Courtesy of Godoy Medical Forensics
Traumatic Injury Categories
Traumatic injuries can be caused by either blunt force trauma or sharp force trauma. Sharp force trauma is a broad category that covers a large group of objects that could cause these injuries. Objects such as a knife, a razor blade, a broken bottle, or even the metal lid of a can of dog food can cause sharp force injuries. Injuries that are categorized as sharp force injuries produce a wound that typically has a defined separation of the skin and the tissue.
Injuries from sharp force trauma—whether it is a knife wound or other sharp object—have specific characteristics that vary based on the motion associated with the wound. Typically, the sharp force wound from a slashing motion is longer than it is deep and does not leave any “bridging” tissue in the wound. Conversely, a wound from a stabbing motion is deeper than it is long. A sharp force object will divide and cut the skin and tissues as it penetrates. There are misconceptions in the medical arena that the terms cut and laceration are the same: this is incorrect.
A laceration is caused by blunt force trauma and is defined as “a wound that is produced by the tearing of soft body tissue. This type of wound is often irregular and jagged.” A laceration can be caused by injuries suffered in trauma, such as a motor vehicle crash or being hit by a hammer or a baseball bat. The wound is jagged in appearance with tissue that remains attached from one side of the wound to the other (see image on left).
A cut is caused by a sharp object (see image on the right). Typically, the object is forced in a specific direction along the skin and tissues, while also moving downward. What may also be seen is the wound may tail off at one end and may also be of differing depths—meaning one side may be more superficial than the other.
A knife wound can have a distinct patterns, especially if the wound is a penetrating wound or puncture. In a sharp force penetrating injury caused by a knife, what can be learned from the wound is directionality, force, blade width, and depth. Knives have a handle, and at the end of that handle is what is called the hilt. In a penetrating knife wound, if the force of the penetration is strong enough, it may cause an abrasion type wound on the skin as the hilt of the knife hits the skin.
The force may also cause a bruise to the skin. This hilt mark then provides the information on depth of the wound as the knife blade would have to penetrate the skin and tissue completely in order to create these markings.
Directionality and Blade Width
Directionality and blade width may also be determined in a penetrating knife wound. If a hilt mark is present then directionality can be determined easily, but not all penetrating knife wounds have a hilt mark. To determine directionality, the wound itself can provide that information with careful examination. Manipulating the wound by approximating (pushing together) its edges can define potential blade width and directionality. In the image to the left, the edges have been approximated to show the potential width of the blade and the direction in which it penetrated.
As seen in the image to the right, the wound appearance changes and can therefore provide an incorrect analysis of the blade.