A preliminary study evaluating the relationship between force and incised trauma on pig rib bones

Abstract In forensic contexts, understanding of the complicated relationships between level of force, type of knife blade, and dimensions of incisions remains limited. The purpose of this research was to explore how incisions on pig rib bones vary depending on the type of knife blade and quantity of perpendicular force inflicted. A cutting rig (designed to position a bone, knife, and weights) facilitated the creation of incisions on fleshed rib bones (n = 59), defleshed rib bones (n = 77), and synthetic materials (n = 36). Five different masses of weights (measuring 4381, 8861, 13515, 18267, and 23343 g) were applied to four knife blades (two serrated and two non-serrated blades), with each combination of variables repeated thrice. 3D digital microscopy was utilized to model and measure each incision. The two-way ANOVA found significant differences in depth and length between knife types and levels of force across all sample sets (p < 0.05), with greater perpendicular forces and serrated blades creating longer and deeper cuts. These findings demonstrate that there is a complex relationship between force, type of knife blade, and the related dimensions of incisions.


Introduction
In countries such as Canada, where strict restrictions are in place to monitor the usage of firearms, the analysis of sharp force trauma (SFT), wounds created by sharp-edged or pointed tools, is important in medicolegal investigations [1][2][3][4].In forensic cases, incisions (or SFT wounds with greater length than depth) often occur as defects on the ribs or defensive wounds on the hands [5].Information gained from the analysis of incisions can be useful to forensic investigators.For instance, features of cut marks may serve as class characteristics, assisting with the classification of the type of weapon used [6,7].Furthermore, evaluations of the level of force used to create an incision may provide insight into the perpetrator's intent or possible identity via characteristics such as physical fitness, height, or weight, among others [1,4,8].These components have been individually investigated in previous studies, which have explored features of sharp force injuries that characterize classes of weapons or types of blades (i.e., tool mark analysis) [6,7,[9][10][11][12]; the biomechanics and dynamics of stabbings [13][14][15][16][17][18][19][20]; the amount of force required to penetrate human tissues, particularly skin and soft tissue [7,12,21]; and a variety of factors that can impact the level of force inflicted by a perpetrator [9,[22][23][24][25].In this study, elements of both class characteristics of incisions and level of force inflicted will be explored.
When dynamic forces are applied to bone, its biomechanical properties determine the extent to which it can withstand increased loads without breakage [21,26].The elasticity and strength provided by the composition of bone allow it to withstand a particular degree of force [21,26,27].As the level of stress (i.e., magnitude of force per unit area) increases, so will the corresponding level of strain (i.e., responding changes in the bone resulting from its elastic and plastic properties) in the bone.However, as the bone's elasticity and plasticity are unable to match the level of force inflicted, the rate of change in strain decreases under increasing levels of stress [21,26].As a result, a point of failure is eventually reached when the bone can no longer absorb energy and behave elastically, leading to breakage [21,[26][27][28].Exploring how bone responds under differing levels of force can increase understanding of its biomechanics and provide insight into how much stress can be withstood by bone before breakage occurs.
Three-dimensional (3D) techniques have increasingly been used to capture sharp force trauma wounds [5-7, 10, 29-43] due to their ability to create precise representations of anatomical structures and overcome issues of displacement and disproportionality inherent in two-dimensional (2D) techniques [44,45].3D microscopy reconstructs 3D models through focus stacking or depth from defocus, in which the microscope captures and combines high-resolution images as the stage moves through the focal plane from a low to high position, capturing the depth of the object [33,35].It is also possible to stitch adjacent areas together to create models larger than what is captured in the camera's field of view [33,35].Due to its ability to create high-resolution models that can capture depth, 3D microscopy warrants exploration in studies of incisions, as it can create accurate representations of small incisions or damage to bone.
The purpose of this research was to explore how the lengths and depths of incisions, as measured by 3D microscopy, created on pig rib bones and synthetic analogues vary depending on the type of kitchen knife and level of perpendicular force applied.In medicolegal contexts, the analysis of SFT class characteristics may identify the class of weapon or type of blade used [6,7], while evaluations of force may provide insight into the intent or possible identity of the perpetrator [1,4,8,19,25].It is hypothesized that knives with greater serration and levels of perpendicular force will create longer and deeper cuts.

Samples and equipment
All procedures were performed in compliance with relevant laws and institutional guidelines, with approval from the University of Toronto Mississauga.Since this study involved pork products intended for consumption, ethics approval was not required [46][47][48][49].As sharp force trauma frequently occurs in the thoracic region [1,50], two sets of rib bones-ten fleshed (i.e., with soft tissue) bones and ten defleshed (i.e., free of soft tissue) bones-were used in this study [51].Although human bone shares many structural and morphological similarities with pig bone, it may still respond differently to trauma [19,[52][53][54].Therefore, this study is only meant to demonstrate the value of exploring quantitative approaches to force and consider the relative differences in the results.Findings should not be directly applied to human bone.An additional set of seven rods of Synbone® synthetic material, made from polyurethane foam, was also studied.Due to the complex composition and geometry of bone, the synthetic material only served as controls, providing insight into expected observations on consistent samples and repeatability of results.
The inclusion of soft tissue in the fleshed samples is more representative of forensic contexts [5,51,55], while comparison with the defleshed samples can provide insight into how soft tissue may influence the measurements [14,15] and can ensure that no artifacts were introduced during maceration [5,55,56].Soft tissue was removed through a maceration process that involved multiple rounds of simmering in reverse osmosis water (R 2 H 2 O) and Dawn® dish soap [5,[55][56][57][58].The bones were dried in paper towel and refrigerated until testing occurred.Measurements for all bones (prior to and after maceration) and synthetic rods are included in Supplementary Information Table S1.As household kitchen knives are the most common sharp force weapons [4,59], two serrated and two non-serrated kitchen knives were utilized in this study, with measurements included in Supplementary Information Table S2 (Figure 1) [6,8,10].

Theoretical basis of force
The forces involved in the creation of incisions can be multidimensional and under the influence of a variety of factors [8].In recognition of this complexity, our study aims to explore one component of force: the force perpendicular to the bone surface (i.e., the vertical force with respect to gravity in the cutting rig), which is representative of a perpetrator pushing the knife blade down into the bone.In doing so, it is not the intention of this study to negate the effect of the tangential force (i.e., the horizontal force with respect to gravity in the test rig).On the contrary, this study aims to explore if and how the perpendicular force may impact the incisions and encourage further exploration into the role of the tangential force in the future.
Force is defined as the product of mass and acceleration.In this study, the rig is intentionally designed so that gravity can provide the perpendicular force; thus, acceleration can be represented by the consistent rate of gravity (9.8 m/s 2 ).Therefore, to alter the degree of perpendicular force, the mass must be adjusted.Five increasing levels of mass were selected, with weights equivalent to 4381, 8861, 13515, 18267, and 23343 g (approximately 10 lbs, 20 lbs, 30 lbs, 40 lbs, and 50 lbs).These levels of perpendicular force were selected based on preliminary trials, in which multiple individuals were asked to repeatedly apply downward force to the knife blade, resulting in a range between 10 to 50 lbs, as measured on a weight scale.Although these values may not capture the entire range of force that humans are capable of producing, they represent realistic levels of perpendicular force that perpetrators can apply, to the extent that some bones snapped under the weight of the perpendicular force.

Cutting rig
A cutting rig was designed to increase consistency in the movement of the knife, contact between the knife and bone, cutting angle, and location of impact [8,10,18,23,60], by (a) positioning the bone; (b) distributing the mass across the blade; (c) securing the knife; and (d) minimizing friction (Figures 2 and 3).The wooden rig consisted of two primary components: a base and a platform.The base included an adjustable slot with screws and fasteners to secure the bone, which had a slit across the surface to control the location of contact between the knife and bone, and a wooden platform, which served as a track to guide the movement of the knife in a consistent direction while minimizing friction and also allowing for the rig to be clamped to a larger surface and stabilized.The platform included a similar adjustable slot to position and secure the knife and a rod directly above the knife, onto which weights could be added.The height of the platform could be adjusted with screws and fasteners to control contact between the knife and bone, while its wheels facilitated smoother and more consistent movement along the track.

Experimental procedure
A minimum of 60 incisions (4 knives x 5 weights x 3 repeats) were manually created for each sample set.However, in some instances, the sample snapped under the perpendicular force while incisions were being created; as measurements of the incision itself could not accurately be taken, these samples were removed from analysis to ensure consistency and reliability of measurements.Overall, 59 of the 60 incisions on the fleshed rib bones (n = 59), 77 of the 83 incisions on the defleshed rib bones (n = 77), and 36 of the 60 incisions on the synthetic material were included in the analysis (n = 36).During the creation of the incisions, the knife and rib bone were secured into the cutting rig, the platform was adjusted to ensure controlled contact between the blade and bone, and weights were added to adjust the degree of perpendicular force.For each knife, a length of 10 cm from the tip of the blade was delineated, ensuring a consistent length of contact between the blade and bone.The knife was pulled backward rather than pushed forward so that contact would start at the 10 cm mark and end at the tip of the blade, allowing greater control over blade movement and minimizing variation from inconsistent contact.
In order to maximize repeatability and consistency while maintaining realistic human movement, one of the researchers (a left-handed 50-year-old male of 175 cm in stature and 82 kg in weight) created all incisions.For each incision, the 10 cm mark on the blade was placed on the external bone surface and the knife handle and platform were pulled along the track for a maximum 10 cm length of contact.Each incision was created with a single backward motion, with the blade movement perpendicular to the longitudinal axis of the bone.All rib bones and synthetic rods were photographed, and videos were filmed during the creation of each incision, which were monitored to ensure relatively consistent motion and speed in the movement of the knife (Figure 4).In between the cutting of each bone, the knives were sharpened ten times per blade side using a commercial Japanese sharpening stone to maximize the consistency of the sharpness of the blade.Inconsistencies in the sharpness of the blades were also minimized as all knives were newly purchased for the purpose of this study.

Three-dimensional (3D) microscopy
The Keyence® VHX-7000 3D Digital Microscope, equipped with high-resolution objective lenses, was used to capture 3D models of each incision at a magnification level of 200x.The Keyence® 3D Microscope application was used to measure maximum length (i.e., distance between the greatest extents of the cutmark on the bone surface) and maximum depth (i.e., distance between the deepest point of the incision and the undisturbed bone surface) of each incision [61].To measure maximum length, a marker was placed where the incision started and ended on the surface of the bone (Figure 5).To measure maximum depth, the software detected the deepest point of the incision, with markers placed at this depth and the level bone surface (Figure 6).The distance between the markers were calculated by the software.

Statistical analysis
As each dataset followed patterns of normality, parametric two-way analysis of variance (ANOVA) tests were conducted to assess whether significant variation (α = 0.05) exists between incision depth or length and degree of perpendicular force or type of knife blade [62][63][64].The sums of squares and Tukey's pairwise post-hoc tests were examined to assess the contribution of each variable and the group means primarily responsible for driving the observed variation, respectively.

Test 1: Depth of incisions
Across the fleshed, defleshed, and synthetic samples, results from the two-way ANOVA tests indicate significant variation based on the type of knife blade and amount of mass (i.e., perpendicular force), with their combined effect showing significance for the fleshed bones and synthetic materials, but not for the defleshed rib bones (Tables 1-3).Proportions from the sums of squares suggest that variation is primarily driven by the type of knife blade, accounting for 39.06% of variation for the fleshed bone, 47.78% for the defleshed bone, and 54.26% for the synthetic material.Variation is also driven by the amount of mass on the knife (18.84% for the fleshed bone, 9.61% is shown in the bottom image, with measurements of [1]: depth of incision (i.e., distance between the deepest point of the incision and the level bone surface) [2]; floor angle (i.e., angle between the slope and floor, where the incision converges) [3]; opening angle (i.e., angle between the two walls of the incision) [4]; Width of incision (i.e., distance between the two walls of the incision on the bone surface); and [5] floor width (i.e., distance between the two walls of the incision at deepest point of the cut).as this paper is focused on exploring the value of this methodology and approach, only incision length and depth have been analyzed at this point.all measurements were directly taken on the 3d microscope, by placing points or lines on the profile to indicate where measurements should be taken.
for the defleshed bone, and 11.73% for the synthetic material), the interaction between the knife blade and mass (22.92% for the fleshed bone, 12.39% for the defleshed bone, and 19.88% for the synthetic material), and other factors (17.97% for the fleshed bone, 32.01% for the defleshed bone, and 14.13% for the synthetic material).
The two serrated knives created deeper incisions than the two non-serrated knives on both the fleshed and defleshed bone samples (Figure 7).For the synthetic samples, the first serrated knife created deeper and more varied incisions, while the second serrated knife showed a limited range of depths comparable to those created by the non-serrated knives.Tukey's Post-Hoc tests indicate that significant variation between the types of knives is primarily driven by interactions between the non-serrated and serrated knives for the bone samples and by interactions involving the first serrated knife for the synthetic material.Variation between the knives is also driven by the final level of applied mass (23343 g) for the fleshed bone samples, the middle level of mass (13515 g) for the defleshed bone samples, and by differences at the first (4381 g) and second levels of mass (8861 g) for the synthetic samples.
Generally, positive trends are observed as the mass on the knife (representing perpendicular force) increases; however, these trends are not consistent.For the fleshed bone samples, the 8861 g mass and the 23343 g mass produced incisions that were, on average, not as deep as the preceding mass levels; while for the synthetic materials, the average depth at 13515 g was slightly lower than the depth at 8861 g.For the defleshed bone samples, a decrease in depth is observed at 18247 g of mass.
Since most measurements involving the first serrated knife at the greatest levels of mass (i.e., 18267 and 23343 g) led to samples snapping under vertical force and their consequent exclusion, there is an unrepresentative decrease in these graphs where the positive trend should have continued, considering that the bone was not only incised, but ultimately snapped.

Test 2: Length of incisions
The two-way ANOVA finds that the length of incisions on the fleshed bone and synthetic material shows significant variation based on knife type, mass, and their combined interaction, while the length of incisions on defleshed bone varies significantly by knife type and mass, but not by their combined effect (Tables 4-6).For the fleshed bone and synthetic samples, proportions from the sums of squares suggest that variation is primarily driven by the type of knife blade, accounting for 63.06% of variation for the fleshed bone and 58.10% for the synthetic material.Variation in the fleshed bone and synthetic samples is also driven by the amount of mass on the knife (8.39% for the fleshed bone and 28.83% for the synthetic material), the interaction between knife blade and mass (14.68% for the fleshed bone and 8.56% for the synthetic material), and other factors (12.73% for the fleshed bone and 4.51% for the synthetic material).For the defleshed rib samples, the sums of squares show that variation is primarily driven by other factors at 46.67%, while 17.60% of variation is accounted for by knife type, 19.86% by mass on the knife, and 10.92% by their interaction.
For the bone samples, the serrated knives, particularly the first serrated knife, created longer and more varied incisions relative to the non-serrated knives, while for the synthetic samples, the second serrated knife created the shortest incisions in comparison to the first serrated knife and non-serrated knives (Figure 8).Tukey's Post-Hoc test indicates that significant variation in the bone samples is driven by the two greatest levels of mass (18267 and 23343 g), while significant variation in the synthetic samples is driven by all three levels of mass included in the analysis.Variation is also driven by interactions between the serrated knives for the defleshed bones and synthetic samples, while it is driven by interactions between all combinations of knives, except for the pairing of the two serrated knives, for the fleshed bones.
Consistent positive trends are observed as the mass on the knife increases for the fleshed bone samples (with the average lengths of cuts increasing as follows: 9.24 mm, 10.07 mm, 10.70 mm, 11.84 mm, 12.16 mm) and synthetic material (with the average lengths of cuts increasing as follows: 12.79 mm, 15.73 mm, and 17.43 mm).A positive trend is also generally observed as the mass on the knife increases for the defleshed

Discussion
Although the depth and length of incisions vary significantly based on both the amount of perpendicular force and knife type, the results of this study find that the type of knife blade was generally a more influential factor in driving variation.These results demonstrate the potential for measurements of depth and length to contribute to the differentiation of knife blades and, to a lesser extent, degree of perpendicular force.

Serrated and non-serrated knives
The greater variation in the depth and length of incisions (except in the synthetic samples) created by the first serrated knife is likely due to its distinct serration pattern [65].The bread knife (S1) has a constant scalloped serration, characterized by continuous wide and large scalloped striations (Figure S1), while the chef 's knife (S2) has an alternating serration pattern, with straight edges interspersed between smaller scalloped striations (Figure S2) [65].S1 created deeper and longer incisions with chipping, splintering, or lipping, which is reflected in its wider range of depth and length measurements in addition to its lower consistency relative to the incisions created by other knives [65].The larger serration pattern of S1 facilitates greater penetration into the bone, producing incisions that are deeper; however, its larger and fewer teeth result in relatively poor grip on the bone, causing skips in contact with the surface and artefacts such as raised margins, chipping, or splintering [66].The finer serration pattern of S2 allows for better grip with the bone surface, although the blade is primarily making contact with the surface of the bone, producing more superficial but consistent incisions [66].The greater variation observed in the dimensions of S1 may be explained by the interaction between this type of blade and the bone, as the widely serrated blade can vary in its cutting action, either cutting smoothly, skimming over the surface, or changing its direction [66].

Perpendicular force
Significant variation and generally positive relationships are also observed between perpendicular force and both depth and length across all sample sets; however, the level of perpendicular force was generally less influential on these dimensions than knife type.This positive relationship is not always consistent for depth, with deviations observed among the fleshed and defleshed samples.For the fleshed bones, the deviating levels of perpendicular force show greater variation, suggesting that while the depths of some incisions may meet the trend, outliers may be present to skew the overall distribution.For the defleshed bones, the greater levels of perpendicular force deviate from the positive trend; however, as some bone samples snapped under the perpendicular force and could not be accurately included, further exploration of greater levels of perpendicular force would be more insightful.With the synthetic material, the 13515 g level of perpendicular force also showed lower average depths than expected, a surprising result as the synthetic material is the most consistent in shape and composition, suggesting the influence of other variables on depth.

Comparison of fleshed bone, defleshed bone, and synthetic samples
In comparing the different sample sets, shorter and more superficial incisions were produced on the fleshed bones, while longer and deeper incisions were produced on the defleshed bones and synthetic material.The shorter and more shallow incisions on the fleshed bones suggest that some force is absorbed by soft tissue before contact is made with the bone, supporting previous findings that soft tissue provides an additional layer through which the knife must penetrate [14,15].Furthermore, as the synthetic material cannot replicate the complex composition and biomechanical properties of bone, the deeper and longer incisions may reflect its decreased ability to absorb force [67][68][69].
In terms of consistency, the defleshed bone produced the least consistent results and showed the weakest influence from perpendicular force compared to its fleshed and synthetic counterparts.This inconsistency reinforces the importance of including soft tissue when experimentally creating sharp force trauma wounds.Previous studies [14,15] have found that soft tissue provides resistance and requires a considerable degree of force to pierce through and reach the underlying bone.The exclusion of soft tissue on the defleshed bone removes such resistance and can allow for more inconsistent factors, such as bone morphology, to cause greater variation in results.Another possibility is that the structure of the defleshed rib bone was affected in the maceration process [56,57].However, attempts were made to minimize the impacts of maceration by using gentle dish soap and simmering at lower temperatures.Furthermore, all defleshed bone samples were macerated together and exposed to the same conditions, so it is reasonable to expect that any changes in bone structure would be relatively consistent among the macerated samples.

Limitations
This study focuses primarily on the perpendicular force in an attempt to explore if and how this particular dimension of force may impact incisions.However, the perpendicular force is not the only force acting upon the knife blade as incisions are created.In particular, the tangential force primarily produced from the perpetrator moving the blade across the bone is also involved in the creation of incisions [8,20,70].This study's isolation of the perpendicular force allows for increased understanding of this particular component of force, with the weaker relationship between perpendicular force and measurements (as opposed to blade type) suggesting that the perpendicular force is not as influential.In combination with previous studies (e.g., Humphrey et al. 2017) of multidimensional force that have produced results of greater significance, the results of this study encourage further exploration of the tangential component of force, which may be a stronger driving factor in the geometry of incisions.
Although the type of knife blade and degree of perpendicular force may contribute significantly to the morphology and dimensions of incisions, these factors alone are unable to completely explain the variation observed in the incisions.Natural variation in bone geometry (e.g., differing shapes, sizes, or thickness of the ribs) alters how the knife interacts with the bone, impacting the geometry of each incision [9,25,71].Furthermore, the presence of unexpected results among the synthetic samples, which are morphologically consistent, also suggests the influence of factors unrelated to bone morphology, such as the sharpness of the blade, angle of penetration, and movement of the perpetrator, among other unknown variables [4, 8, 14-16, 18, 19, 24, 25, 72].Therefore, caution must be exercised when attempting to interpret the morphology and dimensions of incisions to draw conclusion regarding force or blade type.

Significance
In forensic contexts, class characteristics of SFT wounds can assist in narrowing down the different types of tools or blades (i.e., serrated or non-serrated) that may have been used by a perpetrator [6,7].In addition, understanding the amount of force exerted by a perpetrator can provide insight into their intent, psychological state, height, weight, physical fitness, and other factors [1,4,8].Previous studies have shown that these factors can influence the level of force inflicted by a perpetrator; therefore, evaluating these levels of force may assist in excluding or including individuals as possible perpetrators [9,[22][23][24][25].For these types of conclusions to be drawn, a considerable amount of research must be conducted to better understand the complexities of these relationships.Studies including this one contribute by incrementally deepening our understanding of the different variables involved in the creation of SFT wounds.
In medicolegal investigations, force has been evaluated by forensic experts using scaled descriptions of "mild", "moderate", and "severe" [16,23].However, due to a lack of clearly defined criteria, these qualitative descriptions of force can be interpreted subjectively and inconsistently between experts [18,73].Tool mark analysis can also encounter similar scrutiny in court, particularly when forensic scientists overextend its capabilities to identify a specific tool rather than a general class of weapon or type of blade [74].With the increased demand for reliable approaches in the interpretation of criminal evidence, there is a need to improve current methods, which starts with studies-such as the present study-that explore the variety of factors influencing the geometry of incisions.
As demonstrated in this study, 3D microscopy can serve as an effective tool for visualizing incisions and taking measurements of sharp force trauma on bone.3D microscopes create high quality and accurate models, upon which both 2D and 3D measurements can be directly taken, allowing for the geometry of sharp force trauma to be captured comprehensively [44,45].Advanced zoom and resolution capabilities also allow sharp force trauma to be examined at a greater level of detail, which may not be possible with other technologies.In addition, 3D microscopy is feasible to learn, as it operates similarly to other microscopes (with which many forensic scientists are already familiar) and includes instructions for specific features (e.g., taking measurements) on its accompanying computer program.Furthermore, objects can be captured in a relatively short amount of time depending on the object size and specifications; in this study, incisions were captured within 15 to 30 min.

Conclusion
The purpose of this research was not to characterize a trend between perpendicular force and depth or length of incisions, but to explore how relative progressions of perpendicular force and differences in knife blade can impact the dimensions of incisions.Based on the significance of our results, it is recommended that other variables and factors are also investigated, larger samples sizes are studied, the tangential component of force is also explored, and interobserver error is assessed through similar studies.Multiple independent studies, including this one, have found significant results when investigating relationships between force or blade type and measurements of incisions, emphasizing the value of exploring these complicated relationships [8,9,71].This study also demonstrates how 3D microscopy can be used to take measurements of sharp force trauma wounds on bone.Although further expansion is required, this study presents a possible direction to increase understanding of force and type of knife blade for incisions on bone in forensic contexts.

Figure 2 .
Figure2. the cutting rig, with weights secured by a rod on the platform, wheels attached to the bottom of the platform, the bone secured by fasteners, and a slit for the blade to contact the bone at a consistent location.

Figure 3 .
Figure 3. the cutting rig, showing how the knife and bone were secured by fasteners and the track upon which the platform was moved.

Figure 5 .
Figure 5. example of measured bone surface, with the Xs representing the manually placed markers and the red arrow measuring incision length.

Figure 6 .
Figure 6.example of measured bone cross-section. the top left and right images show surface views of the 3d image of the incision, with the boundary between the lightened and darkened areas (on the top left image) and the blue line with the red X's (on the top right image) indicating the deepest point of the incision, where the profile of the incision (in the bottom image) is located.the profile of the incision is shown in blue lines at the bottom of the top right image.an enlarged profile of the incision (in blue)is shown in the bottom image, with measurements of[1]: depth of incision (i.e., distance between the deepest point of the incision and the level bone surface)[2]; floor angle (i.e., angle between the slope and floor, where the incision converges)[3]; opening angle (i.e., angle between the two walls of the incision)[4]; Width of incision (i.e., distance between the two walls of the incision on the bone surface); and[5] floor width (i.e., distance between the two walls of the incision at deepest point of the cut).as this paper is focused on exploring the value of this methodology and approach, only incision length and depth have been analyzed at this point.all measurements were directly taken on the 3d microscope, by placing points or lines on the profile to indicate where measurements should be taken.

Figure 7 .
Figure 7. Graph of means depicting depth of incisions by mass on knife for (a) fleshed rib bones; (b) defleshed rib bones; and (c) synthetic material.

Figure 8 .
Figure 8. Graph of means depicting length of incisions by mass on knife on (a) fleshed rib bones; (b) defleshed rib bones; and (c) synthetic material.

Table 1 .
results of two-way anoVa for the effect of knife type, mass on knife, and their interaction for depth of incisions on fleshed rib bones.

Table 2 .
results of two-way anoVa for the effect of knife type, mass on knife, and their interaction for depth of incisions on defleshed rib bones.

Table 3 .
results of two-way anoVa for the effect of knife type, mass on knife, and their interaction for depth of incisions on synthetic material.

Table 4 .
results of two-way anoVa for the effect of knife type, mass on knife, and their interaction for length of incisions on fleshed rib bones.

Table 5 .
results of two-way anoVa for the effect of knife type, mass on knife, and their interaction for length of incisions on defleshed rib bones.

Table 6 .
results of two-way anoVa for the effect of knife type, mass on knife, and their interaction for length of incisions on synthetic material.
bones, with the average lengths of cuts increasing as follows: 10.65 mm, 11.71 mm, 11.71 mm, 16.51 mm, 15.86 mm.The average length of incisions at 8861 and 13515 g of mass are the same (11.71mm); however, more variation is observed at a mass of 13515 g.