A Numerical Model to Simulate Combat Neck Injury from Perforating Explosive Fragments
Neck injuries from explosively propelled fragments are present in 11% of injured UK soldiers and result in significant mortality and long-term morbidity. US forces in contrast only sustain neck wounds in 3-4% of those injured, which is believed to be due to their greater acceptance in the wearing of issued neck protection. A numerical simulation of the neck is desired to simulate such wounds so that potential methods of injury mitigation may be objectively compared. The aim of this research is to develop an accurate numerical simulation of neck anatomy that can provide accurate predictions of tissue damage from these fragments, which will enable objective comparisons between the potential mitigative effects of different body armour systems to be made.
Method
A high definition numerical model has been developed based on an anatomically accurate, anthropometrically representative, three-dimensional mathematical mesh of cervical neurovascular structures. An explicit Eulerian approach has been chosen, in conjunction with an LS-DYNA finite element code, to simulate the effect of a metal fragment simulating projectile (FSP) passing through cervical neurovascular structures. Currently all structures are modelled using material properties based on 20% ballistic gelatin, a tissue simulant that has been demonstrated to accurately simulate the retardation of such projectiles in tissue [2]. The predicted depth of penetration (DoP) into muscle of 20 test shots of a simulated 1.10g FSP in the simulation were compared to that produced by physical ballistic tests using a Mann-Whitney U statistical test.
Results
There was no statistical difference in the DoP for FSPs penetrating 20% gelatin compared to that predicted by the model. The model was also able to accurately represent both the temporary and permanent cavities produced by the projectile.
Conclusions
Future refinements of the model will require the incorporation of algorithms representing the material properties for each tissue type found in the neck. These will in turn require validation against animal models to confirm material properties as well as post mortem human subjects which are the only method of correctly representing the complex cervical anatomy. We believe that numerical simulation of injury to the neck could potentially enable objective comparisons of the mitigative effects of different designs of cervical ballistic protection to be undertaken prior to successful prototypes being made, with resultant time and financial savings.
References
1. Breeze J, Allanson-Bailey LS, Hunt NC, Hepper AE, Clasper JC. Mortality and morbidity from combat neck injury. J Trauma 2012; 72: 969-74.
2. Salisbury CP, Cronin DS. Mechanical Properties of Ballistic Gelatin at High Deformation Rates. Experiment Mech 2009; 49:829–840.