Fragmentation characteristics of long bones resulting from impact of different ammunition sizes

Firearm violence has continued to increase, yet there remains a gap in the literature surrounding GSW fracture patterns to long bones. The majority of GSW research is centered on the cranium or thoracic bones, as they are most affiliated with fatal injuries. The present study examined differences in fragmentation and trauma characteristics on long bones caused by two ammunition types. White-tailed deer (Odocoileus virginianus) tibiae (n = 50) were encased in 10% ballistic gelatin, and 9 mm ammunition from a handgun and 5.56 mm ammunition from an assault rifle were fired from 3 yards (~2.74 m). Due to the higher potential wounding energy, it was anticipated that tibiae impacted by 5.56 mm ammunition would exhibit a greater degree of fragmentation and obscure fracture patterns. Conversely, fragmentation patterns from 9 mm ammunition were expected to be more discernible, given the lower energy transfer and smaller caliber, allowing for easier classification of fracture patterns. A Mann-Whitney U-test revealed 5.56 mm ammunition caused more fragmentation than 9 mm (p = 0.002). False butterfly fractures were observed in 48% of the 9 mm sample and 4% of the 5.56 mm sample. Chi-square tests for independence showed that all but stepped breakout (χ² [1] = 1.299, p = 0.254) had a statistical association with an ammunition type. The present study found significant differences between the frequency of observed ballistic characteristics and ammunition type within the sample; however, due to similarities, it is not recommended to use fracture pattern analysis as a method of classifying ammunition type.