A cycle rickshaw runs over legs of 10 yrs old child while playing on road. There is a tyre mark which can be seen on the child’s legs. This is (AIIMS Nov 2012)
a. Actually three choices are correct-
i. Patterned bruise
ii. Patterned abrasion
iii. Imprint abrasion. But patterned abrasion is a better answer.
b. Abrasion is of four types:
i. Scratches (Linear abrasion) - An abrasion by sharp or pointed object, not sharp enough to incise, but pointed enough to scratch eg. Fingernais, pin, thorn, tip of knife. Scratches have length but no significant width. Fingernail abrasions are straight or curved, one to two mm breadth, half to one cm long, wide at start, narrow at the end.
ii. Grazes (Sliding, scraping or grinding abrasion) - Caused by movement between skin and some rough surface in contact with it. They are commonly seen in road traffic accident. A Graze abrasion caused by violent tangential rubbing against a surface as in dragging over the ground is called brush burn or gravel rash. They are the most common type.
c. Pressure abrasion (crushing or friction abrasions) – caused by crushing of superficial layers of epidermis and are associated with bruise of surrounding area. Movement is around 90 degree to skin. In this abrasion movement is slight and directed inwards. Examples are ligature mark of hanging and strangulation.
d. Impact abrasion (contact or imprint abrasion) - Caused by impact with a rough object, when the force is applied at or near right angle to skin surface. Example when a person knocked down by a motor car, the pattern of the radiator grill, a headlamp rim or tread of tyre may be seen on the skin.
e. Impact and pressure abrasions are patterned abrasions.They reproduce the pattern of the object producing it. Patterned abrasions are produced when force is applied at right angle to surface of the skin.
f. If the skin is run over by a tyre, the ridges of the tyre damage the epidermis producing patterned abrasion, and the skin may be compressed into the alternating grooves of the tyre causing deep intradermal patterned bruise. So In case of tyre marks the ridges produce the patterned abrasion and grooves produce patterned bruise.