Mechanical or thermal damage: differentiating between underlying mechanisms as a cause of bone fractures.

To investigate the differences between pre- and post-fire fractures, 30 human forearm bones were subjected to either blunt-force impact, burning, or both. Bones, covered in soft tissue and wrapped in clothing, were burned in a reconstructed house fire. The burning context and dynamics led to differential burning, that was equal amongst the three groups. To evaluate the damage to the bones, a data collection sheet was developed based on the current literature on fracture features. To analyze the relation between exposure temperature and fracture class and occurrence, color was measured to estimate the exposure temperature. Observable and measurable changes on bone, and fracture surfaces, were macro- and microscopically analyzed. Many features overlapped between the three groups, and thus are not usable for differentiation. Fractures caused by blunt force impact (post-mortem, pre-fire) showed a rough fracture surface with smoothness in curved/slanted regions near the margin after burning, while heat-induced bone fractures showed a smooth fracture surface. The margins and surface of bone fractures that originated after the fire (indirect heat-induced) were evenly discolored, whereas heat-induced bone fractures showed uneven discoloration of the fracture margin and surface. Although there were generally more heat-induced fractures in the 450-700 °C range, no other distinctive trend was observed between exposure temperature and class of fractures.