An assessment of human performance in stabbing

The 21-foot principle: Effects of age and sex on knife attack characteristics

INTRODUCTION

Knives are commonly-used weapons in criminal activities and interpersonal assaults worldwide. Injury reports have identified the upper body as the most frequent location of knife injuries, and that stabbing attacks are more fatal than slashing attacks. The first two aims of the study explore whether the type of attack and attack location could be predicted from age and sex group. The following aims compared attack times between sex and age groups and evaluated the influence of subject characteristics on attack duration. The exploratory aim surveyed subjects on attack location during the scenario if the target was not wearing body armor.

METHODS

A total of 74 subjects (male: n = 40; female: n = 34) participated. Subjects were video recorded during a 21-foot (ft) attack and participated in follow-up questions and completed a push-up test to determine physical strength. Attack time (AT), concealment location, attack type, and demographic information were correlated to age group and sex.

RESULTS

Mean AT from 21 ft was 2.40 ± 0.47 s, with the fastest of 1.75 s. The most commonly observed concealment location, attack type, and attack location on the target included the right hip (n = 62), stab (n = 62), and the chest (n = 28), respectively. After controlling for push-up ability (p < 0.05), no differences were reported between any combination of sex and age group in AT from 21 ft. Push-up ability was the sole significant predictor of AT from 21 ft (p < 0.05). Twenty-eight subjects reported they purposely avoided the body armor vest during the 21 ft attack.

CONCLUSION

Law enforcement officers are encouraged to train for quick defensive or offensive responses, such as hand-to-knife combat or rapid firearm skills that can be performed in under 1.75 s. Stronger people were predicted to complete the 21 ft attack faster.

Biomechanical characteristics of slashing attack on different body parts of a dummy using a kitchen knife

BACKGROUND

Slashing attack is one of the most common ways of committing a homicide. The purpose of this study was to evaluate the biomechanical characteristics of slashing different body parts of a dummy by young males and females using a Chinese kitchen knife and thus provide scientific evidence for criminal investigations and court trials.

METHODS

A total of 12 male and 12 female college students participated in this study. Biomechanical parameters, including joint velocity, slashing velocity, slashing force, energy, and impulse, were evaluated when slashing the chest and the neck of a dummy using a Chinese kitchen knife.

RESULTS

When slashing the neck or the chest of a dummy, male participants showed higher elbow and wrist velocities (21.2% and 28.5%, respectively) as well as higher knife velocity (33.6%), slashing velocity (25.3%), slashing force (23.3%), and energy (57.6%) compared to female participants (all p < 0.05). When slashing the chest, participants showed higher shoulder, elbow, and wrist velocities (31.9%, 12.7%, and 12.6%) as well as knife velocity (3.8%), slashing velocity (7.3%), and energy (23.2%) compared to slashing the neck (all p < 0.05), regardless of gender.

CONCLUSION

Both gender and slashing position have great impact on biomechanical characteristics of the slashing movement. Our data indicate that when slashing using a Chinese kitchen knife, males may induce severer wounds than females, and slashing different body parts may generate different slashing velocity or energy. Compared to slashing position, gender may have greater influence on the biomechanical characteristics. Findings from this study may expand our knowledge about knife slashing attacks by Chinese kitchen knives as well as other knives with comparative heavy blades.

An evaluation of human stabbing performance to inform the standardisation of textile damage examinations: Do simulation trials correlate to reported stabbings?

Forensic textile damage examinations are commonly requested in cases such as stabbings. These requests often involve the testing of knives or other weapons submitted to determine if they could have caused the damage to the evidential garment. Currently a forensic practitioner conducts this testing by manually performing the stabbing action. A biomechanics performance trial was conducted to evaluate how a range of human factors contribute to the creation of textile damage by stabbing actions. Surveys of sharp force fatalities and clinical penetrative injuries reported the chest and abdomen as the most frequent target location for stab wounds. The location of the cut-type damage recorded during the trial was found to correlate to the location of stab injuries incurred during actual stabbing cases. The type of weapon had an impact on the actions undertaken. Participants mostly utilised the smaller utility and hunting knives in underarm thrusting or overarm hacking actions, whereas an overarm hacking action, or combined hacking/slashing action was performed when using the machete. The familiarity of the knife, shape of the handle and perceived risk of injury determined how the handle was held. Participants frequently stabbed into the target immediately in front of their dominant hand, however care should be taken in interpreting this in a casework scenario. The machete was used with the highest mean velocity, and the utility knife the lowest.

The cutting edge-an investigation into the pressure necessary for cutting skin with different knife blade types

Sharp force trauma is routinely encountered in forensic practice. Often the question is posed, how much pressure or energy would have been necessary to inflict a cut with a specific knife, in order to further characterize the perpetrator or determine his intent to cause harm. This paper investigates two knife blades and its individual pressures needed to cut through the epidermis and dermis. In order to examine the necessary force for cutting through the skin, we performed experiments on a piglet skin-on-gelatin phantom. Two similarly small knives-a paring knife with a serrated blade and a Swiss Army pocket knife with a smooth blade-were moved over the phantom surface using a mobile cutting apparatus with varying weight on the load arm with the knife. The depth of the cut was to be determined according to a scale from zero to three: grade 0 = no cut; grade 1 = cut into epidermis only; grade 2 = cut into dermis; grade 3 = complete transection of the entire skin. Each cut inflicted at a specific pressure force was assessed closely in order to ascertain depth, calculate the velocity, and ultimately determine the point at which a cut would inflict grade 3 damage. The smooth blade of a pocket knife needed at least 1900g pressure in order to slice through pig skin mounted on a thick gelatin block, whereas a serrated blade of a paring knife managed to cut into or through the dermis at a comparatively lower force of 700g. Our study shows that at the same cutting velocity, a significant difference in pressure is necessary to inflict the same degree of damage.

Minimum depths to essential structures in a UK military population using computed tomography: application to stab-resistant body armour

INTRODUCTION

Edged weapons are a known domestic threat to the police forces of the UK. This threat is mitigated by wearing stab-resistant body armour that is either worn overtly or covertly depending on role. Although the UK military have traditionally focused their body armour design upon ballistic and fragmentation threats, future roles may require protection against an edged weapon threat. Since 2017, UK police body armour requirements for anatomical coverage for both edged weapon and ballistic threats are now based upon the requirements of UK military. This revised coverage may need additional research to determine minimum distances to essential structures.

METHOD

Three entry locations and penetration vectors were chosen using the limited available information in the literature, in combination with a specialist in edged weapons defence. One hundred twenty CT trauma scans of male military service personnel were subsequently analysed to ascertain minimum distances from skin surface to the first structure encountered that is included in essential coverage (heart, aorta, vena cava, liver and spleen) at 3 specific entry points.

RESULTS

Individuals ranged between 18 and 46 years, with a mean body mass index of 24.8. The absolute minimum depth from skin surface to a structure within the auspice of essential coverage was 17 mm to the liver in entry point 3 and 19 mm to the heart in entry point 2.

CONCLUSIONS

Minimum distances to critical structures were significantly larger than those described in previous studies on civilians. This study will be used to supplement existing evidence to support existing UK police requirements for stab-resistant body armour. Using the weapon entry sites and vectors described in this study, overmatching to a behind armour depth of 17 mm would cover all of this population in this study.

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.

Edged weapons awareness

Edged weapons (sometimes referred to as sharp weapons or blades) are an increasing threat to military personnel, the blue light community (police, ambulance, firefighters, other first responders) and the general public worldwide. The use of edged weapons in criminal and terrorist incidents internationally means the forensic community needs an awareness of the technology of edged weapons, how they are used, the damage (clothing and wounding) that might be caused and any other forensic implications. In this paper, the magnitude of the problem is presented, prior research summarised and implications for forensic investigations discussed.

Undiagnosed impacted knife blade from a penetrative orbital injury: A case report

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The mode of entry of the foreign body was unique as well as the force required to impale and break a knife blade in bone.

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The authors present a minimally invasive technique for dealing with this type of injury and highlight its challenges.

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This case report emphasis the need for baseline radiology in cases of traumatology especially those with vague history.

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The patient was examined by multiple physicians who did not detect the foreign body which could raise medico-legal issues.

Introduction

Impacted foreign bodies in the complex maxillofacial region is uncommon and their safe removal is a challenge.

Case presentation

The authors report an unusual case of a 41 year old male patient who suffered from violence-related orbital trauma with a knife. The presence of this foreign body was not diagnosed for a period of 20 months. After proper clinical and radiologic examination it was localized and extracted in the theater in a safe controlled manner. Although the tip of the blade was left in situ, the patient had a rapid uneventful recovery and follow up.

Discussion

The path of penetration of the foreign body in presented case didn't follow the predicted patterns of orbital injury described in literature. A dilemma exists as to how aggressive such injuries should be managed. Thus the surgical approach implemented for retrieving the current foreign body was highlighted.

Conclusion

Radiographs are a crucial element for early diagnosis and proper management of foreign body injuries. Rapid postoperative recovery can be achieved with simple safe surgical retrieval maneuvers.

Australian forensic textile damage examinations - Finding a way forward since PCAST

Textile damage examinations are requested in a range of crime types such as assault, sexual assault and homicide. They typically involve the examination of clothing for damage such as cut, tear or thermal damage, often then followed by experimental scenario testing to help ascertain the cause of the damage. Understanding the underpinning science is central to the accurate interpretation of the complex mechanism of damage formation. In a stabbing incident for example, an understanding of the dynamic relationship between the knife blade, fabric and skin (or skin simulant) is critical. Recent reports, including the President's Council of Advisors on Science and Technology (PCAST) report, have scrutinised forensic feature-based comparison techniques. Whilst textile damage was not a focus area, it can be considered a feature-based evidence class, and one which is currently largely reliant upon a practitioner's opinion, experience and professional judgement. This paper will review the current state of textile damage examinations in Australia and survey research being conducted to address the issues raised in the context of the PCAST report. The central contribution of observational data to the evidence class of textile damage will also be explored, as well as some practical measures to counter the effects of cognitive bias.

How taphonomic alteration affects the detection and imaging of striations in stab wounds

Stabbing with a kitchen knife is a common method of homicide in Europe. Serrated knives may leave tool markings (striations) in tissues. Documentation of striations is necessary for their use as forensic evidence. Traditional methods (physical casting and photography) have significant limitations, and micro-computed tomography (micro-CT) has been trialled in cartilage to “virtually cast” wounds. Previous research has shown the proportion of striations in cartilage falls following decomposition. This project has investigated the effects of taphonomic alteration and documentation methods of striations in porcine skin. Fresh, decomposed, mummified, burnt and waterlogged stab wounds in a porcine analogue were excised and imaged using photography, stereo-optical microscopy and micro-CT. The proportion of striations in each taphonomic group was determined from the images by independent analysts. Striations were observed more frequently in serrated blade wounds, although they were also identified in non-serrated blade wounds. The proportion of wounds showing striations declined following decomposition. An inversely proportional linear correlation between advancing decomposition and proportion of striations existed. Dehydration (mummification and burning) rendered serrated and non-serrated blade wounds indistinguishable. Water composition affected the preservation of striations. Identification of striations gradually declined after decomposition in tap water, but persisted to a point when left in brackish water. All three techniques imaged striations; however, the optimum technique was stereo-optical microscopy due to practical advantages and specific limitations affecting photography and micro-CT. This study demonstrates the effects of taphonomic alteration on striations and suggests stereo-optical microscopy is the optimum method for their documentation.

Forces generated in stabbing attacks: an evaluation of the utility of the mild, moderate and severe scale

The commonest way of killing in the UK is by a sharp instrument. Knight reported in 1975 that it is impossible to discern with any degree of certainty the degree of force used to create a stab wound. Despite this, expert witnesses continue to approximate the degree of force used for their reports and evidence in court. It is usually subjectively categorized as mild, moderate or severe, based solely on the examination of the wound. We undertook a study considering forces generated in a range of blunt trauma actions, using a novel force plate dynamometer to measure the peak forces obtained by adult male and female volunteers. We then studied forces generated by stabbing skin simulants and porcine samples with knives and screwdrivers. Men generated more force than women during stabbings which was found to be equivalent to somewhere between the blunt trauma actions of pushing a button to a single-handed push. When asked to stab using what they thought was mild, moderate and severe force, although volunteers were able to actively decide the force used, the actual force was found to be influenced by the weapon, sex of the individual, hand used and biological/anatomical site penetrated. This study shows that the forces generated by volunteers in mild, moderate and severe stabbing tests in almost all cases were significantly greater than the forces required for skin penetration. We suggest that the use of subjective force scales is inappropriate. Rather than use of a subjective scale, we suggest that the force required in any stabbing requires investigation in four areas: the tip radius of the weapon, minimal force required for penetration, the sex of the assailant and whether the force required for penetration is greater than that that can be generated by a person stabbing. This allows for the use of an evidence-based two-tier scale to suggest the force required.

Strain rate and anisotropy effects on the tensile failure characteristics of human skin

The anisotropic failure characteristics of human skin are relatively unknown at strain rates typical in impact biomechanics. This study reports the results of an experimental protocol to quantify the effect of dynamic strain rates and the effect of sample orientation with respect to the Langer lines. Uniaxial tensile tests were carried out at three strain rates (0.06s(-1), 53s(-1), and 167s(-1)) on 33 test samples excised from the back of a fresh cadaver. The mean ultimate tensile stress, mean elastic modulus and mean strain energy increased with increasing strain rates. While the stretch ratio at ultimate tensile stress was not affected by the strain rate, it was influenced by the orientation of the samples (parallel and perpendicular to the Langer lines. The orientation of the sample also had a strong influence on the ultimate tensile stress, with a mean value of 28.0 ± 5.7 MPa for parallel samples, and 15.6 ± 5.2 MPa for perpendicular samples, and on the elastic modulus, with corresponding mean values of 160.8 MPa ± 53.2 MPa and 70.6 MPa ± 59.5 MPa. The study also pointed out the difficulties in controlling the effective applied strain rate in dynamic characterization of soft tissue and the resulting abnormal stress-strain relationships. Finally, data collected in this study can be used to develop constitutive models where high loading rates are of primary interest.

Neurologic sequelae of penetrating cervical trauma

STUDY DESIGN

Multicenter, retrospective chart analysis was performed using data housed in the trauma registries of 2 independent American College of Surgeons verified, Level I Trauma centers. The trauma registries were queried for all cases of penetrating cervical trauma. Abstracted data included age, sex, race, mechanism of injury, Glasgow Coma Scale (GCS) level on arrival, neurologic findings on arrival, zone of injury, associated injuries, imaging studies and results, operations performed, neurologic sequelae, disposition from the hospital and the presence or absence of neurologic injury, cervical spine fracture, and cervical spine immobilization.

OBJECTIVE

The purpose of this study was to determine the relationship between cervical spine immobilization and neurologic sequelae in penetrating cervical trauma.

SUMMARY OF BACKGROUND DATA

Current recommendations for cervical spine immobilization in penetrating cervical trauma developed by empiric extension of blunt trauma protocols without evidentiary support. No evidence exists to support cervical spine immobilization as a means of preventing neurologic injury progression in cases of penetrating cervical injury.

METHODS

Abstracted data were organized, entered into a database, and compared statistically. Significance was accepted for P<0.05.

RESULTS

A total of 196 patient charts formed the study cohort. Neurologic injuries either improved or remained static. No patient could be determined to have benefited from cervical spine immobilization in this study as the only 2 patients presenting with unstable cervical spine fractures were completely neurologically devastated at the time of injury. Prehospital cervical spine immobilization may have negatively affected patients with vascular and airway injuries. Decreased cervical spine immobilization rates at one institution did not affect neurologic outcome.

CONCLUSION

Cervical spine immobilization does not appear to prevent progression of neurologic injury in cases of penetrating cervical trauma. Comorbid penetrating injuries may be negatively impacted by prehospital cervical spine immobilization.

Retained knife blade: an unusual cause for headache following massive alcohol intake

Massive alcohol intake usually resolves in a banal headache. We report a case of a patient presenting with acute alcohol intoxication in which the ensuing "hangover" was due to a knife blade deeply retained in the brain parenchyma. This case underlines the unpredictability of retained foreign bodies without a high level of suspicion and a detailed description of the circumstances of admission.

The effect of knife handle shape on stabbing performance

A quantitative knowledge of stabbing ability is a pre-requisite to establishing protection standards for stab resistant body armour. In order to determine the validity of measurements it is necessary to understand all the mechanisms that determine performance. This paper describes a series of tests that were performed in order to determine the effect of handle size and shape on the forces and impact energy that could be produced during stabbing of an armoured target. It was found that the single largest variable was that of the test participants with all other variables such as handle size and shape having only slight effects on the magnitude of impact energy. The use of a finger guard or hilt was shown to increase the mean energy delivered to the target by approximately 5J compared to a handle having no guard. It was also found that the characteristics of energy delivery were strongly influenced by the position of the grip relative to this guard. This reinforces the conclusions of previous work (Horsfall et al., 1999; Chadwick et al., 1999) on the serial nature of momentum transfer during a stabbing impact.

Wounding patterns and human performance in knife attacks: optimising the protection provided by knife-resistant body armour

BACKGROUND

Stab attacks generate high loads, and to defeat them, armour needs to be of a certain thickness and stiffness. Slash attacks produce much lower loads and armour designed to defeat them can be far lighter and more flexible.

METHODS AND SUBJECTS

Phase 1: Human performance in slash attacks: 87 randomly selected students at the Royal Military College of Science were asked to make one slash attack with an instrumented blade on a vertically mounted target. No instructions on how to slash the target were given. The direction, contact forces and velocity of each attack were recorded. Phase 2: Clinical experience with edged weapon attacks: The location and severity of all penetrating injuries in patients attending the Glasgow Royal Infirmary between 1993 and 1996 were charted on anatomical figures.

RESULTS

Phase 1: Two types of human slash behaviour were evident: a 'chop and drag' blow and a 'sweep motion' type of attack. 'Chop and drag' attacks had higher peak forces and velocities than sweep attacks. Shoulder to waist blows (diagonal) accounted for 82% of attacks, 71% of attackers used a long diagonal slash with an average cut length of 34 cm and 11% used short diagonal attacks with an average cut length of 25 cm. Only 18% of attackers slashed across the body (short horizontal); the average measured cut length of this type was 28 cm. The maximum peak force for the total sample population was 212 N; the maximum velocity was 14.88 m s(-1). The 95 percentile force for the total sample population was 181 N and the velocity was 9.89 m s(-1). Phase 2: 431 of the 500 patients had been wounded with edged weapons. The average number of wounds sustained by victims in knife assaults was 2.4. The distribution of wounds by frequency and severity are presented.

CONCLUSIONS

Anti-slash protection is required for the arms, neck, shoulders, and thighs. The clinical experience of knife-attack victims provides information on the relative vulnerabilities of different regions of the body. It is anticipated that designing a tunic-type of Police uniform that is inherently stab and slash resistant will eventually replace the current obvious and often bulky extra protective vest. Attempts at making a combined garment will need to be guided by ergonomic considerations and field testing. A similar anatomical regional risk model might also be appropriate in the design of anti-ballistic armour and combined anti-ballistic and knife-resistant armour.

Intracranial stab injuries: case report and case study

Non-missile penetrating brain injuries are rare events in western countries. We report a case with lethal stab injury of the brain and identification of the weapon used in the assault by digital superimposition on CT scans taken at admission of the victim to a hospital. Furthermore, all cases with knife stab wounds of the skull between 1971 and 2000 were analyzed and compared with literature reports. Results of this study show that there is no region preference despite of differences in bone thickness, that stab wounds of the brain are almost invariably associated with multiple stab wounds to the trunk and that the wound tract may correspond to the dimensions of the blade allowing the identification of the weapon by digital image analysis.