Fatal traumatic brain injury with electrical weapon falls
Introduction
Arrest-related-death (ARD) is a well-recognized syndrome often with no clear single pathological mechanism or obvious anatomical or toxicological basis.[1], [2] Annually there are about 800 000 arrests in which force is used in North America and approximately 800 ARDs yielding a mortality rate of about 1:1000 for a law-enforcement interaction associated with force.[3], [4] About 80% of resistant subjects have co-morbidities of mental illness, drug abuse, or intoxication; the majority have at least 2 of these.5
The conducted electrical weapon (CEW) is involved in a minority of ARDs.[2], [6] The largest manufacturer, TASER International, tracks the number of field uses based on sales and known usage patterns.7 This is continuously updated on their website and reveals 2.98 million field uses as of January 2016 (https://www.taser.com/lives-saved). There have also been 1.95 million CEW training exposures for a total of ∼5 million human CEW exposures.
Electronic control with the CEW has gained widespread acceptance as the preferred force option due to suspect injury reduction. Large prospective studies have consistently found suspect injury rate reductions of about 65%.[8], [9] Of the 310 000 annual CEW field uses, only 1 in 3500 is involved in an ARD vs. the baseline ARD rate of 1:1000. This reduction in fatality rate is consistent with prospective published data, which showed that 5.4% of CEW uses “clearly prevented the use of lethal force by police.”10 It is also consistent with a 2/3 reduction in fatal police shootings where CEW usage is not overly restricted.11
The short-duration (50–100 μs) electrical pulses applied by TASER CEWs (see Fig. 1) are intended to stimulate type A-α motor neurons, which are the nerves that control skeletal muscle contraction, but with minimal risk of stimulating cardiac muscle. This typically leads to a loss of regional muscle control and can result in a fall to the ground to end a potentially violent confrontation or suicide attempt.[12], [13]
Electrical weapons are, after all, weapons and there are indeed risks associated with their usage, including eye injuries and falls. With sufficient probe spread (30 cm in the front or 20 cm in the back) an uncontrolled fall to the ground is possible.12 The goal of our research was to analyze the risks of such falls from both analytical and epidemiological frameworks.
The relationship between the physical parameters of a fall and the risk of life-threatening injuries is complex and influenced by many factors, such as the shape and material properties of the object impacted, the exact fall kinematics, the individual anatomy, and the biomechanical tolerance of various body tissues.
The most common relevant parameter is the head injury criterion (HIC), based on the resultant head linear acceleration (or deceleration) calculated with Eq. (1).where a(t) is the resultant head linear acceleration (as a function of time) and t1 and t2 define the time interval that maximizes the HIC. The duration, (t2 - t1) is typically taken as 36 ms or 15 ms and the corresponding HIC-values are referred to as HIC36 or HIC15. Eq. (1) can be simplified as follows. Take the average deceleration to the 2.5 power and multiply times the exposure time. The probability of skull fracture (Abbreviated Injury Score ≥ 2) with a HIC15 = 700 is ∼30% for a mid-size male.
The energy equivalent head impact velocity (EEV) is a meaningful reference comparison of biomechanical head loading and defined as the head impact velocity that results from a fall if the initial state of the body (the potential as well as the kinematic energy of the head) is transformed in an undamped fall. In a person initially standing still, it is the velocity of a free fall from the height of the head center-of-gravity. With walking, running, or riding a bicycle the EEV increases accordingly (see Fig. 2).
If a forward fall occurs with braced hip and knee joints (i.e. the whole body tilts rigidly), the actual head impact velocity is well approximated by the EEV. In case of free knee-joint landings, the subject falls first on the knees and the tilting movement then occurs from a lower position of the head (see Fig. 3); this leads to a slightly lower head impact velocity and injury risk. Hajiaghamemar found a minor reduction of both head impact velocity (6.5 ms−1 vs. 6.7 ms−1, or 21 fps vs. 22 fps) and HIC15 (3300 vs. 4100) for forward falls with free vs. locked knee joints.14 A much stronger effect was observed in backward falls, where free hip movement leads to an impact in the buttocks first and the head impact is the result of the following tilting movement of the torso (see Fig. 4). The difference between this scenario and a backward fall with stiff hips was dramatic, giving a head impact velocity of 4.9 ms−1 vs. 6.8 ms−1 (16 fps vs. 22 fps) and HIC15 of 1800 vs. 4100.
The biomechanical tolerance of different skull regions varies substantially. While some facial bones can fracture well below impact force levels of 3 kN, the calvarium is more stable and, at the occiput, forces well above 10 kN can be tolerated.[15], [16], [17], [18], [19], [20], [21], [22] Forward falls have lower risks of life-threatening injuries compared to backward falls. A severe impact on the face causes fractures at moderate force levels resulting in energy absorption and a reduction of the resulting head acceleration similar to that seen with crush zones in an automobile body. The higher stability of the occiput region leads to higher accelerations and a higher risk of intracranial injuries (contre-coup contusions with subdural hematoma).
The head impact velocity in falls from a standing position can reach values exceeding 6 ms−1 (20 fps).[14], [23] Such an impact on a hard surface can cause severe or life-threatening injuries even on flat ground. The EEV for a mid-size male (body height 1.75 m) for a fall from a standing position (locked joints) is ∼5.7 ms−1 (19 fps). If the subjects runs or rides with a speed of 5 ms−1 (11 mph) and then falls, the EEV reaches ∼7.5 ms−1 (25 fps). A fall from a standing position on a platform 3 m above the head impact location results in an EEV of ∼9.5 ms−1 (31 fps). The ability to break the fall with coordinated arm movements prevents most fatalities from ground-level falls. Consistent with this, Thierauf et al. reported that the majority of fatal ground-level falls featured an alcohol-intoxicated subject.24 Injuries from ground-level falls are most commonly to the skull vault while elevated-fall injuries tend to be found at the skull base or cervical vertebrae.25
Section snippets
Methods
The inclusion criteria for our study were:
- 1.
Arrest-related or in-custody (post confinement) incident
- 2.
Death
- 3.
Electronic control was used in the relevant incident
- 4.
Decedent fell during the incident and the fall was forced by the CEW
- 5.
Traumatic brain injury (TBI) contributed to or caused the death
Co-author HEW maintains a database of worldwide CEW-proximate ARDs. It had 1030 cases (971 from USA) as of 1 Feb 2016. This ARD database has been cross-checked with the TASER International, Inc. internal ARD
Discussion
We believe that this paper represents the first methodical analysis of the death risk from falls induced by electronic control. Fox and Payne-James first reported that the majority of “definite or probable” deaths strongly associated with electronic control were the 8 cases of fatal falls that they found.30 Mangus reported 2 serious non-fatal head injuries from CEW deployments: (1) basilar skull fracture, right subarachnoid hemorrhage, and left-sided epidural hemorrhage necessitating craniotomy
Limitations
A prospective experimental study would generate superior data compared to our retrospective data. However, an experiment — designed to cause people to fall to determine what injuries or fatalities can be generated — would have difficulty obtaining ethical approvals.
There is no national database that records data in such incidents, so secondary sources are the only sources of information available to identify the relevant cases. When primary sources of data, such as autopsy reports, were
Conclusions
The use of electronic control presents a small (5.3 ± 2.6 PPM) but real risk of death from fatal traumatic brain injury. This risk exceeds the theoretical risk of electrocution. Increased age represents an independent risk factor for such fatalities.
Disclosures
MWK & CVW have been expert witnesses in law-enforcement litigation. MWK is a member of the TASER corporate and scientific advisory board who partially funded this work. HEW is a retired Police Chief.
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Cited by (29)
Medical implications of Conducted Energy Devices in law enforcement
2020, Journal of Forensic and Legal MedicineCitation Excerpt :The criminal justice literature was similarly searched using the Applied Social Sciences Index & Abstracts and the National Criminal Justice Reference Service Abstracts Database. Upon review of the literature, utilisation of the information provided (like any source) must be within the context of the setting; methodological biases (often retrospective studies), voluntary reporting of CED use, methods to identify cases46 using internet engines to search for incidents involving CEDs and conflict of interests (employment by manufacturers of a CED) are all legitimate concerns when examining papers. Azadani, Tseng, Ermakov, Marcus & Lee (2011) published a paper concluding that “studies funded by TASER® and/or written by an author affiliated with the company are substantially more likely to conclude that TASERs are safe”;104 however rather than a meta-analysis this was a simple statistical test of the likelihood of a publication reporting [CEDs are] “unlikely harmful or not harmful.”
Electrical weapons, hematocytes, and ischemic cardiovascular accidents
2020, Journal of Forensic and Legal MedicineEmergency Department Evaluation After Conducted Energy Weapon Use: Review of the Literature for the Clinician
2019, Journal of Emergency MedicineThomas A. Swift's Electric Rifle Injuries to the Eye and Ocular Adnexa: The Management of Complex Trauma
2019, Ophthalmology RetinaEye injury from electrical weapon probes: Mechanisms and treatment
2019, American Journal of Emergency MedicineCitation Excerpt :This is consistent with a 2/3 reduction in fatal police shootings where CEW usage is not overly restricted [3]. Electrical weapons are, after all, weapons, and there are indeed risks associated with their usage, including fatalities from falls and burns [4-6]. They launch probes with darts and hence there is a risk of significant eye injury.
Eye injuries from electrical weapon probes: Incidents, prevalence, and legal implications
2018, Journal of Forensic and Legal MedicineCitation Excerpt :With the present 18 case of unilateral blindness and enucleation, it appears that these penetrating eye injuries may be the dominant major crippling injury risk demonstrated with electronic control. While head-injuries from falls are reported, there have been no published estimates of non-fatal chronic brain injury so that prevalence is unknown.8,22 No court decisions on CEW-induced eye injury were found in the legal databases for the United Kingdom, Australia, and Canada.
- 1
Retired.