A direct comparison of ordnance gelatin blocks and porcine hind limbs showed significant differences in permanent cavities, temporary cavities and the infiltration depth of barium titanate particles.
In porcine hind limbs, the diameter of the bullet path and the depth of infiltration of barium titanate particles along the bullet path increased with caliber. At a penetration depth of 100 mm or more, however, we detected almost no more exogenous particles in the hind limbs.
Gunshot injuries can be examined using a wide variety of methods such as high-frequency video analysis, animal testing, and shots into human tissue simulants [16
]. Tissue simulants have different physical properties such as elasticity, the ability to regain their original shape, and density. Nevertheless, many basic systematic studies are conducted on tissue simulants in order to reduce the various influencing factors of projectiles. These studies are usually homogenously structured and provide reproducible results. The different substances that are used in these studies, however, show large differences especially in elasticity. Rutty et al. reported that the properties of gelatin blocks such as those used in our study make them an ideal model for investigations of the temporary wound cavity and possible cavitation effects [19
]. The use of multi-slice CT imaging for detecting the presence of total crack lengths has been proved to be a reliable method of investigations of terminal ballistics [20
]. Furthermore barium titanate particles in the wound allowed us to reliably analyze the contamination of wounds by exogenous particles and to determine the spatial distribution of these particles in relation to the bullet path.
Our study revealed not only significant differences between gelatin blocks and porcine hind limbs in terms of the permanent wound cavity, the temporary wound cavity and the infiltration of exogenous particles but even opposite trends in the parameters investigated. This clearly shows that the results obtained by firing projectiles and especially high-velocity projectiles into gelatin blocks can be transferred only to a limited extent to complex anatomical structures made of different tissues. The porcine hind limbs that we used in our study consisted primarily of skin with subcutaneous fat and muscle tissue. According to Jussila et al., the transferability of the results to other types of tissue is very limited [21
In our study, we used high-velocity projectiles of different calibers that do not fragment. Although the projectiles exhibited similar velocities, they caused significantly different degrees of tissue destruction and wound contamination in porcine hind limbs. The diameter of the permanent and temporary wound cavities were found to increase with caliber size. The permanent wound cavity is caused by the sound wave preceding the bullet and the displacement of tissue by the projectile. In soft tissues, however, the permanent wound cavity often collapses behind the projectile on account of the elastic behavior and displacement of tissue [22
]. High-velocity projectiles also create a temporary wound cavity in the bullet path as a result of radial tissue compression and cavity formation [9
]. The presence of gas cavities allow a temporary wound cavity to be demonstrated radiologically in spatial relation to the bullet path. Our study showed that large-caliber bullets must be assumed to create larger temporary wound cavities than small-caliber bullets. This can be explained by the larger diameter and greater weight of the projectiles, which result in the transfer of a larger amount of energy to the target.
A loss of skin integrity in association with a gunshot injury almost always leads to wound contamination by either the projectile itself or by pathogens that are present in the air or on the skin [15
]. Our results showed no direct correlation between caliber size and the depth of infiltration of exogenous particles. A greater diameter of the temporary wound cavity is associated with a larger volume of the temporary wound cavity, which increases the suction effect following the passage of the bullet. Exogenous particles, however, did not penetrate the entire bullet path or the entire temporary wound cavity. Irrespective of the caliber used, we found almost no barium titanate particles at a penetration depth of approximately 100 mm or more. The barium titanate particles that we used in our study have a size similar to that of bacteria and thus allow conclusions to be drawn on a possible contamination of the bullet path with pathogens. Accordingly, bacteria are unlikely to contaminate the entire bullet path. This confirms clinical studies conducted by Fackler et al., who also reported only mild bacterial contamination of gunshot injuries with exogenous pathogens [23
]. According to that, a series of 32 low-velocity gunshot wounds were reported by Neupert and Boyd [24
]. In our study we found the same results for the low-velocity bullets. Also in this case, there was an incorporation of particle in the gelatin. Comparing the result of our comparative experimental study, the damage resulted from projectile penetration which caused wounds characteristic of both high and low velocity penetration. We can say that the wound contamination by low-velocity in comparison high-velocity are comparable.
Gas cavities are nevertheless formed as a result of the compression of tissue in the temporary wound cavity and can be regarded as evidence of irreversible tissue compression. In summary, we must critically address the question of whether investigations in gelatin can be transferred to complex tissues in terminal ballistics.
This study provides modern treatment strategies for gunshot injuries.