CHAPTER 1 Trace evidence from the impacting surface may be ...

1 Lecture Notes in Forensic Medicine Derrick Pounder, University of Dundee-1- CHAPTER 1 BLUNT FORCE INJURIESA wound is a disruption of the continuity of tissues producedby external mechanical force. The term injury is usedsynonymously with wound, but can have a wider meaning andencompass not only damage produced by physical force, butalso damage produced by heat, cold, chemicals, electricity andradiation. The English word injury derives from the Latinword injuria which literally means not lawful.

2 The termlesion originally meant an injury but has now come to be morewidely applied to include any area of injury, disease, or localdegeneration in a tissue causing a change in its function orstructure. Therefore use of the terms injury or wound implydamage from unnatural causes, while the use of the termlesion is non-committal on whether the cause of the damagewas natural disease or , or injuries, are generally classified according to theircause as blunt force injuries, sharp force injuries, gunshotinjuries, and a miscellany of others, including for exampleburns.

3 This is the classification followed in this text, and eachgroup of injuries is discussed in successive blunt force injury is any bodily damage resulting fromforceful contact between the body and a blunt object. Theforceful contact most commonly involves movement andimpact, with the resulting transfer of kinetic energy. Either themoving object strikes the body as in a blow, or the movingbody strikes an unyielding object as in a fall. Less often thephysical force is applied more slowly by the pressure ofcrushing, squeezing, or pinching.

4 Crushing or scraping of theskin produces abrasions(grazes).Bruises occur when theelastic limit, the tolerance, of subcutaneous blood vessels isexceeded so that they tear and forces areneeded to tear the skin to produce lacerations. These threeblunt force injuries abrasions, bruises, and lacerations mayoccur singly or together in any abrasion is an area of crushing or loss of skin,or mucousmembrane,resulting from contact with a blunt are typically superficial, trivial injuries which maybe overlooked easily but provide useful forensic bleed only slightly.

5 Heal quickly and leave no between an object and the skin causes atypical graze in which the superficial skin layers are scrapedoff and piled up as skin tags at the far end of the injury. Thelocation of the skin tags indicates the relative direction ofmovement between the object and the patches of abrasion are sometimes described as brushabrasions, the frictional element of which gave rise to the term brush burns , as in for example carpet burns . They are seenin their most florid form as road rash ,following a motorvehicle collision in which the victim, typically a motorcyclist,slides along the road evidence from the impacting surface may be presentwithinagraze and can be recovered for identification andmatching with the impacting object, for example paint from avehicle in a hit and run death of a.

6 Fragments of skin transferred to the impacting object may bematched to the victim using serology or DNA of a graze for the presence of skin tags and traceevidence is easier using a hand-held magnifying scratch is a linear abrasion produced by drawing a sharppoint over the surface of the skin or mucous membrane. Plantthorns and barbed wire are common causes of of skin tagsat one endindicates the direction of fingernails and animal claws are otherimportant causes of scratch spacing andconvergence of several scratch marks may allow a distinctionbetween human and animal and between adult and quantities of skin can be recovered from beneathfingernails which have been used for scratching.

7 And linked tothe person who was scratched by serology or DNA from beneath the fingernails is recovered by clippingthe nails with clean scissors, scraping beneath the nails usingwooden orange sticks , or cleaning beneath the nails usingpointed cotton tangential impact between an object and the skin willproduce a graze or scratch, direct impact at approximatelyright angles (90 ) to the skin surface will produce a crushabrasion, which imprints the pattern of the causative objectupon the skin surface .

8 These imprint or patterned abrasionsmay result from forceful impact, asin a pedestrian struck by avehicle, or alternatively may result from a more slowly appliedcrushing force, such as in strangulation by of patterned abrasions lies in the fact that theirshape can be matched to the causative object, and for thisreason they should be documented by photography with ascale, or by an accurate tracing. Common examples of imprintabrasions are the sole patterns of footwear in kicking assaults,and motor vehicle tyre tread marks in run-over pedestriandeaths.

9 In deaths from hanging the ligature typically leaves adistinct imprint abrasion which is accentuated by thecontinued suspension of the body after death. Fingernails, aswell as producing scratch abrasions, can produce semi-lunarand linear imprint abrasions. The hilt of a knife may leave animprint abrasion adjacent to a stab wound, suggesting theforceful penetration of the entire length of the abrasion across the chest of a motor vehicle collisionvictim suggests that a three-point seatbelt was being worn atthe time of the most superficial abrasions there is crushing and loss ofonly the epidermis so that there is no bleeding andoftennoinflammatory reaction.

10 Slightly deeper abrasions involve thesuperficial dermis, appear red-based, may bleed slightly, andproduce an exudate which dries within a day to form a yellow-brown scab. Abrasions produced after death, or immediatelyprior to death, have a dried red, orange or yellow base and aredescribed as parchmented abrasions because they the post-mortem interval increases theseparchmented abrasions dry out and harden further, becoming aLecture Notes in Forensic Medicine Derrick Pounder, University of Dundee-2-dark brown or black colour.