Influence of rib impact on thoracic gunshot trauma

IntroductionThe influence of rib impact on thoracic gunshot trauma remains unclear, despite its high occurrence. This study therefore investigates the effect of rib impact on a bullet’s terminal properties and injury severity.MethodsTwo bullets were used: 5.56×45 mm (full charge and reduced charge) and 7.62×51 mm (full charge). For each bullet, three impact groups were tested: (1) plain 10% ballistic gelatin (control) conditioned at 4°C, (2) intercostal impact, and (3) rib impact, the latter two tested with samples of porcine thoracic walls embedded in gelatin. Analysis included penetration depth, trajectory change, yaw, fragmentation, velocity reduction, energy deposition and temporary and permanent cavity characteristics.ResultsNo significant differences were observed for most variables. Differences were found between rib (and intercostal) impact and the control groups, suggesting that the inclusion of thoracic walls produces an effect more significant than the anatomical impact site. Effects were ammunition specific. For the 7.62×51 mm round, rib impact caused an earlier onset of yaw and more superficial permanent gelatin damage compared with plain gelatin. This round also formed a larger temporary cavity on rib impact than intercostal impact. Rib (and intercostal impact) created a smaller temporary cavity than the control for the 5.56×45 mm round. For the reduced-charge 5.56×45 mm round, rib and intercostal impact produced greater velocity reduction compared with plain gelatin.ConclusionsThis study provides new insights into the role of rib impact in thoracic gunshot injuries, and indicates that the effects are ammunition dependent. Unlike the 5.56×45 mm rounds, rib impact with the 7.62×51 mm rounds increases the risk of severe wounding.

Distribution of Bacteria in Simplified Surrogate Extremities Shot With Small Caliber Projectiles

Experiments were conducted to determine bacteria distribution trends in wound cavities of simplified surrogate extremities shot using small caliber projectiles. Two different shapes of targets, cylindrical and square, were used in this study. Cylindrical targets are more representative of an extremity but create difficulties while conducting tests due to inconsistent cavity lengths and optical distortions. Square targets, which are not as susceptible to the problems mentioned above, could be used in place of cylindrical ones if their shape does not significantly affect the distribution of bacteria within the wound cavity. Surface contamination of the targets in the experiments was represented using a circular piece of filter paper moistened with a solution with a known amount of Escherichia coli strain K-12. The projectiles used were 11.43-mm (0.45-in) caliber round nose projectiles shot from a commercially available air rifle. The permanent cavities were extracted from the targets and sliced into small, evenly spaced segments and the area surrounding the permanent cavities was removed with a biopsy punch. The radial tears that were made by the formation of the temporary cavity and surround the permanent cavity were removed using a scalpel. The permanent cavity and radial tears for each section were processed and plated on agar plates. Commercial software was used to count the number of colony forming units on each plate and the percentage of the total bacterial colony count per segment was determined. High speed video and motion analysis software was used to qualitatively and quantitatively compare the temporary cavities in the cylindrical and square targets. The data from the experiments showed that the bacteria distribution trends for the cylindrical and square targets were similar even though the maximum openings of the temporary cavity at the entrance and exit locations were higher for the cylindrical ones. For both target shapes, the bacterium was evenly distributed between the permanent cavity and the radial tears in the middle sections of the “wound tracks.” In addition, significantly higher amounts of bacterium were found in the entrance and exit segments compared with the rest of the segments in the “wound tracks”.

Stress Wave in Gelatin from Temporary Cavity

To study the injury mechanism of stress wave from temporary cavity in gelatin, a stress wave propagation model is established. Based on experimental phenomena, gelatin around the trajectory is divided into fail region and elastic region. In the fail region, gelatin is considered to be incompressible and loop stress is zero. Gelatin in the elastic region is assumed to be plane-strain. Moving equations in the two regions are built. A 4.8 mm steel sphere is fired into gelatin at 720 m/s. Displacements of the temporary cavity are obtained from the experiment. By solving the moving equations with boundary conditions, amplitude of cavity pressure, radial stress distribution in gelatin are obtained. The theoretical results can be used to explain stress waves produced by temporary cavity.

Factors affecting temporary cavity generation during gunshot wound formation in animals – new aspects in the light of flow mechanics: a review

There is controversy regarding the causes of temporary cavity generation during gunshot wound formation. Analysis of gunshot wounds in hunted animals suggests that a bullet’s frontal surface shape is the primary factor in forming a temporary pulsating cavity, and that cavity size is not directly affected by bullet velocity.