these "lines of clevage" have to do with skin elasticity and are used by doctors to determine the best way to cut so as to minimize scarring.

So if you look at the lines like strings... if you cut across the strings you get more resistance and a larger frayed slice with a a lot of "ends" flapping about. Now if you were to cut "between" the strings wouldnt you meet less resistance and be able to slice deeper? It appears that if you were to slash against these lines the wound would be larger and "uglier" but allong the bellies of most muscles which IMO wouldnt assure loss of function as well as cutting across the belly which would sever more muscle strands. Does that sound logical?
Surgically, in my experience it's equally easy to cut across or with Langer's lines it just affects the scarring. The amount of gaping is minimally different and not significant compared to other aspects of knife or chainsaw injuries. If you want to maxamize gaping make big deep cuts. Cuts to the extensor surfaces gape more and scar worse. The cut levels that affect function are far below langers line's.

Jeff
 

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How far, would you say? and can you comment on flesh compression in situations of pressure/puncture?
 
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Tgace

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Cool, someone with "carving" experience. ;)

So from your experience,just how easy do you think it is to impair motor function with a knife strike? Will slashes to the biceps/triceps/tendons etc "easily" render the arm useless or is it more difficult to cut that deeply with a slash? Does it require pretty much a complete severing of the muscle or is there a percentage of damage that will render the muscle useless.
 

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shesulsa said:
How far, would you say? and can you comment on flesh compression in situations of pressure/puncture?
It takes a fair amount of compression to cut, puncture skin more than superficially. Obesity, skin resiliance and skin mobility all factor into a difficult equation. Even with a sharp scalpel you need to hold tension on the skin to easily cut deeply. Dull scalpels take more work.

Tgace said:
Cool, someone with "carving" experience. ;)

So from your experience,just how easy do you think it is to impair motor function with a knife strike? Will slashes to the biceps/triceps/tendons etc "easily" render the arm useless or is it more difficult to cut that deeply with a slash? Does it require pretty much a complete severing of the muscle or is there a percentage of damage that will render the muscle useless.
Muscle cuts cause increasing disfunction relative and proportional to the percentage of the muscle cut. Tendons must be fully cut to cause dysfunction but partial cuts render the injured tendon more at risk for spontaneous rupture. I've had farmers spontaneously tear through 2/3 of their bicep and finish their work before coming in for evaluation. I've never been in a knife fight but from the injuries I've seen would guess that it is difficult to disable an arm with a single slash of a knife. I've seen arms with multiple defensive wounds and found the person still able to use the arm when I evaluated them. The deaths I've seen from knife wounds have all been due to stabs. As to how difficult it is to disable an arm with a slash, that probably depends on the size and sharpness of the knife. 3 inch blades will require more work to disable an arm then a slash with a Kris.

Jeff
 
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Tgace

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Interesting. I hear a lot of knife instructors talking about "defensive" use of the blade and slashing at the arms and legs to cause dysfunction so you can escape more easily. My problems with "less lethal" use of the blade aside...Ive never cut a human being but from cutting up big game Ive always thought that slashing attacks that could cause that kind of damage are easier said than done with any type of blade a person would usually be able to carry.
 

Makalakumu

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Tgace said:
Interesting. I hear a lot of knife instructors talking about "defensive" use of the blade and slashing at the arms and legs to cause dysfunction so you can escape more easily. My problems with "less lethal" use of the blade aside...Ive never cut a human being but from cutting up big game Ive always thought that slashing attacks that could cause that kind of damage are easier said than done with any type of blade a person would usually be able to carry.

I've trained a little in pekiti tersia and I've gone to a seminar by Tuhon Bill Mcgrath. At the seminar, he focused on knife work using the blades we carry with us every day...under six inches. Basically, he took the whole concept of "defanging the snake" to task. He said that many arnis techniques are predicated on the use of a larger knife and that a smaller knife just isn't going to do the same.

In his words, as he held out his own folder, "this is not a sword."
 
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Tgace

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I would have to agree. Have you ever seen the episode of "Cops" where the police are following a knife wielding man down the highway, whacking away at his hand and arm with their batons and he didnt drop the knife? Eventually he was shot when he came at an officer. While I do not discount the concept, I dont believe it should be depended on.
 

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Kenpodoc said:
It takes a fair amount of compression to cut, puncture skin more than superficially. Obesity, skin resiliance and skin mobility all factor into a difficult equation. Even with a sharp scalpel you need to hold tension on the skin to easily cut deeply. Dull scalpels take more work.

Essentially the idea behind the "pressure cut" techniques of Pekiti Tirsia Kali, wherein wrist or wrist/knife or wrist/butt of stick etc. provides a platform or fulcrum for the knife in the other hand to cut across the arteries and/or tendons of the opponent's wrist. These occur a lot in the Pekiti Tirsia Espada y Daga Contradas, for example, that Tuhon McGrath taught in his 2004 seminar series in Fishkill, New York.

With respect to the "Cops" episode: the guy was hit in the forearm with the officer's ASP baton. I suspect that the fleshy part of the forearm was struck - but even if bone was hit (and broken) the guy could have been high enough, drunk enough, or emotionally disturbed enough not to register the pain. A direct hit to the ulnar nerve that compressed and shocked that part of the nervous system would probably have rendered the arm unserviceable for a while - but that didn't happen.

A deep cut to the muscles in the forearm that help the fingers close around the handle of the knife will often render someone incapable of holding their weapon, but as per the previous posts above, this doesn't often happen with a 4" knife. Cuts/slashes with this kind of weapon can serve as deterrents especially if applied to the fingers, but would probably have to be followed up by the kind of pressure cuts described above or thrusts to vital areas if the opponent refuses to be deterred.

For those of you that watched Rome his year: Pulo did a nice job "defanging the snake" in the arena during the penultimate episode when he disarms his opponent using something very similar to a Pekiti Tirsia Kali espada y daga contrada.

Best,

Steve Lamade
 

Makalakumu

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One of the points that Tuhon McGrath made in his seminar is that one can still defang the snake with a small knife. The technique has to change though. He holds his folder in a reverse grip with the blade facing backward. Then he'll pound the knife in and rip it out by pulling backward. The basic reverse grip knife set he taught us has many of these techniques in it.
 

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I'd like to add a couple of points to what I said earlier. My experiense with knife wounds is medical not as a knifer but I suspect the information is still useful.

Most peoples experience cutting tissue is either accidental or with animals post mortem. After death the tissues solidify and the feel and response to the knife is very different than pre mortem. Living tissue is harder to cut than dead tissue.

Cuts in living people are messy and that changes everything. Even superficial cuts bleed profusely and make everyone slippery. I've seen people fall in operating rooms and ERs because of the blood. Furthermore the tissue becomes difficult to stablize secondary to the slick coating of fresh blood. (older blood is sticky.)

When Living fatty tissue is cut it oozes oily liquid (think Wesson Oil.) This makes things even more slippery. The effect is far more dramatic than most people imagine.

The psycholgical issues are more complicated than Most people imagine. I've watched Law Officers and experienced Military people pass out watching operations and autopsies. Most people cause hesitation wounds the first time they try to cut even an anesthetised patient. You can train yourself to get by this but I'm not sure that it is good for people in other ways. Medical School involves a certain amount of brain washing which is essential but probably not good for the recipients. The majority of the WWII patients I've had who were frontline soldiers never fully recovered from having to kill others and deal with the death and destruction. Most remained good men but haunted by what they felt they had to do. Generally the men who talked most enthusiastically about killing were never in a position to have to do so.

I do train with knives but fear the reality. The training is fun and instructive but for most it is a game and far removed from reality. That is good, god forbid that most of us ever get to use our training. As Al McLuckie says "winners bleed and losers gush." Most people who find themselves using a knife will find they have lost a small peiece of themselves and wish they could regain their innocence.

Sorry to ramble,

Respectfully,

Jeff
 

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Kenpodoc said:
I'd like to add a couple of points to what I said earlier. My experiense with knife wounds is medical not as a knifer but I suspect the information is still useful.

Most peoples experience cutting tissue is either accidental or with animals post mortem. After death the tissues solidify and the feel and response to the knife is very different than pre mortem. Living tissue is harder to cut than dead tissue.

Cuts in living people are messy and that changes everything. Even superficial cuts bleed profusely and make everyone slippery. I've seen people fall in operating rooms and ERs because of the blood. Furthermore the tissue becomes difficult to stablize secondary to the slick coating of fresh blood. (older blood is sticky.)

When Living fatty tissue is cut it oozes oily liquid (think Wesson Oil.) This makes things even more slippery. The effect is far more dramatic than most people imagine.

The psycholgical issues are more complicated than Most people imagine. I've watched Law Officers and experienced Military people pass out watching operations and autopsies. Most people cause hesitation wounds the first time they try to cut even an anesthetised patient. You can train yourself to get by this but I'm not sure that it is good for people in other ways. Medical School involves a certain amount of brain washing which is essential but probably not good for the recipients. The majority of the WWII patients I've had who were frontline soldiers never fully recovered from having to kill others and deal with the death and destruction. Most remained good men but haunted by what they felt they had to do. Generally the men who talked most enthusiastically about killing were never in a position to have to do so.

I do train with knives but fear the reality. The training is fun and instructive but for most it is a game and far removed from reality. That is good, god forbid that most of us ever get to use our training. As Al McLuckie says "winners bleed and losers gush." Most people who find themselves using a knife will find they have lost a small peiece of themselves and wish they could regain their innocence.

Sorry to ramble,

Respectfully,

Jeff

:asian:

Very nice post. I've stuck pigs before and it surprised me at how long it took me to build up the courage. The prospect of killing so intimately made my stomach drop.
 

shesulsa

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Thanks, Kenpodoc. VERY good information there.
 
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Tgace

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You see them in self-inflicted stabbings. Shallow "working up the nerve" wounds before the big plunge.
 

shesulsa

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What are "hesitation wounds"?
Usually seen in suicide attempts - "first tries" before actually stabbing deeper.

edit: Dang it! Beat me to it, Tom.
 

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