Fantastic plastic? Experimental evaluation of polyurethane bone substitutes as proxies for human bone in trauma simulations

doi:10.1016/j.legalmed.2015.06.007

Legal Medicine

Volume 17, Issue 5, September 2015, Pages 427-435

https://doi.org/10.1016/j.legalmed.2015.06.007 Get rights and content

Highlights

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Synthetic bones offer alternatives to animal or human remains in trauma experiments.
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We test polyurethane bone proxies in relation to three modes of ballistic trauma.
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Polyurethane spheres respond to impacts in ways that are broadly similar to bone.
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On a detailed level these proxies are less useful.
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Their uniformity makes them potentially better than real bone in trauma simulations.

Abstract

Recent years have seen steady improvements in the recognition and interpretation of violence related injuries in human skeletal remains. Such work has at times benefited from the involvement of biological anthropologists in forensic casework and has often relied upon comparison of documented examples with trauma observed in skeletal remains. In cases where no such example exists investigators must turn to experimentation. The selection of experimental samples is problematic as animal proxies may be too dissimilar to humans and human cadavers may be undesirable for a raft of reasons. The current article examines a third alternative in the form of polyurethane plates and spheres marketed as viable proxies for human bone in ballistic experiments. Through subjecting these samples to a range of impacts from both modern and archaic missile weapons it was established that such material generally responds similarly to bone on a broad, macroscopic scale but when examined in closer detail exhibits a range of dissimilarities that call for caution in extrapolating such results to real bone.

Graphical abstract

Introduction

In cases involving the analysis of skeletal remains biological anthropologists can often provide unique contributions to assist the pathologist and law enforcement agencies. One such area is in the recognition of injuries to bone where investigations of past conflict through analysis of archaeological burials have brought particular focus to injuries caused through violence. Such work generally relies on comparisons with documented injuries. In the case of more obscure or unusual mechanisms of injury, or when looking at past populations a known comparator may not be available, for example in the case of archaic weapons that are no longer in use. The best option to resolve uncertainty in such cases is through actualistic experiments.

Experimentation in controlled circumstances is attractive, but raises questions regarding suitable test samples. In simulating skeletal trauma human cadaveric samples will obviously produce results that are very close to those that would be expected in a living individual but are not necessarily the most desirable option. Human cadavers are often difficult to obtain, carry infection risks and have issues of variability between samples. Aside from these points using human remains for such work is fraught with ethical concerns and often legal complications that rule them out for many researchers. Bone from non-human animals is a promising alternative, but is complicated in respect of anatomical differences between humans and other species. With regard to some parts of the skeleton such as ribs or flat bones such as the scapula, the overall form of some mammalian bones may be sufficiently similar to humans to make these a reasonable proxy. However, the unique size and form of the human cranium remains an intractable problem as non-human crania are so different in size, shape and thickness that results obtained from them are of limited value. This point has particular relevance to trauma as the head is a common target in assaults and is also the part of the skeleton where patterns of injury are most easily recognised.

A potential alternative is presented by the commercial availability of synthetic bone substitutes formed from polyurethane. These products offer several immediate advantages over human cadavers or non-human animal bone. They can be obtained quickly in variable quantities, each specimen is identical and they avoid complications of legality, ethics and infection. It would therefore seem that such material would be an obvious choice, however, this point hinges on the extent to which these replicas respond to dynamic impacts in ways that are analogous to real bone. In a series of papers Thali et al. [1], [2], [3], [4] claimed that similar replicas produced results that were highly accurate with regard to ballistic and blunt-force trauma, although these studies concentrated largely on simulated soft tissue at bullet entrance and exit points and the general appearance of fracture patterns at a gross scale. Thali et al. [1], [2], [3], [4] focused on a small range of modern firearms and a mechanism of blunt trauma, if such samples are viable substitutes for human crania they should hold equal potential for investigations of other mechanisms of injury.

The current paper presents a pilot study designed to test this issue using a range of projectiles and mechanisms of launching them. Polyurethane bone substitute (PBS) samples were impacted with high, medium and low velocity projectiles shot using three different classes of modern and archaic weapons. The resultant defects in the samples were examined both grossly and in detail in order to assess the extent to which they resembled those produced in experimental animal bone samples and published examples of bony trauma in humans.

Section snippets

Polyurethane bone substitute (PBS)

The synthetic bone samples tested in the current study were obtained from Synbone AG (Malans, Switzerland) [5]. These products are marketed primarily as anatomical models for surgical training. The manufacturers do not give specific details about the composition of these products but describe them as being made of “specially formulated polyurethane foam” which have “in some instances the mechanical properties of natural bone” [5]. In addition to replicas of individual bones and particular

Entrance/ exit beveling -gross observations

The current project is considered a pilot study to assess the general potential of PBS as a proxy for human bone for use in larger studies. The work presented here focused on 12 PBS samples for each of the three projectile types used, with 12 cattle scapulae shot with the modern rifles included for comparison of beveled defects. The different weapon/projectile types each produced distinctive patterns of damage in the PBS test samples that were easily distinguished from each other on gross

The bigger picture

Whilst the simple bevelled defects produced by shooting both modern and obsolete forms of ammunition through flat PBS plates and empty spheres display general similarities to those seen in areas of flat bone, these lack the more complex patterns of breakage seen in real crania. However, the results of shooting PBS spheres filled with ballistic gelatin were more encouraging. On a gross level the latter are generally consistent with results obtained by Thali et al. [1], [2], [3]. The spheres shot

Conclusions

Synthetic ‘bones’ of the kind tested in this study respond to ballistic impacts in ways that are superficially similar to the forms of damage that would be expected in human cranial bone. However, important differences were noted that render this material less useful for studies conducted at a more detailed level. In spite of this criticism a case remains for using simple synthetic models of this kind in ballistic experimentation. Despite the clear dissimilarities with the way real bone behaves

Acknowledgements

Funding support for the current project was provided by Bournemouth University. We are indebted to Giles and Sandy Sturdy for kindly permitting the use of their land for the experiments described in this study and to Rob Sturdy for assisting with the preparations. We are grateful to the Assistant Chief Constable of Dorset Police for granting permission and to Sgt. John Hennessy (Firearms Training, Dorset Police, UK) for overseeing health and safety during the experiments. We also thank Dr. Luis

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Fantastic plastic? Experimental evaluation of polyurethane bone substitutes as proxies for human bone in trauma simulations

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Polyurethane bone substitute (PBS)

Entrance/ exit beveling -gross observations

The bigger picture

Conclusions

Acknowledgements

Forensic Sci. Int.

Forensic Sci. Int.

Forensic Sci. Int.

Forensic Sci. Int.

J. Archaeol. Sci.

NeuroImage

J. Mech. Behav. Biomed. Mater.

Forensic Sci. Int.

Int. J. Trauma Nurs.

Forensic Sci. Int.

Legal Medicine

J. Forensic Sci. Soc.

Forensic Sci. Int.

J. Oral Maxillofac. Surg.

Scanning Electron Microscope (SEM) analysis of gunshot defects to bone: an under-utilised source of information on ballistic trauma

J. Forensic Sci.

A case for Sherlock Holmes: forensic investigation of a gunshot wound to the head dating from Victorian London

Int. J. Osteoarchaeol.

Examination and interpretation of rifled firearm injuries

Flesh and Bone-an Introduction to Forensic Anthropology