MORPHOLOGYAnabrasion isawoundproducedbyscrapingorrubbingtheskinsurface,whichdamagesthesuperficiallayer.Typicalskinabrasionsremoveonlytheepidermallayer.Acontusion, orbruise,isawoundusuallyproducedbyablunttraumaandischaracterizedbydamagetoavesselandextravasationofbloodintotissues.Alaceration isatearordisruptivestretchingoftissuecausedbytheapplicationofforcebyabluntobject.Incontrastwithanincision,mostlacerationshaveintactbridgingbloodvesselsandjagged,irregularedges.Anincised wound isoneinflictedbyasharpinstrument.Thebridgingbloodvesselsaresevered.Apuncture wound istypicallycausedbyalong,narrowinstrumentandistermedpenetrating whentheinstrumentpiercesthetissueandperforating whenittraversesatissuetoalsocreateanexitwound.Gunshotwoundsarespecialformsofpuncturewoundsthatdemonstratedistinctivefeaturesimportanttotheforensicpathologist.Forexample,awoundfromabulletfiredatcloserangeleavespowderburns,whereasonefiredfrommorethan4or5feetawaydoesnot.
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Fig. 8.13 (A)Lacerationofthescalp:Thebridgingstrandsoffibroustissuesareevident.(B)Contusionresultingfromblunttrauma.Theskinisintact,buthemorrhageofsubcutaneousvesselshasproducedextensivediscoloration.(A and B, From the teaching collection of the Department of Pathology, University of Texas Southwestern Medical School, Dallas,Texas.)
Oneofthemostcommoncausesofmechanicalinjuryisvehicular accident. Injuriestypicallysustainedresultfrom hittingapartoftheinteriorofthevehicleorbeinghitbyobjectsthatenterthepassengercompartmentduringthecrash,suchasengineparts;(2)beingthrownfromthevehicle;or beingtrappedinaburningvehicle.Thepatternofinjuryrelatestowhetheroneorallthreeofthesemechanismsareoperative.Forexample,inahead-oncollision,acommonpatternofinjurysustainedbyadriverwhoisnotwearingaseatbeltincludestraumatothehead(windshieldimpact),chest(steeringcolumnimpact),andknees(dashboardimpact).Commonchestinjuriesstemmingfromsuchaccidentsincludesternalandribfractures,heartcontusions,aorticlacerations,and(lesscommonly)lacerationsofthespleenandliver.Thus,incaringforanautomobileinjuryvictim,itisessentialtorecognizethatinternalwoundsoftenaccompanysuperficialabrasions,contusions,andlacerations.Indeed,inmanycases,externalevidenceofseriousinternaldamageiscompletelyabsent.
Both excess heat and excess cold are important causes of injury. Burns are all too common and are discussed first; a brief discussion of hyperthermia and hypothermia follows.
In the United States, burns cause 3500 deaths per year and result in the hospitalization of more than 10 times that many persons. Many victims are children, in whom the cause of injury often is scalding by hot liquids. Fortunately, since the 1970s marked decreases have been seen in both mortality rates and the length of hospitalizations. These improvements have been achieved through better understanding of the systemic effects of massive burns and the discovery of better ways to prevent wound infection and to facilitate the healing of skin surfaces.
The clinical severity of burns depends on the following important variables:
Percentage of body surface involved
Whether internal injuries from the inhalation of hot and toxic fumes are present
Promptness and efficacy of therapy, especially fluid and electrolyte management and prevention or control of wound infections