Friday 12 July 2013

Forensic Friday Part 5: Stab Wounds

It's Friday! And not just any Friday: Forensic Friday! This week we're talking about stab wounds.

We're talking briefly about stab wounds because Vicki was very disorganized and didn't quite get it done the way she wanted to. Alas.

You can read all of the past episodes of Forensic Friday here

Stab wounds are pretty straight forward: a sharp object is inserted into flesh and a wound occurs. Okay that was a pretty lame explanation but stab wounds are not just for swords and assorted knives, anything sort of piercing instrument from scissors to a pencil fall into the category of “stab wound”. And like morbid, bloody butterflies, stab wounds are unique. Depending on the angle and the depth of the thrust, the width and length of the weapon, the power of the thrust, along with a number of other of factors, medical examiners can make an accurate description of the murder weapon in the absence of one. These factors include:

·         Length, width and thickness of the blade

·         Single/ double edged

·         Degree of taper from tip to hilt

·         Nature of back edge e.g. serrated or squared off

·         Face of hilt guard

·         Any grooving, serration or forking of blade

·         Sharpness of edge and extreme tip of blade

The most common stab wounds are the incised or slash wounds that are made by a sharp object makes contact with the skin, typically longer than they are deeper. A chop wound is made of blunt and sharp force injury caused by an object (usually heavy) moving at an accelerated pace. Abrasions, contusions and lacerations are common in this type of wound as well as underlying fractures.

The edges of a stab wound (on the surface) are known as the margins and the ends or tips are the angles. The length of the wound is defined by measuring the two angles and the width is defined by measuring the two margins. Depth is measured from the skin’s surface to the deepest point of penetration. If the margins are widely separated because of the elasticity of the surrounding skin, the wound is gaping. Otherwise it is called slitlike.

While a wound may be fatal, there can be very little external bleeding (in other words: ignore Hollywood) however it is most evident in cases with large, gaping wounds. It should be noted that dimensions of the wound may be inaccurate by up to 2mm due to elasticity of shrinking skin or the lengthening of an oblique entry wound.  

Regarding the angles (ends) of sharp force injuries, the angles may be sharp (coming to a point), blunt (having a squared-off appearance), or indeterminate. The directionality of the "long axis" of a sharp force wound can be described as "vertical," "horizontal," or angled, with a general or specific measurement of the angulation. One method is to describe the directionality based on a clock-face configuration. For example, "the long axis of the wound runs between the 1 and 7 o'clock positions." It should be noted that, when using this method in describing incised wounds, it is not meant to imply that the "direction" of the cutting occurred from upper (1 o'clock) to lower (7 o'clock) (see more below as well as in Common Misconceptions).

Nonlinear or irregularly shaped stab or incised wounds can result from irregularly shaped or jagged weapons, from intersecting wounds, or from a twisting weapon/body interaction. The last phenomenon can result in combined stab/incised wounds. It cannot be determined based on the configuration of these wounds whether the assailant twisted the knife while it was in the body or if the victim twisted while impaled, unless there is clear evidence that the wound occurred postmortem. - (for more on specific murder weapons. Warning: some images are graphic)

 According to Inara of Joss Whedon’s Firefly, it takes less than a pound of pressure to break the flesh and research suggests that once the skin is pierced, the knife will pass through the body with relative ease, however it depends on the sharpness of the blade.
What do you want to see for next months episode? Let me know in the comments.

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