Appearance of Stab Wounds in Skin

The size and shape of a stab wound in the skin depends on the nature of the blade and knife, the direction of the thrust, the movement of the blade in the wound, the movement of the individual stabbed, and the state of relaxation or tension of the skin. The sharpness of a weapon will determine the appearance of the margins of the wound: sharp and regular; abraded and bruised, or jagged and contused. With a blunt cutting edge, the edges of the wound may be abraded. If an individual is stabbed such that the flat surface of the knife blade is at an oblique angle to the skin, the stab wound will have a beveled margin on one side with undermining on the other, indicating the direction from which the knife entered.

The parts of a single-edge knife (Figure 7.2) are:

The appearance of a stab wound can be influenced by how deep the knife is thrust in and what portion of the shaft penetrates or contacts the skin. If

Knife Wound Direction
Figure 7.2 Parts of single-edge knife.

the knife is thrust with great force into the body up to the guard, then the imprint of the guard could be on the skin. If the knife is thrust in up to the ricasso, the wound can be squared at both ends.

The shape of a stab wound in the skin is determined not only by the shape of the blade, but by the properties of the skin. If a stab wound is inflicted when the skin is stretched, the resulting long, thin wound will assume a shorter, broader appearance when the skin relaxes. Langer's lines can also influence the appearance of a wound. Langer's lines are a pattern of elastic fibers in the dermis of the skin, which is approximately the same from individual to individual. Plastic surgeons take advantage of this pattern of fibers to conceal scars. If one is stabbed across these lines, that is, perpendicular to the fibers, the fibers will pull apart the edges of the wound, creating a gaping wound (Figure 7.3). Stab wounds parallel to Langer's lines produce narrow slit-like wounds. Between the two extremes are oblique wounds. Here, depending on the pattern of the fibers, the wounds may be asymmetrical or semicircular. If the edges of a gaping wound are drawn together, the size of the restored wound approximates the maximum possible width of the knife blade.

If a double-edged weapon is used to stab an individual, the wound produced will show bilateral pointed ends. If a single-edged weapon is used, theoretically, one end of the stab wound is pointed and the other is squared off or blunted (Figure 7.1). However, stab wounds with double-edged weapons are uncommon in the U.S. Virtually all stab wounds seen are made with single-edged weapons. When actual wounds are examined, it becomes obvious that a number of stab wounds caused by single-edged weapons have bilateral pointed ends like those made with double-edged weapons. There are two explanations for this. First, as the tip of the knife perforates the skin,

Knife Stab Simulations

Figure 7.3 (A) Multiple stab wounds with same knife. Varied shapes to wounds due to Langer's lines. Effect of Langer's lines on stab wound perpendicular to (B) and parallel to (C) lines.

Figure 7.3 (A) Multiple stab wounds with same knife. Varied shapes to wounds due to Langer's lines. Effect of Langer's lines on stab wound perpendicular to (B) and parallel to (C) lines.

it is pulled down, with the cutting edge slicing through the skin and the squared-off back of the knife not imparting its configuration to the skin because it does not contact it. Second, many single-edged knives have a cutting edge on the back of the knife at the tip. Thus, the initial plunge into the skin will produce a double-pointed wound. Then, as the rest of the knife goes through the skin, if it is pulled down slightly, the back or squared off portion of the knife will never contact the skin.

Thus, while in theory one can look at a stab wound and say the weapon was single- or double-edged, in reality, it is not always possible through examination of a single wound. If an individual is stabbed multiple times with a single-edged knife, examination of the wounds will eventually disclose the typical single-edged configuration.

As a knife is withdrawn from the body, it may be twisted or the person stabbed may move. In such a case, the knife might produce a Y- or L-shaped wound (Figure 7.4). There will be a primary stab wound with an extension caused by the knife's edge cutting a secondary path as it exits. A variation of this can be seen when the knife is only slightly rotated or the individual moves only slightly, such that one end (the cutting end) of the stab wound will have an inverted V-shaped notch or "fork" in it (Figure 7.5)Thus, in this situation with a single-edged knife, one end of the stab wound will be squared or blunted and the other will be forked.

This picture of a fork at one end of a stab wound caused by the cutting edge of the knife can be simulated by tears in the skin at the squared-off end of the stab wound produced by the back of the blade (the ricasso) lacerating the skin as the blade is plunged in. These tears can usually be differentiated from the fork cuts in that they are not as sharp and clean and are often confined to the superficial layers of the skin (Figure 7.6).

The most common reason for a large, irregular knife wound is movement of the victim as the weapon is withdrawn. Prosecutors, however, often contend that this is due to the perpetrator's twisting the knife in the body after stabbing the individual.

If a knife is plunged into the body with such great force that the full length of the blade enters, a patterned abrasion around the stab wound can be caused by the guard (Figure 7.7), which is a metal piece between the blade and handle originally designed to keep the user's hand on the handle. Use of the term "hilt" is technically incorrect, because that term refers to swords. A mark from a guard will be symmetrical if the knife is plunged straight in. (Figure 7.7A) If the knife is plunged in a downward angle, then the guard mark will be prominent above the stab wound; if the knife is plunged upward, the guard mark will be below the stab wound. In oblique stab wounds, a knife plunged in from the right will have a guard mark on the right (Figure 7.7 (B, D)).

In some stab wounds, examination of the wound will reveal both ends to have a squared-off or blunt appearance. This is caused by the knife's being plunged in the full length up to the guard. In most weapons, between the true edge of the knife and the guard, there is a short, unsharpened section of blade called the ricasso. This generally has a squared-off configuration that is identical on both the back and the cutting edge of the knife. Thus, if the knife goes in all the way, one end of the stab wound will be squared off by the back of the knife, and the other by the ricasso.

Ricasso WoundsLines Langers Stab WoundsKnife Stab Wounds
Figure 7.4 (A, B and C) Irregular configuration of stab wounds caused by knife's being twisted or movement of victim as blade is withdrawn.
Photos Knife Wound Victims

Figure 7.5 (A) Stab wounds from a single-edge knife with small forks at the cutting-edge end caused by the knife's being withdrawn. (B) Double-edged stab wound with fork at one end.

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