Abstract
Blows with axes, machetes or blunt objects such as baseball bats, truncheons, etc. are often parried, resulting in typical parry injuries, or so-called nightstick fractures to the ulna. In this study, we sought to assess the impact energy required to break the ulna in such parry incidents in an experimental setting using semisynthetic and fully synthetic models. Twenty-seven sheep radii and 33 polyurethane synthetic bones were cast into gelatin prior to being fired at with missiles made of a section of an axe blade or steel rod at different firing velocities using a compressed-nitrogen cannon. Each model was then examined as to the presence of hair-line fractures or complete fractures. Sheep bones and synthetic bones displayed comparable results when struck by the axe missile; here, a clear fracture threshold was evident between 14.00 and 15.26 J. When struck by the rod missile, only the synthetic bones produced significant results, namely a fracture threshold between 20.15 and 23.59 J. In conclusion, our results show an ulnar fracture threshold of approximately 15 J when struck by an axe. The experiments regarding blows with a rod displayed a fracture threshold of around 22 J, but, as this could not be validated with biological bones, this result is questionable.
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Acknowledgements
We are grateful to the Vetsuisse Faculty, University of Zurich and the Veterinärdienste, Umwelt-und Gesundheitsschutz Zürich for the sheep bones. Additionally, we want to thank the Medizinisch Radiologisches Institut (MRI) in Zurich for the bone densitometry and Dominic Gascho from the Institute of Forensic Medicine, University of Zurich, for CT scanning of the sheep bones. We are also indebted to Sandra Baumann, Markus Enders and Valeria Hofer from the Institute of Forensic Medicine, University of Zurich, for preparation of sheep bones and to Dr. Ronny Lorenzo of Armasuisse Science and Technology for generous permission to use the facilities and to Rudolf Bieri for assisting in the execution of the experiments.
Funding
The late Emma Louise Kessler, MD, whose legacy supported this study financially.
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Gentile, S., Kneubuehl, B.P., Barrera, V. et al. Fracture energy threshold in parry injuries due to sharp and blunt force. Int J Legal Med 133, 1429–1435 (2019). https://doi.org/10.1007/s00414-019-02022-3
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DOI: https://doi.org/10.1007/s00414-019-02022-3