Curvilinear fractures in burned remains: an assessment of the relationship between fracture convexity and fire directionality

Burned remains present a challenge for forensic anthropologists due to the variable nature of fires, the unique way fires impact remains, and the impact of heat changes on the analysis of the remains. A topic of extensive study is the fracture patterns seen in burned remains. Curvilinear fractures are one type of fracture that was originally discussed in the context of studying the preburned state of remains (Baby, 1954; Binford, 1963; Buikstra and Swegle, 1989). These fractures are thought to be created through the kinetic energy generated as muscles shrink and pull on the periosteum, fracturing the bone below (Symes et al., 2008). The convexity of the curvilinear fracture has been theorized to indicate the direction heat moved along bone and, more specifically, points towards the direction of the heat source (Pope, 2007; Symes et al., 2008). To assess the relationship between fracture convexity and fire directionality, the limbs of four sheep were burned in pairs with the dorsal side down and the caudal end away from the origin of the fire. During the burns, video footage was recorded and observation notes were taken. Qualitative observations were summarized using the burn notes, videos, and recovered bones. These observations documented the pattern of limb destruction and movement, color and uniformity of the burn pattern per bone, and all instances of curvilinear fractures and the direction of these fractures. A total of 18 curvilinear fractures were seen on 17 of the 56 bones examined. Of these 18 fractures, 14 were convex distally which was the predicted direction and four were convex proximally. An a posteriori power analysis was conducted and found that a sample size of 32 would be needed for a repetition of this study to have high power and effect size. In this preliminary study, conclusions suggest that curvilinear fractures are not related to fire directionality but likely indicate how heat moves along a bone. With a larger sample size, there are many avenues to further assess how curvilinear fractures are created and what information they can contribute to the anthropological analysis of burned remains.