Analysis of experimental cranial skin wounding from screwdriver trauma

Abstract

As part of a more extensive investigation of skin wounding mechanisms, we studied wounds created by five common screwdrivers (straight, star, square or Robertson, Posidriv and Phillips) on the shaven foreheads of 12 freshly slaughtered pigs. We fixed the different screwdriver heads to a 5-kg metal cylinder which was directed vertically onto each pig head by a droptube of 700 mm length. We examined skin lesions by photography and also by scanning electron microscopy (SEM). Our evaluation of differences in wound shape and size was based on geometric morphometric methods. Our results show that there are obvious morphological differences between the straight head and the other types. The straight-headed screwdriver penetrates the skin by a mode II crack which results in a compressed skin plug with bundles of collagen fibres forming skin tabs within the actual wound. The sharper-tipped screwdrivers wedge open the skin (mode I), with a clearly defined edge with no skin plugs. Geometric morphometric analysis indicates that shapes of skin wounds created by the five screwdriver types could be classified into three different groups. The straight head results in the most differentiated wound profile, with the Robertson or square and some specimens of star, and also the Posidriv and Phillips giving similar wound outlines. SEM evaluation of wounds created by a new and worn straight-head screwdrivers shows that the outline of the worn screwdriver head is reflected in the shape of the wound it created.

Differentiation of serrated and non-serrated blades from stab marks in bone

“…In practice, this will affect the ability to distinguish the subtle differences between non-serrated and serrated blades. The surface of a blade can also result in striations on the kerf wall that can be related to saw or knife class [14,24] although one would also expect this to be affected by the ratio of cancellous to compact bone at the cutmark site.…”

“…As such, this technique is non-destructive and arguably more precise than traditional methods. Furthermore, it has been used in previous research of this nature [14].…”

“…Previous work has focussed on interpreting sharp-force trauma from bone in order to make statements about the context of death in both forensic and archaeological contexts. Such work includes the definition of kerf dimensions and properties [9,10], the differentiation of cutmark origin [9,10,11,12,13,14], the impact of other taphonomic processes on cutmark preservation [15,16], patterns of butchery and dismemberment [10,17,18,19] and describing the details of the trauma incident itself [1,2,4,5,6,7,20,21]. Although research has demonstrated that it is possible to distinguish the class of sharp object used from the mark left behind, it is difficult to be any more precise than that.…”

“…In addition, casts have been attempted on soft tissue cutmarks with some success [22]. Some work has examined the force necessary to penetrate the soft tissues [1,3], but other than the work of Kieser et al [14], no attempt has been made to determine the relationship between cut marks in soft tissue and the underlying hard tissue.…”

Quantification of forces required for stabbing with screwdrivers and other blunter instruments

“…Their findings showed that there was a direct correlation between the penetration mechanism and the geometry of the punch tip [20]. Kieser et al showed that a sharp tip punch penetrated via a mode I crack whereas a blunt tip exhibited a mode II crack [21,22].…”