CHAPTER 1 Trace evidence from the impacting …

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. 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.

2 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. 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, 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.

3 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 ,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.

4 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, 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.

5 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. 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.

6 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. Superficial abrasions on a wet ordampcorpsemay escape notice until they dry out and , abrasions provide useful forensic information becausetheir location reflects precisely the point of impact with thecausative object, grazes indicate direction, imprint abrasionsreflect the shape of the causative object, Trace evidence fromthe object may be found in the graze, and skin fragments fromthe victim may be recovered from the causative bruise is a haemorrhage into tissues.

7 Synonyms arecontusion and ecchymosis (plural: ecchymoses).Very smallbruises, ranging in size from a pinpoint to a pinhead, may bedescribed as petechiae, or petechial haemorrhages, oralternatively as punctate haemorrhages. Haemorrhage orbleeding is the process which produces a bruise in tissues, butthe term haemorrhage also encompasses bleeding which maynot be associated with bruising, a bleeding nose, or ableeding stomach tissue may bruise, but bruises confined to deeper tissues,such as skeletal muscle, are not visible on the skin the deep tissues, even when fatal, may not beevidenced by any injury to the skin surface. For example, afatal head injury,such as asub-dural haemotoma, may beencountered without recognisable superficial bruising; fatalstrangulation with extensivebruising of the muscles of theneck may be accomplished without obvious bruising of theskin; and blows to the abdomen, although producingbruisingandruptures of internal organs, may not produce anyabdominal wall bruising of the skinand subcutaneous tissues, and themucosa of the mouth, vagina and anus, is visible at a clinicalexamination.

8 A simple bruise is a discolouration resultingfrom haemorrhage beneath the skin or mucosa, without anyassociated breach in the surface. The blood vessels rupturedare typically the capillaries and small veins rather and mucosal bruises may be accompanied byabrasions and lacerations, but they are notusuallyassociatedwith cuts and stabs, where there is a free flow of blood fromthe cut vessels rather than infiltration of blood into the are accompanied by swelling from the haemorrhageitself and the resulting inflammation. If the extravasated bloodcollects as a discreet tumour-like pool, the lesion is referred toas a haematoma. Bruisesare usually painful and tender topalpation as a result of damage to local nerve endings and theinflammation. Focal necrosis of subcutaneous fat may occur atthe site of a bruise, and a secondary aseptic inflammation inresponse to the irritant effect of fat liberated from the rupturedcells produces a hard chronic lesion.

9 This is more of clinicalthan forensic importance since a common site is the breastwhere it may be mistaken for a carcinoma. Bruises of the skinif numerousand large enough can be life-threatening as aresult of blood lossbut this isan uncommon are produced typically by a blunt force impact, such asa blow or a fall, butcanresult also from crushing, squeezingor ,with or without abrasion, to the bonyprominences of the back ( the shoulder blades, sacrum andpelvis)may be caused byforce applied to the front of a supinebody with resultant counter-pressure between an underlyingfirmsurfaceand the back,as inforceful restraint on thegroundduringa rape, or a stamping assault. Similar counter-pressurebruising may be seen on the bony prominences ofthe front of the pelvis (the anterior superior iliac crests) inattempted anal called love-bites ( hickeys inAmerican slang) are superficial bruises produced by thenegative pressure of mouth suction.

10 They are commonly foundon the side of the neck and occasionally the breast and innerthigh. Theyare sometimesself-inflicted on accessible parts ofthe arms to simulate evidence of an assault. Natural diseases inwhich there is an abnormality of the clotting mechanism of theblood, such as leukaemia,scurvy (vitamin C deficiency),andliver disease,causeso-called spontaneous bruising which isthought to result from unrecalled trivial trauma. Floridspontaneous bruising (purpura) may be seen in children withfulminating meningococcal size of a bruise is an unreliable indicator of the degree offorce which caused it, because several other factors, such asanatomical site, gender, age and the presence of naturaldisease, all influence bruise occurs morereadily where there is a lot of subcutaneous fat, such as on thebuttocks and thighs, and therefore more readily in the obese, inwomen and in occurs readily in loosetissues, such as around the eyes and genitals, and less readilywhere the skin is strongly supported by fibrous tissue, such asthe palms, soles and scalp.