Stabbing angle alters peak force and work during sharp force trauma of porcine ribs.

Forensic anthropologists have traditionally relied on a qualitative scale (mild, moderate, severe) for describing the forces required to generate a bony injury; however, recently efforts have focused on providing more quantitative data. The current study considers the effects of blade angle on the peak force, average force, and work measured during an instrumented sharp force impact. Sixty-two porcine side ribs were stabbed with the long axis of the blade perpendicular to the convex surface and the blade edge in one of three orientations (0°, 45°, 90°). Peak force was highest when the cutting edge was perpendicular to the long axis of the rib (90°) and lowest when it was aligned (0°). Conversely, work was highest when the blade was at an oblique angle (45°) to the rib. These results confirm that the orientation of a sharp force event must be considered when estimating the mechanical loading required to generate an injury.

Development and commissioning of an instrumented pneumatic device to simulate blunt- and sharp-force trauma.

Forensic investigators commonly interpret bone fracture patterns to estimate the force required to generate that trauma. Unfortunately, these estimates are limited to qualitative values such as "mild", "moderate" or "extreme" force. This work presents a new experimental forensic device developed to simulate blunt- and sharp-force trauma injuries, while recording the forces and velocities involved, so that a more quantitative relationship between force and trauma can be established. The machine design is described in some detail, its capabilities are outlined, and the results of the commissioning and validation tests are presented. Preliminary results for both blunt- and sharp-force testing of porcine ribs, conducted at 3.8m/s, indicate the average peak force (733±95N versus 392±73N), average force (334±49N versus 101±24N), and work (2.34±0.26J versus 0.68±0.09J) are significantly higher in the blunt case. The experimental data generated by this instrumented device will allow forensic investigators to create a better quantitative link between incident conditions (velocity, force, work) and the resulting fracture patterns.

Bullet Caliber and Type Categorization from Gunshot Wounds in Sus Scrofa (Linnaeus) Long Bone.

Studies on ballistic trauma to the ribs and thorax, cranium, and long bones demonstrate the potential of obtaining a bullet caliber from an entrance wound. In order to validate prior research on caliber estimation in bone tissue and assess the viability of bullet type determination based on the macroscopic evidence at the entrance wound, thirty fleshed pork (Sus scrofa) shoulders (humeri) were shot with either lead or copper jacketed bullets in one of three calibers; 0.22, 9 mm, or 0.38. Overall, our findings are consistent with previous research indicating that calibers can be grouped into "small" and "large" categories. Bullet type, lead or copper jacket, can be ascertained based on cortical flaking and the analysis of materials deposited around the entry wound. The addition of this evidence holds value in cases where no firearm or ballistic evidence is recovered from a crime scene.

Interpreting the effects of burning on pre-incineration saw marks in bone.

This study examined the effects of fire on the features associated with saw marks in bone. Both class and individual characteristics were examined using stereomicroscopy and scanning electron microscopy (SEM). Twenty-four semifleshed Sus scrofa L. tibiae were sawed into three sections with the middle section having deep and shallow false starts. Twelve saw blades of varying age and type were each used to cut two tibiae. In each case, the first tibia was burned in an outdoor open fire to the point of partial calcination. The second tibia, our control, was macerated using a heated enzyme solution. Controls and burned specimens were examined for the following characteristics: breakaway spur, tooth hop, false start, exit chipping, tooth imprint, breakaway notch, pull out striae, kerf flare, and blade drift. In general, there was parity in the observed characteristics in the burned samples using the SEM and the stereomicroscope. SEM observation, however, provided enhanced images, with the addition of observing individual tooth imprints, previously not visible. Therefore, this study recommends using an SEM for the examination of saw cuts in burnt bone.

Establishing correspondence in wood: the challenge and some solutions?

Establishing correspondence between the upper portion of a white birch sapling, a suspected weapon, and a potential source from a stand of trees was posed to one of us (GMC). A bending force shattered the sapling, precluding physical matching. Three white birch saplings were taken from the same stand of trees in a similar manner. Correspondence was achieved by measuring the width of the annual rings along four radii from a disk cut above and below the break. The regression coefficient of the data from the two disks from the same sapling was r(2) = 0.95. Regressing the upper disk against the lower disk of two other saplings resulted in r(2) values of 0.26 and 0.17, respectively. The various characteristics that are confined to a wood stem as part of its normal process of growth can be used to eliminate candidate saplings and establish correspondence between two pieces of wood.

SEM and stereomicroscopic analysis of cut marks in fresh and burned bone.

This study documents the prevalence of cut mark characteristics in fresh and burned domestic pig ribs. Stab wounds from single edge serrated and smooth-edged knives were inflicted in the vertebral and sternal regions of each fresh rib. Each rack of ribs was then divided into vertebral and sternal units. Vertebral units were defleshed and their associated cut marks were examined using a stereomicroscope. Sternal units were burned in an outdoor fire pit and examined with the addition of a scanning electron microscope (SEM). Linear cuts, V-shaped cross-sections, mounding, hinge fractures, and wastage were all observed on burned ribs. There was an overall decrease in the prevalence of all features (up to a 40% decrease), regardless of knife type, in burned ribs. Striations within cut marks were not observed in either fresh or burned ribs. Oblique faulting and bone lifts could only be observed using the SEM. Mounding and wastage were obliterated during the burning process. Therefore, cut marks in burned bone should ideally be examined for their characteristics utilizing an SEM.

Exsanguinated blood volume estimation using fractal analysis of digital images.

The estimation of bloodstain volume using fractal analysis of digital images of passive blood stains is presented. Binary digital photos of bloodstains of known volumes (ranging from 1 to 7 mL), dispersed in a defined area, were subjected to image analysis using FracLac V. 2.0 for ImageJ. The box-counting method was used to generate a fractal dimension for each trial. A positive correlation between the generated fractal number and the volume of blood was found (R(2) = 0.99). Regression equations were produced to estimate the volume of blood in blind trials. An error rate ranging from 78% for 1 mL to 7% for 6 mL demonstrated that as the volume increases so does the accuracy of the volume estimation. This method used in the preliminary study proved that bloodstain patterns may be deconstructed into mathematical parameters, thus removing the subjective element inherent in other methods of volume estimation.

Differentiation of traumatic and heat-induced dental tissue fractures via SEM analysis.

Previous studies have examined the effects of heating on teeth; however, none have identified characteristics that allow analysts to differentiate traumatic from heat-induced fractures. This study examined our ability to discern notable differences in preincineration traumatic fractures and heat-induced fractures in postincineration dentition. Twelve anterior dental specimens were subjected to blunt force trauma while a second set were not. All 24 samples were then incinerated in a muffle furnace at a peak temperature (900°C) consistent with house fires. The specimens were subsequently examined with a scanning electron microscope to identify and compare heat-induced and traumatic fractures. The results obtained during examination yielded no differences between the features displayed by specimens that had been inflicted with preincineration trauma and those that did not. Unlike bone, distinguishing features for the differentiation of traumatic and heat-induced fractures could not be compiled.

A new digital method for the objective comparison of frontal sinuses for identification.

Use of the frontal sinuses for identification requires an objective method of comparison to meet Daubert standards. Christensen's application of Elliptical Fourier Analysis and Likelihood Ratios seems to be a viable solution for this problem. The proposed method draws upon this work and attempts to simplify its application. Variation between pairs of digitized sinus tracings was quantified by summing the difference between corresponding measurements taken from a fixed origin to the outer edge of the sinus outlines using Adobe Photoshop CS2. Same-skull and different-skull pairs were used to develop reference distributions from which the probability of unknown pairs coming from the same or a different individual was estimated. Error rates of 0% were achieved. Resulting correlation coefficients demonstrated inter-rater and test-retest reliability. Further refinement of the reference distributions and more rigorous testing of error rates should make this technique applicable to casework.

Microscopic indicators of axe and hatchet trauma in fleshed and defleshed mammalian long bones.

The characterization of wounds in bone caused by chopping weapons has been based on either semi-fleshed or defleshed specimens. This approach has not been adequately justified as reflecting actual cases involving fleshed bone. Likewise, the histological appearance of features in chopping wounds also deserves further attention. We used 11 fresh pig (Sus scrofa) articulated hind limbs, including the femur, tibia, and fibula with contiguous surrounding flesh (including an intact epidermal layer), to receive wounds using two axes and two hatchets. Scanning electron microscopy analysis of these wounds exhibited osteon pullouts in the fracture surfaces of fleshed specimens, suggesting the attenuation of force by the surrounding flesh. Lamellar separation was also exhibited at the impact sites and fracture surfaces of both fleshed and defleshed specimens. A consistently rough morphology is characteristic of fracture surfaces while impact surfaces are smooth and yielded evidence of striations from each implement.

Macroscopic analysis of axe and hatchet trauma in fleshed and defleshed mammalian long bones.

Recently, the authors have noted that many studies involving the characterization of chopping weapon wounds have used either semi-fleshed or defleshed bones (e.g., J Forensic Sci 2001; 46: 228). As these types of specimens do not reflect the full range of actual cases of postmortem dismemberment or perimortem trauma, 11 fresh pig (Sus scrofa) articulated hind limbs, with contiguous surrounding flesh, were inflicted with wounds using two axes and two hatchets. Defleshed humeri and femora were subjected to the same treatment. While there were no great differences found between the fleshed and defleshed specimens, characteristics observed including entrance site width and the presence of chattering were inconsistent with some aspects of Humphrey and Hutchinson's study (J Forensic Sci 2001; 46: 228). Further, it was found that curve transverse and spiral fractures were prevalent in femora, while longitudinal fractures were prevalent in fibulae. Hence, fracture types may play a role in characterizing some wounds caused by chopping weapons.