To our best knowledge, this is the first study to validate the use of Bos taurus scapulae as a proxy for human frontal bone.
The morphometric comparison to the human samples resulted in similar measurements reported by Torimitsu et al. for overall frontal bone thickness (5–8 mm) (Torimitsu et al., 2015). Moreover, cancellous bone thickness yielded similar results with the study by Lynnerup et al. (Lynnerup et al., 2005). Their material consisted of cranial vault bone biopsies from 43 males (age range 16–90, mean ± S.D. = 48 ± 17 years) and 21 females (age range 23–84 years, mean ± S.D. = 48 ± 16 years) resulting in 2.5 mm versus the 2.0mm from our collection (Lynnerup et al., 2005). Furthermore, the averaged outer cortical layer measurements (2.4 mm) and inner cortical layer (1.8 mm) of Lillie et al. are comparable to our forensic cohort which was 1.9 mm for the outer cortical layer and 1.6 mm for the inner cortical layer (Lillie et al., 2016).
With gun violence surging worldwide, an ethical bone analog is needed for recreation of gunshot wounds to flat bone (Taylor & Kranioti, 2018; Kieser et al., 2011; Mahoney, 2018; Rickman & Smith, 2014; Smith et al., 2007). Other proxies of the human skull are used to approach various research questions and could be used to simulate impacts to the human head in court room, too, helping to recreate crimes and thus are a promising tool from a legal medicine perspective (Brickley & McKinley, 2004; Ondruschka et al., 2019). Bos taurus scapulae do seem to be an appropriate proxy to human crania for ballistic testing, which can be received from butcheries without the need of sacrificing an animal for this purpose and beyond ethical restrictions and restraints when using human donors and material. The fracture patterns during gunshot experiments obtained from these biological tissues might reflect a more lifelike pattern compared to commercially available polyurethane proxies or own 3D-printed ones based on polylactic acid (Taylor et al., 2020; Zwirner et al., 2017). However, this issue must be proved in the future in detail. Synthetic materials might not reflect the viscoelastic behavior of biological samples in an appropriate manner as they do not fracture with absolute similar patterns due to their non-viscoelastic nature and due to their manufacturing, e.g., the existence of artificial sutures between the model’s hemispheres (Taylor & Kranioti, 2018; Ondruschka et al., 2019).
With measurements of cortical bone returning comparable measurements to human frontal bones and with BMD values similar as well to human crania (Paschall & Ross, 2018), Bos taurus scapulae seem to be an appropriate proxy for ballistic recreations and also for blunt force analyses or other forensic questions, e.g., preliminary testing of a subsequently larger study cohort, given its economical use in terms of money and disposability (Taylor et al., 2020).
However, there are some limitations with Bos taurus scapulae as a proxy to human crania. Scapulae are flat bones and have no sutures (White et al., 2011) and do not encapsulate an organ with a consistency of the brain to also cover hydraulic burst effects during impact testing (Taylor & Kranioti, 2018; Kneubuehl, 2011). The effectiveness of the scapulae are limited to entrance and exit wound investigations and small radiating fractures interpretation in ballistic recreations if the appropriate areas of the scapulae are utilized with comparable thicknesses to human crania (5–8 mm) (Rickman & Smith, 2014; Smith et al., 2007; Taylor et al., 2020). Furthermore, our sample size for this study was small and our results advocate for future testing. Finally, the measurements taken for human bone samples depend on the thickness of the transversal bone cut during autopsy and are further limited to the flat part of the frontal bone.