Determining the Timing and Mechanism of Bone Fracture in Bovine Bone
Trauma interpretation is one of the most essential and challenging areas of
forensic anthropology. When examining bone fragments commonly encountered in real forensic anthropological casework, the ambiguity and difficulty assessing the trauma type and bone condition at the time of fracture is markedly more difficult. Traditional features used to distinguish bone condition and trauma type have included fracture surface texture and fracture angle, however, these features have not been explored in depth in terms their reliability and these observational categories remain poorly defined. In the current study, I examine fracture angles and surfaces produced from ballistic (115g 9mm FMJ and 147g HP ammunition) and blunt force trauma (10 lb. sledge hammer) on bovine long bones in different states of preservation (frozen, fresh, dry). Building on previous anthropological research and the mechanical literature, I attempt to refine the criteria of `smooth' and `rough / jagged' used to describe surface texture and attempt correlate the criteria to bone condition and trauma type. Using Microsil, a forensic casting material, I present a straightforward method for capturing and assessing surface information without the confounding features of color and moisture. Seven sampling sites were selected from each bone, four from the entrance / point of impact side and three from the exit / posterior to impact side. All fractures cast and measured were longitudinal or radial fractures.
Results of this study indicate that fracture angle does not demonstrate a statistically significant relationship with cortical bone thickness, nor does it correlate with type of trauma or bone condition. The only statistically significant relationship was between fracture angle and bone condition for fracture angles from the impact side of blunt force trauma specimens. Fracture surface characteristics do diverge among bone conditions, but not for trauma type. Qualitatively, for a single specimen, fracture angle and fracture surface characteristics appear to have limited value in the assessment of bone condition and / or trauma type. It is recommended for the determination of bone condition and trauma type that fracture angle and surface texture be not be used when analyzing single bones. Other observations, such as impact sites and projectile entries and exits, in combination with taphonomic indicators like color, staining, and context should be relied upon to describe and determine trauma type and bone condition.