Sharp and Cutting Instrument Wounds: Characteristics and Mechanisms
Wounds by Sharp Instruments
These wounds are produced by instruments of elongated shape, with a diameter that is variable but never very large, and a circular or elliptical section, which ends in a more or less acute point. Therefore, they are elongated cylindrical bodies with a sharpened tip. They can be natural or artificial. Natural examples include spines, stingers, and other animal defenses. Artificial examples include pins, needles, punches, arrows, rapiers, and spears.
Mechanism of Action
They penetrate the tissues acting as a wedge, a living force that focuses on the tip, laterally displacing the fibers of the traversed tissues.
Characteristics of the Lesions
They are defined by an orifice and completely cross the affected area. The inlet hole is normally on the skin, rarely on the mucosa. There is an imbalance between the dimensions of the external wound and the instrument. There are two types of injuries:
- Punctate: The damaging instrument is fine, leaving a reddish point whose impact disappears in 2-3 days.
- Eyelet: The instrument is thicker, leaving a wound in the form of a slit with slightly rounded, clear, and equal angles (like an eyelet).
The shape and direction of the inlet are important in forensic medicine.
Filos’ Law (1833)
- An injury caused by a cylindroconical weapon simulates a weapon with two edges.
- In a given region, the lesions produced by this type of weapon always have the same direction, while those resulting from a needlestick weapon with two edges may have the most diverse directions.
Langer’s Law (1881): When a sharp instrument infringes a point at which different systems of fibers with divergent directions converge, the wound takes a triangular or arrow shape.
The trajectory of sharp injuries consists of a canal that runs through the various tissues. A characteristic lesion is that the direction of the eyelet is different in each case.
The outlet is usually more irregular than the inlet, with atypical fissures and cracks. Its size is generally smaller than the inlet.
Prognosis
It depends on the following factors: the thickness of the instrument, the wound area, the depth of the injury, the cleanliness of the instrument, etc.
Wounds by Cutting Instruments
These are defined by the existence of a thin sheet and a triangular section with an edge. True cutting instruments are represented by knives, razors, scalpels, etc.
Mechanism of Action
The edge penetrates the tissue, producing a wedge and splitting the continuity of the tissue.
Characteristics of the Lesions
There are three types: linear wounds, flap wounds, and glancing wounds.
Linear Wounds
The instrument enters perpendicular to the skin, producing a simple solution of continuity. The open wound is an elongated oval, extending superficially. The distinguishing features of these injuries are:
- Borders: Incised wounds are characterized by the regularity and cleanliness of their edges. When they retract, they give the wound a fusiform shape.
- Ends: They often end up becoming superficial, forming what are called tails. There is a more apparent attack tail at the start of the cut and a terminal tail.
- Walls: The depth results in the formation of two walls that are smooth and regular, and there are never any substance bridges linking the walls.
Flap Wounds
These occur when the sharp instrument penetrates more or less obliquely, so that one edge is obtuse with a beveled cut, while the other is a foil or flap of triangular section with a thin free edge. The size and thickness can vary depending on the length of the weapon, the obliquity of the cut, and its depth.