Interpreting Injury Mechanisms of Blunt Force Trauma from Butterfly Fracture Formation

Abstract

According to biomechanics of fracture production during blunt impact, tubular bones are subject to compressive (impact site) and tensile (opposite impact site) forces; this causes bones to break in tension before compression, producing Y-shaped fracture patterns with breakaway (butterfly) fragments. In current forensic models, the side of the bone exhibiting the breakaway fragment is designated the impact side, with initial breakage occurring opposite. Fracture production and patterning of blunt impacts to 255 sheep femora were analyzed. Contra the existing model, only 60% of complete butterfly fractures exhibited impact side breakaway fragments. Although fractures initiated on the tension, nonimpact side, butterfly fragments formed on either compression or tension sides. Using newly defined breakaway fragment shape criteria, impact side was estimated with 98% accuracy for both complete and partial butterfly fractures. Furthermore, the results suggest that the impact site is the located on one of the Y-fracture's arms, not the butterfly fragment's center, as previously modeled.

Assessing Impact Direction in 3‐point Bending of Human Femora: Incomplete Butterfly Fractures and Fracture Surfaces,,

“…The results also highlight the limitations of relying on butterfly fracture wedge orientation to diagnose impact direction , as the present study demonstrates bending may not produce complete butterfly fractures. Because none of the specimens in the current study exhibited complete butterfly fractures, these results neither support nor contradict the results of previous investigators that complete butterfly fragments are more likely to occur on the posterior femur, regardless of impact direction. In the present study, incomplete butterfly fractures occurred exclusively as tension wedges with no fracture patterns suggestive of compression wedges.…”

“…The current results support previous experimental research demonstrating that long bone bending produces a variety of complete fracture patterns. This complicates the simple relationship between long bone bending and butterfly fractures often presented in the literature (e.g., ).…”

“…Research validating this understanding of butterfly fracture suggests that the relationship between long bone bending and butterfly fractures is more variable than typically presented in the literature . In a key engineering study, Kress reports several complete fracture types generated in bending in a large sample of human femora and tibiae.…”

“…Other experimental studies provide different reports on the expected prevalence of complete fracture types following bending failure and on the circumstances surrounding the production of compression wedge butterfly fractures . Martens et al report 4‐point bending of posterior‐loaded human femora produced only oblique or compression wedge butterfly fractures.…”

“…In the Fenton et al study, complete fracture patterns involved 60% oblique fractures, 27% transverse fractures, and 13% comminuted fractures. In 3‐point bending experiments on sheep femora, Reber and Simmons report butterfly fractures in about half the sample; of these, 60% were tension wedges and 40% were compression wedges. Even in synthetic bone, Khalil et al report variation in complete fracture patterns.…”