According to the Federal Bureau of Investigation’s Uniform Crime Reports, the total number of murders in 2016 in the United States was 15,070. Of those murders, knife wounds and other cutting objects were the third leading cause, accounting for 1,604 deaths. The states with the largest number of knife/cutting instrument deaths in 2016 were California, with 280, and Texas, with 175 (The Federal Bureau of Investigation, 2017).
Two Types of Traumatic Injury
In the world of forensics, traumatic injuries can be caused by either blunt force trauma or sharp force trauma. Sharp force trauma is a broad category including a large group of potential objects that cause these injuries. Knives, razor blades, broken bottles or even lids from metal cans can cause sharp force injuries. The result is a wound that typically has a defined separation of the skin and the underlying tissue.
Sharp force trauma injuries have specific characteristics. Typically, the sharp force wound is longer than it is deep, and does not leave any “bridging” tissue in the wound. A sharp force object will divide and cut the skin and tissues as it penetrates.
There is a misconception in the medical arena that the terms cut and laceration are interchangeable; this is incorrect. A laceration is defined as, “… a wound that is produced by the tearing of soft body tissue. This type of wound is often irregular and jagged” (Heller, 2015). A laceration can be caused by injuries suffered in traumas 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 1).
A cut, on the other hand, is caused by a sharp object (See image 2). Typically, the object is forced in a specific direction along the skin and tissues, while also moving downward. The wound may tail off at one end, and it may be of differing depths; additionally, one side of the cut may be more superficial than the other (Lynch, 2006). The bottom line: Lacerations don’t usually indicate knife wounds, while cuts often do.
A knife wound can have a distinct pattern, particularly when the wound is a penetrating wound or a puncture. When a knife causes a sharp force penetrating injury, the resulting wound provides evidence of directionality, force, blade width and depth. A knife has a handle with a hilt where the handle attaches to the blade (see blue arrow above). If the force is strong enough in a penetrating knife wound, the hilt may cause an abrasion type wound where it hits the skin (See image 3). That force may also cause a bruise to the skin as seen in image 4. This hilt mark indicates the depth of the wound, as the knife blade must completely penetrate the skin and underlying tissue to create these markings (See images 3 and 4).
If a hilt mark is present, then directionality is determined, but some penetrating knife wounds leave no hilt mark. In this case, careful examination of the wound itself can reveal directionality. Manipulating the wound by approximating (pushing together) its edges can define both potential blade width and directionality. In image 5, the edges have been approximated to show the potential width of the blade and the direction in which it penetrated. As seen in image 6, the wound appears smaller before approximation, and initially offers little information about the blade, but expert examination of the wound yields a more accurate assessment.