Abrasion and their Forensic Significance

An abrasion is a common type of injury that occurs when the skin gets grazed or torn off. It is destruction of the skin which usually involves the superficial layers of the epidermis only. They are caused by a blow, a fall on a rough surface, by being dragged in a vehicular accident, finger-nails, thorns or teeth bite. Some movement and pressure by the agent on the surface of the skin is essential. The size varies depending on the extent of the body surface exposed to the abrading force. When they heal there is no permanent scar. This is the tyoe of Mechanical injury due to blut force. Also known as “Gravel Rash.”

Types of Abrasions

• Scratches: A scratch (linear abrasion) is an abrasion with length but no significant width, or a very superficial incision, they are caused by a sharp object passing across the skin, such as, finger-nails, pin or thorn.
• Grazes (sliding, scraping or grinding abrasions): They are the most common type. They occur when there is movement between the skin and some rough surface in contact with it. They show uneven, longitudinal parallel lines (grooves or furrows) with the epithelium heaped up at the ends of these lines, which indicate the direction in which the force was applied.
• Pressure abrasions (crushing or friction abrasions) – They are caused by crushing of the superficial layers of the epidermis and are associated with a bruise of the surrounding area. If the movement of instrument is around 900 to the skin, a pressure type of abrasion occurs. In this type, the movement is slight and largely directed inwards. The ligature mark in cases of hanging and strangulation and the teeth bite marks are the examples.
• Impact abrasions (contact or imprint abrasions) – They are caused by impact with a rough object, when the force is applied at or near a right angle to the skin surface. The abrasion is slightly depressed below the surface, unless there is bulging due to underlying contusion or local oedema. If the impact is forcible, the dermis is damaged with an underlying bruise.

Difference Between Antemortem and Postmortem Abrasions.

Characteristics and Forensic Significance of Abrasion. 

On drying, abrasions become dark brown or even black. When it is Fresh they are Bright red. On 12 to 24 hours Lymph and blood dries up producing bright red scab. Following 2 to 3 days they go to Reddish brown scab.  On 4 to 7 days Epithelium covers the defect under the scab and after 7 days Scab dries, shrinks and falls off.

Abrasions are usually seen in accidents and assaults. Suicidal abrasions are rare. There are some Artefacts in Abrasions and they can be differentiated from:

• Erosion of skin produced by ants.
• Excoriations of the skin by excreta.
• Pressure sores.

Forensic Significance

• They Indicates site of impact and direction of the force.
• They may be the only external signs of a serious internal injury.
• Patterned abrasions are helpful in connecting the crime with the object which produced them.
• The age of the injury can be known.
• In open wounds dirt, dust, grease or grit are usually present, which may connect the injuries to the scene of crime.

Manner of injury may be known from its distribution: In throttling, curved abrasions due to finger-nails are found on the neck. In smothering, abrasions may be seen around the mouth and nose. In sexual assaults, abrasions may be found on the breasts, genitals, inside of the thighs and around the anus. Abrasions on the face or body of the assailant indicate a struggle.