Abstract
Sharp force trauma is routinely encountered in forensic practice. Often the question is posed, how much pressure or energy would have been necessary to inflict a cut with a specific knife, in order to further characterize the perpetrator or determine his intent to cause harm. This paper investigates two knife blades and its individual pressures needed to cut through the epidermis and dermis. In order to examine the necessary force for cutting through the skin, we performed experiments on a piglet skin-on-gelatin phantom. Two similarly small knives—a paring knife with a serrated blade and a Swiss Army pocket knife with a smooth blade—were moved over the phantom surface using a mobile cutting apparatus with varying weight on the load arm with the knife. The depth of the cut was to be determined according to a scale from zero to three: grade 0 = no cut; grade 1 = cut into epidermis only; grade 2 = cut into dermis; grade 3 = complete transection of the entire skin. Each cut inflicted at a specific pressure force was assessed closely in order to ascertain depth, calculate the velocity, and ultimately determine the point at which a cut would inflict grade 3 damage. The smooth blade of a pocket knife needed at least 1900g pressure in order to slice through pig skin mounted on a thick gelatin block, whereas a serrated blade of a paring knife managed to cut into or through the dermis at a comparatively lower force of 700g. Our study shows that at the same cutting velocity, a significant difference in pressure is necessary to inflict the same degree of damage.
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Acknowledgments
The authors would like to thank the late Emma Louise Kessler, MD, whose legacy supported this study financially. We are grateful to Markus Enders from the Institute of Forensic Medicine, University of Zurich, for preparation of the gelatin and assisting in the experiments; to Valeria Hofer helping with the experiments; to Cedric Bolliger for assistance in designing and constructing the cart; and to Kevin Wallace for manuscript editing.
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Bolliger, S.A., Wallace, E., Dobay, A. et al. The cutting edge—an investigation into the pressure necessary for cutting skin with different knife blade types. Int J Legal Med 134, 1133–1140 (2020). https://doi.org/10.1007/s00414-020-02270-8
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DOI: https://doi.org/10.1007/s00414-020-02270-8