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Protective Clothing Reduces Lower Limb Injury Severity Against Propelled Sand Debris in a Laboratory Setting

Protective Clothing Reduces Lower Limb Injury Severity Against Propelled Sand Debris in a... The contribution of energised environmental debris to injury patterns of the blast casualty is not known. The extent to which personal protective equipment (PPE) limits the injuries sustained by energised environmental debris following an explosive event is also not known. In this study, a cadaveric model exposed to a gas-gun mediated sand blast was utilised which repro- duced soft-tissue injuries representative of those seen clinically following blast. Mean sand velocity across experiments was −1 506 ± 80  ms . Cadaveric samples wearing standard-issue PPE were shown to have a reduced injury severity to sand blast 2 2 compared to control: a statistically significant reduction was seen in the total surface area (143 mm vs. 658 mm , p = 0.004) and depth of injuries (0 vs. 23 deep injuries, odds ratio = 0.0074, 95% confidence intervals 0.0004–0.1379). This study is the first to recreate wounds from propelled sand in a human cadaveric model. These findings implicate environmental debris, such as sand ejected from a blast event, as a critical mechanism of injury in the blast casualty. Tier 1 pelvic PPE was shown to reduce markedly the severity of injury. This injury mechanism should be a key focus of future research and mitigation strategies. Keywords Biomechanics · Blast injury · Military · Defence · Debris · Traumatic amputation Introduction Blast injury was the leading cause of morbidity and mortal- ity from recent conflicts in Iraq and Afghanistan, in which * Spyros D. Masouros the improvised explosive device (IED) was the weapon of s.masouros04@imperial.ac.uk choice [1]. These weapons generally originate from the Iain A. Rankin ground, and are often buried beneath the soil, resulting in i.rankin17@imperial.ac.uk extremity wounding, particularly of the lower limbs. The Thuy-Tien N. Nguyen burden of such injuries and subsequent management is sub- thuy-tien.nguyen08@imperial.ac.uk stantial [2–4]. Louise McMenemy Following detonation of an anti-personnel IED, the l.mcmenemy@imperial.ac.uk most common mechanism of wounding is penetrating John Breeze injury from energised fragments propelled by the blast j.breeze@imperial.ac.uk [5, 6]. These energised fragments may be from the explo- Jonathan C. Clasper sive device itself, or objects from the surrounding envi- jonclasper@aol.com ronment. Energised environmental fragments and debris 1 −1 Department of Bioengineering, Imperial College London, are known to travel at speeds of up to 900  ms follow- London SW7 2AZ, UK −1 ing blast, before decelerating to 600  ms or less prior Academic Department of Military Surgery and Trauma, to impacting casualties depending upon their distance Royal Centre for Defence Medicine, ICT Centre, from the device [7, 8]. Energised fragments have been Birmingham Research Park, Birmingham B15 2SQ, UK identified as a significant contributor to morbidity and Department of Trauma and Orthopaedic Surgery, Frimley Park Hospital, Surrey GU16 7UJ, UK Vol.:(0123456789) 1 3 12 Page 2 of 7 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 mortality; however, the contribution of energised envi- Materials and Methods ronmental debris, such as soil or sand, to injury is not known [5]. The tests performed used a setup for investigating injury Injuries sustained through explosive mechanisms have from sand, utilising a gas-gun system modified to deliver extensive contamination that is driven deep between tis- sandy gravel aggregate at high velocities. The experimental sue planes; this deep contamination subsequently require design and procedures were carried out in compliance with extensive debridement. Large, complex wounds as seen the Human Tissue Act 2004. Ethical approval was granted in the military blast patient contain numerous pockets from the local regional ethics committee at the Imperial Col- into which foreign contaminated material is forced [9]. lege Healthcare Tissue Bank (ethical approval number: 17/ Contamination with environmental debris is known to WA/0161). Experiments were carried out using twelve male increase the risk of bacterial and invasive fungal infec- human cadaveric thigh samples with no prior relevant injury tions (IFIs), both of which are a cause of morbidity and or pathology (median age 38  years, range 36–51  years). late mortality [10, 11]. To manage this contamination Samples were fresh frozen at − 20 °C and thawed at room requires a series of operations to remove the foreign temperature (21 ± 2 °C) for 24 h prior to testing. material, which may worsen the level of final amputa- Sand size and properties were chosen based upon NATO tion [12]. Foreign material found within blast wounds unclassified AEP-55 recommendations for typical sandy consist of ingrained mud, dirt, and sand as well as less gravel soil granulometry [16]. A sandy gravel aggregate size obvious contaminants [9]. Wounds with heavy environ- range was subsequently chosen to fall as closely as possible mental contamination from mud, dirt, and sand have been to the median value (2 mm, range 0.09–38 mm) of the ide- associated with soft tissue infection of both environmen- ally distributed particle sizes [16]. This consisted of sandy tal bacterial organisms in addition to invasive fungi [13]. gravel of which 100% passed a 1–2-mm sieve, with any sand The delayed morbidity and mortality of invasive bacterial subsequently passing a 1-mm sieve removed (the sand size and fungal infections are significant, and can result in utilised in experiments therefore ranged from 1 to 2 mm). high-level amputation or death [10, 11]. The sand was housed within a 11-g hollow polycarbonate In order to mitigate the increasing rate of soft tissue sabot weighed prior to, and following, loading it with sand. injury to the pelvis and perineum, pelvic personal pro- The sabot-sand unit was subsequently loaded into the tective equipment (PPE) was first fielded for UK service firing chamber of a double-reservoir gas-gun system. This personnel in 2010 [14]. This was provided in three hier- system utilised a 2-L reservoir charged with air or helium ®  archical tiers, designed to be worn in conjunction with and a Mylar diaphragm firing mechanism to accelerate the one another in response to the perceived threat. Tier 1 is sabot-sand unit down a 3-m-long, 32-mm-bore barrel [17]. an under-layer to be worn beneath issue combat trousers, To accelerate the sabot-sand unit to the desired velocity, covering from waist to knees. It is constructed from a the reservoir section of the gas gun was charged to a prede- jersey-type material with two layers of high-performance termined firing pressure prior to release. After release, the knitted silk protection stitched to the outside to protect sabot-sand unit accelerates down the barrel to exit into the vulnerable areas [14]. target chamber, where the sabot is separated from the sand Evidence of injury reduction from Tier 1 PPE from frag- by a stainless-steel sabot-stripper. The sabot is halted at this mentation wounds has been observed clinically as a differ - point, whilst the sand continues to travel towards the cadav- ence in the pattern of injuries suffered by personnel wearing eric sample at the intended terminal velocity. In order to Tier 1 PPE and those not [15]. These data suggest benefit simulate the distribution and spread of sand ejecta as occurs from the use of Tier 1 PPE; however, no evaluation study following blast, two interconnecting fenestrated steel fences, to date has confirmed its efficacy in mitigating the injuries separated by 10 mm and offset to one another by 50% of the sustained by energised sand or soil. Similarly, no laboratory diameter of each fenestration, were placed distal to the gas- study has previously demonstrated the mechanism of injury gun outlet and proximal to the mount (Fig. 1a). Offsetting of energised sand or soil. of the fenestrated steel fences changed the initial stream of Accordingly, the aims of this study were (1) to rep- sand delivered by the gas gun into multiple streams of differ - licate impact and injury from propelled sand as occurs ing trajectories which subsequently dispersed into a widely following blast in a human cadaveric model, utilising a distributed spread of sand (Fig. 1b); this setup achieved blast gas-gun system, and (2) to investigate the effect of Tier propagation in three dimensions and acceleration of debris 1 pelvic PPE on mitigating the injury patterns observed. and soil ejecta in all directions, which can be considered a Our hypothesis was that sand ejecta would contribute realistic simulation of the event. to the soft tissue injury seen in dismounted blast and The speed of the sand particles at the point of that Tier 1 pelvic PPE would mitigate the injury patterns impact with the sample was estimated using high-speed observed. 1 3 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 Page 3 of 7 12 Fig. 1 a Aerial view of experimental set-up showing cadaveric thigh of fenestrated fences. c Series of high-speed video images illustrating with standard-issue combat trousers (represented by model) posi- the velocity estimation of the sand cloud based on four unique points tioned within target chamber (A: proximal thigh, B: medial thigh, of the sand spread (F: front (red), FC: front-centre (blue), C: centre C: lateral thigh, D: distal thigh, E: dispersion fence). b Photographs (green), CB: centre-back (yellow)) showing the delivery of sand without (top) and with (bottom) the use photography (Phantom VEO710L, AMETEK, USA) at in a neutral resting position with an abduction angle of 30° 68,000 fps. An average velocity for the sand cloud as a from the midline (Fig. 2). The Tier 1 pelvic protection was whole was determined based upon identifying and track- worn as a whole on the cadaveric thigh, with the sand blast ing four unique points spread across the distributed sand. directed to impact with the two layers of high-performance These points varied in velocity and were chosen from the knitted silk protection (Fig. 3). front, front-centre, centre, and centre-back of the peripher- Following impact with the sand, samples were removed ies of the sand spread (Fig. 1c). Cadaveric samples were from the target chamber and taken for subsequent photog- divided into one of two groups: either wearing (1) UK Mil- raphy and dissection. A separate photograph was taken of itary Tier 1 pelvic protection [18] (knitted silk of 490 g/ each individual injury, with adjacent ruler, and the film plane m areal density) and standard-issue combat trousers or of the camera parallel to the injury to avoid parallax errors. (2) standard-issue combat trousers only (control group). Recorded injury patterns included (1) number of injuries For each individual test, a cadaveric thigh was secured in sustained, (2) surface area of injuries sustained (surface area position within the target chamber. The thigh was placed per injury and total injured surface area), and (3) maximal 1 3 12 Page 4 of 7 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 anatomical depth of injury sustained (superficial/subcutane- ous only, or deep to the subcutaneous tissues/subfascial). Image Processing and Statistical Analysis Photographed images were subsequently assessed with image processing software to calculate the surface area of injuries sustained. ImageJ was used for image processing calculations (National Institutes of Health, USA). Image scale was set, followed by tracing the outer edges of the zone of injury for each individual injury sustained to calculate the total surface area. IBM SPSS was used for statistical analysis (version 26, IBM, USA). The Mann–Whitney test was used to assess significant differences in non-parametric data between groups, including number of injuries sustained and surface area of injuries. Cross-tabulation with Pearson χ  test was used to assess significant differences in categorical variables between groups, including depth of penetration (subcutane- ous only vs. deep (subfascial)). Results Fig. 2 Experimental setup showing cadaveric thigh with standard- issue combat trousers prior to (top) and during (bottom) impact with Impact with sand resulted in soft tissue injuries to all sand debris. A: proximal thigh, B: medial thigh, C: lateral thigh, D: distal thigh, E: dispersion fence, F: propelled sand debris at point of samples. A total of fifty-one experimentally derived inju- impact ries were produced from 12 thigh samples. Mean sand mass delivered was 8.9 g ± 0.4 g with a mean velocity of −1 506 ± 80  ms . Tier 1 pelvic PPE markedly reduced the severity of injury seen vs. control: wounds deep to the sub- cutaneous tissues were eliminated (0 vs. 23, p < 0.001) and a reduction in the total surface area of injuries was seen 2 2 (median 143 mm vs. 658 mm , p = 0.004). No significant difference was seen between groups in the number of inju- ries sustained per sample (median 3, range 2–5, vs. median 5, range 3–6, p = 0.051). As detailed in Table 1, a signifi- cant reduction was seen in the total surface area of injuries 2 2 (median 143 m m , range 115–230 m m , vs. median 658 2 2 mm , range 529–1319 mm , p = 0.004) and depth of inju- ries: all penetrating injuries sustained within the Tier 1 pro- tection group remained superficial whilst the control group sustained the majority (77%) of injuries deep to the under- lying fascial layers (0 vs. 23, p < 0.001). Figure 4 displays the damage sustained by standard-issue combat trousers and silk PPE following impact. Figure 5 shows injuries more substantial in volume and depth as sustained in the control group, whilst Fig. 6 demonstrates the substantially reduced injuries seen in the PPE group. No samples within the Tier 1 protection group sustained a penetrating injury from sand ejecta deep to the subcutaneous tissues involving the under- Fig. 3 Tier 1 pelvic personal protective equipment worn on cadaveric lying fascial and muscular layers (odds ratio = 0.0074, 95% thigh; post-impact delivered to region of two-layer high-performance knitted silk protection confidence intervals 0.0004–0.1379). 1 3 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 Page 5 of 7 12 Table 1 Number, surface area, 2 Sample Surface area of injuries sustained (mm ) Total surface Total and depth of injuries sustained 2 area (mm ) deep Tier 1 pelvic protective equipment injuries 1 72 26 21 10 13 - 142 0 2 83 37 16 - - - 136 0 3 31 43 41 - - - 115 0 4 64 14 52 72 28 - 230 0 5 56 46 101 - - - 203 0 6 55 89 - - - - 144 0 Control 7 66 150* 125* 74* 92* 67* 574 5 8 54 193* 588* 54 430* - 1319 3 9 102* 66* 71* 325 83 - 647 3 10 177* 52* 47* 118* 135 - 529 4 11 949* 42 76* - - - 1067 2 12 126* 147* 110* 217* 37* 31* 668 6 Deep to subcutaneous tissues involving underlying fascial and muscular layers Fig. 4 Exemplar damage sustained by standard-issue combat trousers (left) and PPE (right) following impact with sand debris Fig. 5 Exemplar wounds sus- tained by control group follow- ing impact with sand debris 1 3 12 Page 6 of 7 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 Fig. 6 Exemplar wounds sus- tained by PPE group following impact sand debris environmental debris deep to the subcutaneous tissues Discussion results in more extensive contamination than superficial wounds, with infection and delayed amputation frequent [5, This study is the first to recreate penetrating injury from 20]. Bacterial and invasive fungal infections following blast propelled sand in a human cadaveric model as a simulacrum can result in delayed amputation or mortality [10, 11]. The for the mineral component of soil ejecta from a blast event. findings of the present study show Tier 1 PPE to reduce the Similarly, this study is the first laboratory study to quantify severity of injury sustained from impact from environmental the severity of penetrating injuries from energised environ- debris propelled by blast; this suggests a reduced probability mental debris in the thigh area and confirm the efficacy of of infection where Tier 1 PPE is worn, through a reduction Tier 1 PPE in potentially mitigating these injuries. in wounds deep to the subcutaneous tissues with decreased Tier 1 pelvic PPE was shown to reduce markedly the soft tissue disruption and deep seeding of environmental severity of injuries in the cadaveric model as quantified by contaminants. the reducing in total surface area of injuries, and depth of A limitation of this study is the choice of sand. The sand penetration. These findings highlight the importance of Tier type and size was based upon recommended values from 1 PPE use in any environment in which blast injury to the NATO/PfP AEP-55 for optimal testing conditions of a sur- limbs may occur. Our findings are in keeping with clinical rogate TNT mine, buried in water-saturated sandy gravel, for literature examining the protective benefits of Tier 1 PPE. testing blast from anti-vehicle mines [16]. It is not known Breeze et al. reported that from 174 casualties attending a whether this choice is representative of current threats and role 3 hospital in Afghanistan, those wearing Tier 1 pelvic our recommendation would be that representative debris is PPE were significantly less likely (odds ratio = 0.1049) to identified before repeating the tests presented here. Further - sustain a penetrating wound from a blast event to the pel- more, inherent limitations are associated with a cadaveric vis than those unprotected [15]. This is consistent with this study; these include over or underestimating the effect size, laboratory study where no samples within the Tier 1 protec- and assumptions made with inferring a delayed infection tion group sustained a penetrating injury from sand ejecta risk. A non-cadaveric controlled clinical study, however, is deep to the subcutaneous tissues, involving the underlying not ethically feasible. A previous observational study has fascial and muscular layers (odds ratio = 0.0074, 95% confi- shown benefit of Tier 1 PPE vs. no protection, whilst the dence intervals 0.0004–0.1379). In addition, the total injured wearing of Tier 1 PPE has been adopted for routine use [14, superficial surface area was 4.6 times smaller (143 mm vs. 15]. Future clinical studies should include comparing current 658 mm , p = 0.004) in the protection group. Tier 1 PPE to full under trouser PPE leggings, to assess the To the best of our knowledge, no previous study has rates of wound infection, delayed amputation, and mortality. quantified penetrating injury to the thigh from energised This study is the first to recreate penetrating injury environmental debris or assessed the protective benefit pro- from propelled sand in a cadaveric model. It described a vided from Tier 1 PPE. A previous study has examined the mechanism of reproducing sand blast in a laboratory setting mitigation effects of ballistic protective fabric, similar to the utilising a pressurised gas-gun system. Tier 1 silk pelvic properties of Tier 2 PPE, to sand substrate following a con- protection was shown to reduce markedly two parameters trolled explosion [19]. As sand velocity or other injurious associated with severity of injury: wounds deep to the sub- variables were not described in this study, there is insuffi- cutaneous tissues were eliminated (0 vs. 23, p < 0.001) and a cient information with which to compare our methodologies reduction in the total superficial surface area of injuries was or findings. 2 2 seen (143 mm vs. 658 mm , p = 0.004). In turn, this would Contamination following blast is extensive, as dirt and be expected to reduce the probability of infection, through other debris are propelled along tissue planes; seeding of 1 3 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 Page 7 of 7 12 5. Covey DC, Ficke J (2016) Blast and fragment injuries of the mus- decreased soft tissue disruption and deep seeding of envi- culoskeletal system. Orthop Disasters Orthop Inj Nat Disasters ronmental contaminants. These findings implicate environ- Mass Casualty Events 269–280. https:// doi. org/ 10. 1007/ 978-3- mental debris such as sand ejected from a blast event to be 662- 48950-5_ 25 a critical mechanism of injury in the blast casualty, and this 6. Edwards DS. Clasper J (2016) Blast injury mechanism. in Blast injury science and engineering 87–104 (Springer International injury mechanism should be a key focus of future research Publishin). https:// doi. org/ 10. 1007/ 978-3- 319- 21867-0_6 and mitigation strategies. 7. Tremblay J, Bergeron D, Gonzalez R. (1998) KTA1–29: Protec- tion of soft-skinned vehicle occupants from landmine effects. In: Acknowledgements This study was conducted in the Royal British Program TTCP, editor. Val-Belair, Canada Def Res Establ Val- Legion Centre for Blast Injury Studies. The authors would like to cartier, Quebec, Canada thank the Royal British Legion for their support. Tissue samples were 8. Bowyer GW (1996) Management of small fragment wounds: provided by the Imperial College Healthcare NHS Trust Tissue Bank experience from the Afghan border. J Trauma Inj Infect Crit Care (ICHTB). Other investigators may have received samples from these 40:170S-172S same tissues. 9. Taylor C, Hettiaratchy S, Jeffery SL, Evriviades D, Kay A (2009) Contemporary approaches to definitive extremity reconstruction Funding The authors received financial support from the Royal British of military wounds. Artic J R Army Med Corps. https:// doi. org/ Legion. The research was supported by the National Institute for Health 10. 1136/ jramc- 155- 04- 12 Research (NIHR) Biomedical Research Centre based at Imperial Col- 10. Brown KV, Murray CK, Clasper JC (2010) Infectious complica- lege Healthcare NHS Trust and Imperial College London. tions of combat-related mangled extremity injuries in the British All data generated or analysed during this study are included in this military. J Trauma 69:S109–S115 published article. 11. Rodriguez CJ et  al (2014) Risk factors associated with inva- sive fungal infections in combat trauma. Surg Infect (Larchmt) 15:521–526 Declarations 12. Clasper J, Ramasamy A (2013) Traumatic amputations. Br J Pain 7:67–73 Disclaimer The views expressed are those of the author(s) and not 13. Evriviades D et al (2011) Shaping the military wound: issues sur- necessarily those of the NHS, the NIHR, or the Department of Health. rounding the reconstruction of injured servicemen at the Royal Centre for Defence Medicine. Philos Trans R Soc B Biol Sci 366:219–230 Conflict of Interest The authors declare no competing interests. 14. Lewis EA, Pigott MA, Randall A, Hepper AE The development and introduction of ballistic protection of the external genitalia Open Access This article is licensed under a Creative Commons Attri- and perineum. https:// doi. org/ 10. 1136/ jramc- 2013- 000026 bution 4.0 International License, which permits use, sharing, adapta- 15. Breeze J, Allanson-Bailey LS, Hepper AE, Midwinter MJ (2015) tion, distribution and reproduction in any medium or format, as long Demonstrating the effectiveness of body armour: a pilot prospec- as you give appropriate credit to the original author(s) and the source, tive computerised surface wound mapping trial performed at the provide a link to the Creative Commons licence, and indicate if changes role 3 hospital in Afghanistan. J R Army Med Corps 161:36–41 were made. The images or other third party material in this article are 16. NATO/PfP Unclassified (2006) Procedures for evaluating the pro- included in the article's Creative Commons licence, unless indicated tection level of logistic and light armoured vehicles volume 2 for otherwise in a credit line to the material. If material is not included in mine threat. AEP-55 2, Annex C the article's Creative Commons licence and your intended use is not 17. Nguyen TTN, Tear GR, Masouros SD, Proud WG (2018) permitted by statutory regulation or exceeds the permitted use, you will Fragment penetrating injury to long bones. AIP Conf Proc need to obtain permission directly from the copyright holder. To view a 1979:312–321 copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . 18. Lewis EA, Pigott MA, Randall A, Hepper AE (2013) The devel- opment and introduction of ballistic protection of the external genitalia and perineum. J R Army Med Corps 159:i15–i17 19. Saunders C, Carr D (2018) Towards developing a test method for References military pelvic protection. J Text Inst 109:1374–1380 20. Khatod M et al (2003) Outcomes in open tibia fractures: rela- 1. Russell R, Hunt N, Delaney R (2014) The Mortality Peer Review tionship between delay in treatment and infection. J Trauma Panel: a report on the deaths on operations of UK Service person- 55:949–954 nel 2002–2013. J R Army Med Corps 160:150–154 2. Edwards DS, McMenemy L, Stapley SA, Patel HDL, Clasper JC Publisher's Note Springer Nature remains neutral with regard to (2016) 40 years of terrorist bombings—a meta-analysis of the jurisdictional claims in published maps and institutional affiliations. casualty and injury profile. Injury 47:646–652 3. Owens BD, Kragh JF, Macaitis J, Svoboda SJ, Wenke JC (2007) Characterization of extremity wounds in operation Iraqi freedom and operation enduring freedom. J Orthop Trauma 21:254–257 4. Griffiths D, Clasper J (2006) (iii) Military limb injuries/ballistic fractures. Curr Orthop 20:346–353 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Human Factors and Mechanical Engineering for Defense and Safety Springer Journals

Protective Clothing Reduces Lower Limb Injury Severity Against Propelled Sand Debris in a Laboratory Setting

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Abstract

The contribution of energised environmental debris to injury patterns of the blast casualty is not known. The extent to which personal protective equipment (PPE) limits the injuries sustained by energised environmental debris following an explosive event is also not known. In this study, a cadaveric model exposed to a gas-gun mediated sand blast was utilised which repro- duced soft-tissue injuries representative of those seen clinically following blast. Mean sand velocity across experiments was −1 506 ± 80  ms . Cadaveric samples wearing standard-issue PPE were shown to have a reduced injury severity to sand blast 2 2 compared to control: a statistically significant reduction was seen in the total surface area (143 mm vs. 658 mm , p = 0.004) and depth of injuries (0 vs. 23 deep injuries, odds ratio = 0.0074, 95% confidence intervals 0.0004–0.1379). This study is the first to recreate wounds from propelled sand in a human cadaveric model. These findings implicate environmental debris, such as sand ejected from a blast event, as a critical mechanism of injury in the blast casualty. Tier 1 pelvic PPE was shown to reduce markedly the severity of injury. This injury mechanism should be a key focus of future research and mitigation strategies. Keywords Biomechanics · Blast injury · Military · Defence · Debris · Traumatic amputation Introduction Blast injury was the leading cause of morbidity and mortal- ity from recent conflicts in Iraq and Afghanistan, in which * Spyros D. Masouros the improvised explosive device (IED) was the weapon of s.masouros04@imperial.ac.uk choice [1]. These weapons generally originate from the Iain A. Rankin ground, and are often buried beneath the soil, resulting in i.rankin17@imperial.ac.uk extremity wounding, particularly of the lower limbs. The Thuy-Tien N. Nguyen burden of such injuries and subsequent management is sub- thuy-tien.nguyen08@imperial.ac.uk stantial [2–4]. Louise McMenemy Following detonation of an anti-personnel IED, the l.mcmenemy@imperial.ac.uk most common mechanism of wounding is penetrating John Breeze injury from energised fragments propelled by the blast j.breeze@imperial.ac.uk [5, 6]. These energised fragments may be from the explo- Jonathan C. Clasper sive device itself, or objects from the surrounding envi- jonclasper@aol.com ronment. Energised environmental fragments and debris 1 −1 Department of Bioengineering, Imperial College London, are known to travel at speeds of up to 900  ms follow- London SW7 2AZ, UK −1 ing blast, before decelerating to 600  ms or less prior Academic Department of Military Surgery and Trauma, to impacting casualties depending upon their distance Royal Centre for Defence Medicine, ICT Centre, from the device [7, 8]. Energised fragments have been Birmingham Research Park, Birmingham B15 2SQ, UK identified as a significant contributor to morbidity and Department of Trauma and Orthopaedic Surgery, Frimley Park Hospital, Surrey GU16 7UJ, UK Vol.:(0123456789) 1 3 12 Page 2 of 7 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 mortality; however, the contribution of energised envi- Materials and Methods ronmental debris, such as soil or sand, to injury is not known [5]. The tests performed used a setup for investigating injury Injuries sustained through explosive mechanisms have from sand, utilising a gas-gun system modified to deliver extensive contamination that is driven deep between tis- sandy gravel aggregate at high velocities. The experimental sue planes; this deep contamination subsequently require design and procedures were carried out in compliance with extensive debridement. Large, complex wounds as seen the Human Tissue Act 2004. Ethical approval was granted in the military blast patient contain numerous pockets from the local regional ethics committee at the Imperial Col- into which foreign contaminated material is forced [9]. lege Healthcare Tissue Bank (ethical approval number: 17/ Contamination with environmental debris is known to WA/0161). Experiments were carried out using twelve male increase the risk of bacterial and invasive fungal infec- human cadaveric thigh samples with no prior relevant injury tions (IFIs), both of which are a cause of morbidity and or pathology (median age 38  years, range 36–51  years). late mortality [10, 11]. To manage this contamination Samples were fresh frozen at − 20 °C and thawed at room requires a series of operations to remove the foreign temperature (21 ± 2 °C) for 24 h prior to testing. material, which may worsen the level of final amputa- Sand size and properties were chosen based upon NATO tion [12]. Foreign material found within blast wounds unclassified AEP-55 recommendations for typical sandy consist of ingrained mud, dirt, and sand as well as less gravel soil granulometry [16]. A sandy gravel aggregate size obvious contaminants [9]. Wounds with heavy environ- range was subsequently chosen to fall as closely as possible mental contamination from mud, dirt, and sand have been to the median value (2 mm, range 0.09–38 mm) of the ide- associated with soft tissue infection of both environmen- ally distributed particle sizes [16]. This consisted of sandy tal bacterial organisms in addition to invasive fungi [13]. gravel of which 100% passed a 1–2-mm sieve, with any sand The delayed morbidity and mortality of invasive bacterial subsequently passing a 1-mm sieve removed (the sand size and fungal infections are significant, and can result in utilised in experiments therefore ranged from 1 to 2 mm). high-level amputation or death [10, 11]. The sand was housed within a 11-g hollow polycarbonate In order to mitigate the increasing rate of soft tissue sabot weighed prior to, and following, loading it with sand. injury to the pelvis and perineum, pelvic personal pro- The sabot-sand unit was subsequently loaded into the tective equipment (PPE) was first fielded for UK service firing chamber of a double-reservoir gas-gun system. This personnel in 2010 [14]. This was provided in three hier- system utilised a 2-L reservoir charged with air or helium ®  archical tiers, designed to be worn in conjunction with and a Mylar diaphragm firing mechanism to accelerate the one another in response to the perceived threat. Tier 1 is sabot-sand unit down a 3-m-long, 32-mm-bore barrel [17]. an under-layer to be worn beneath issue combat trousers, To accelerate the sabot-sand unit to the desired velocity, covering from waist to knees. It is constructed from a the reservoir section of the gas gun was charged to a prede- jersey-type material with two layers of high-performance termined firing pressure prior to release. After release, the knitted silk protection stitched to the outside to protect sabot-sand unit accelerates down the barrel to exit into the vulnerable areas [14]. target chamber, where the sabot is separated from the sand Evidence of injury reduction from Tier 1 PPE from frag- by a stainless-steel sabot-stripper. The sabot is halted at this mentation wounds has been observed clinically as a differ - point, whilst the sand continues to travel towards the cadav- ence in the pattern of injuries suffered by personnel wearing eric sample at the intended terminal velocity. In order to Tier 1 PPE and those not [15]. These data suggest benefit simulate the distribution and spread of sand ejecta as occurs from the use of Tier 1 PPE; however, no evaluation study following blast, two interconnecting fenestrated steel fences, to date has confirmed its efficacy in mitigating the injuries separated by 10 mm and offset to one another by 50% of the sustained by energised sand or soil. Similarly, no laboratory diameter of each fenestration, were placed distal to the gas- study has previously demonstrated the mechanism of injury gun outlet and proximal to the mount (Fig. 1a). Offsetting of energised sand or soil. of the fenestrated steel fences changed the initial stream of Accordingly, the aims of this study were (1) to rep- sand delivered by the gas gun into multiple streams of differ - licate impact and injury from propelled sand as occurs ing trajectories which subsequently dispersed into a widely following blast in a human cadaveric model, utilising a distributed spread of sand (Fig. 1b); this setup achieved blast gas-gun system, and (2) to investigate the effect of Tier propagation in three dimensions and acceleration of debris 1 pelvic PPE on mitigating the injury patterns observed. and soil ejecta in all directions, which can be considered a Our hypothesis was that sand ejecta would contribute realistic simulation of the event. to the soft tissue injury seen in dismounted blast and The speed of the sand particles at the point of that Tier 1 pelvic PPE would mitigate the injury patterns impact with the sample was estimated using high-speed observed. 1 3 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 Page 3 of 7 12 Fig. 1 a Aerial view of experimental set-up showing cadaveric thigh of fenestrated fences. c Series of high-speed video images illustrating with standard-issue combat trousers (represented by model) posi- the velocity estimation of the sand cloud based on four unique points tioned within target chamber (A: proximal thigh, B: medial thigh, of the sand spread (F: front (red), FC: front-centre (blue), C: centre C: lateral thigh, D: distal thigh, E: dispersion fence). b Photographs (green), CB: centre-back (yellow)) showing the delivery of sand without (top) and with (bottom) the use photography (Phantom VEO710L, AMETEK, USA) at in a neutral resting position with an abduction angle of 30° 68,000 fps. An average velocity for the sand cloud as a from the midline (Fig. 2). The Tier 1 pelvic protection was whole was determined based upon identifying and track- worn as a whole on the cadaveric thigh, with the sand blast ing four unique points spread across the distributed sand. directed to impact with the two layers of high-performance These points varied in velocity and were chosen from the knitted silk protection (Fig. 3). front, front-centre, centre, and centre-back of the peripher- Following impact with the sand, samples were removed ies of the sand spread (Fig. 1c). Cadaveric samples were from the target chamber and taken for subsequent photog- divided into one of two groups: either wearing (1) UK Mil- raphy and dissection. A separate photograph was taken of itary Tier 1 pelvic protection [18] (knitted silk of 490 g/ each individual injury, with adjacent ruler, and the film plane m areal density) and standard-issue combat trousers or of the camera parallel to the injury to avoid parallax errors. (2) standard-issue combat trousers only (control group). Recorded injury patterns included (1) number of injuries For each individual test, a cadaveric thigh was secured in sustained, (2) surface area of injuries sustained (surface area position within the target chamber. The thigh was placed per injury and total injured surface area), and (3) maximal 1 3 12 Page 4 of 7 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 anatomical depth of injury sustained (superficial/subcutane- ous only, or deep to the subcutaneous tissues/subfascial). Image Processing and Statistical Analysis Photographed images were subsequently assessed with image processing software to calculate the surface area of injuries sustained. ImageJ was used for image processing calculations (National Institutes of Health, USA). Image scale was set, followed by tracing the outer edges of the zone of injury for each individual injury sustained to calculate the total surface area. IBM SPSS was used for statistical analysis (version 26, IBM, USA). The Mann–Whitney test was used to assess significant differences in non-parametric data between groups, including number of injuries sustained and surface area of injuries. Cross-tabulation with Pearson χ  test was used to assess significant differences in categorical variables between groups, including depth of penetration (subcutane- ous only vs. deep (subfascial)). Results Fig. 2 Experimental setup showing cadaveric thigh with standard- issue combat trousers prior to (top) and during (bottom) impact with Impact with sand resulted in soft tissue injuries to all sand debris. A: proximal thigh, B: medial thigh, C: lateral thigh, D: distal thigh, E: dispersion fence, F: propelled sand debris at point of samples. A total of fifty-one experimentally derived inju- impact ries were produced from 12 thigh samples. Mean sand mass delivered was 8.9 g ± 0.4 g with a mean velocity of −1 506 ± 80  ms . Tier 1 pelvic PPE markedly reduced the severity of injury seen vs. control: wounds deep to the sub- cutaneous tissues were eliminated (0 vs. 23, p < 0.001) and a reduction in the total surface area of injuries was seen 2 2 (median 143 mm vs. 658 mm , p = 0.004). No significant difference was seen between groups in the number of inju- ries sustained per sample (median 3, range 2–5, vs. median 5, range 3–6, p = 0.051). As detailed in Table 1, a signifi- cant reduction was seen in the total surface area of injuries 2 2 (median 143 m m , range 115–230 m m , vs. median 658 2 2 mm , range 529–1319 mm , p = 0.004) and depth of inju- ries: all penetrating injuries sustained within the Tier 1 pro- tection group remained superficial whilst the control group sustained the majority (77%) of injuries deep to the under- lying fascial layers (0 vs. 23, p < 0.001). Figure 4 displays the damage sustained by standard-issue combat trousers and silk PPE following impact. Figure 5 shows injuries more substantial in volume and depth as sustained in the control group, whilst Fig. 6 demonstrates the substantially reduced injuries seen in the PPE group. No samples within the Tier 1 protection group sustained a penetrating injury from sand ejecta deep to the subcutaneous tissues involving the under- Fig. 3 Tier 1 pelvic personal protective equipment worn on cadaveric lying fascial and muscular layers (odds ratio = 0.0074, 95% thigh; post-impact delivered to region of two-layer high-performance knitted silk protection confidence intervals 0.0004–0.1379). 1 3 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 Page 5 of 7 12 Table 1 Number, surface area, 2 Sample Surface area of injuries sustained (mm ) Total surface Total and depth of injuries sustained 2 area (mm ) deep Tier 1 pelvic protective equipment injuries 1 72 26 21 10 13 - 142 0 2 83 37 16 - - - 136 0 3 31 43 41 - - - 115 0 4 64 14 52 72 28 - 230 0 5 56 46 101 - - - 203 0 6 55 89 - - - - 144 0 Control 7 66 150* 125* 74* 92* 67* 574 5 8 54 193* 588* 54 430* - 1319 3 9 102* 66* 71* 325 83 - 647 3 10 177* 52* 47* 118* 135 - 529 4 11 949* 42 76* - - - 1067 2 12 126* 147* 110* 217* 37* 31* 668 6 Deep to subcutaneous tissues involving underlying fascial and muscular layers Fig. 4 Exemplar damage sustained by standard-issue combat trousers (left) and PPE (right) following impact with sand debris Fig. 5 Exemplar wounds sus- tained by control group follow- ing impact with sand debris 1 3 12 Page 6 of 7 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 Fig. 6 Exemplar wounds sus- tained by PPE group following impact sand debris environmental debris deep to the subcutaneous tissues Discussion results in more extensive contamination than superficial wounds, with infection and delayed amputation frequent [5, This study is the first to recreate penetrating injury from 20]. Bacterial and invasive fungal infections following blast propelled sand in a human cadaveric model as a simulacrum can result in delayed amputation or mortality [10, 11]. The for the mineral component of soil ejecta from a blast event. findings of the present study show Tier 1 PPE to reduce the Similarly, this study is the first laboratory study to quantify severity of injury sustained from impact from environmental the severity of penetrating injuries from energised environ- debris propelled by blast; this suggests a reduced probability mental debris in the thigh area and confirm the efficacy of of infection where Tier 1 PPE is worn, through a reduction Tier 1 PPE in potentially mitigating these injuries. in wounds deep to the subcutaneous tissues with decreased Tier 1 pelvic PPE was shown to reduce markedly the soft tissue disruption and deep seeding of environmental severity of injuries in the cadaveric model as quantified by contaminants. the reducing in total surface area of injuries, and depth of A limitation of this study is the choice of sand. The sand penetration. These findings highlight the importance of Tier type and size was based upon recommended values from 1 PPE use in any environment in which blast injury to the NATO/PfP AEP-55 for optimal testing conditions of a sur- limbs may occur. Our findings are in keeping with clinical rogate TNT mine, buried in water-saturated sandy gravel, for literature examining the protective benefits of Tier 1 PPE. testing blast from anti-vehicle mines [16]. It is not known Breeze et al. reported that from 174 casualties attending a whether this choice is representative of current threats and role 3 hospital in Afghanistan, those wearing Tier 1 pelvic our recommendation would be that representative debris is PPE were significantly less likely (odds ratio = 0.1049) to identified before repeating the tests presented here. Further - sustain a penetrating wound from a blast event to the pel- more, inherent limitations are associated with a cadaveric vis than those unprotected [15]. This is consistent with this study; these include over or underestimating the effect size, laboratory study where no samples within the Tier 1 protec- and assumptions made with inferring a delayed infection tion group sustained a penetrating injury from sand ejecta risk. A non-cadaveric controlled clinical study, however, is deep to the subcutaneous tissues, involving the underlying not ethically feasible. A previous observational study has fascial and muscular layers (odds ratio = 0.0074, 95% confi- shown benefit of Tier 1 PPE vs. no protection, whilst the dence intervals 0.0004–0.1379). In addition, the total injured wearing of Tier 1 PPE has been adopted for routine use [14, superficial surface area was 4.6 times smaller (143 mm vs. 15]. Future clinical studies should include comparing current 658 mm , p = 0.004) in the protection group. Tier 1 PPE to full under trouser PPE leggings, to assess the To the best of our knowledge, no previous study has rates of wound infection, delayed amputation, and mortality. quantified penetrating injury to the thigh from energised This study is the first to recreate penetrating injury environmental debris or assessed the protective benefit pro- from propelled sand in a cadaveric model. It described a vided from Tier 1 PPE. A previous study has examined the mechanism of reproducing sand blast in a laboratory setting mitigation effects of ballistic protective fabric, similar to the utilising a pressurised gas-gun system. Tier 1 silk pelvic properties of Tier 2 PPE, to sand substrate following a con- protection was shown to reduce markedly two parameters trolled explosion [19]. As sand velocity or other injurious associated with severity of injury: wounds deep to the sub- variables were not described in this study, there is insuffi- cutaneous tissues were eliminated (0 vs. 23, p < 0.001) and a cient information with which to compare our methodologies reduction in the total superficial surface area of injuries was or findings. 2 2 seen (143 mm vs. 658 mm , p = 0.004). In turn, this would Contamination following blast is extensive, as dirt and be expected to reduce the probability of infection, through other debris are propelled along tissue planes; seeding of 1 3 Human Factors and Mechanical Engineering for Defense and Safety (2022) 6:12 Page 7 of 7 12 5. Covey DC, Ficke J (2016) Blast and fragment injuries of the mus- decreased soft tissue disruption and deep seeding of envi- culoskeletal system. Orthop Disasters Orthop Inj Nat Disasters ronmental contaminants. 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Bowyer GW (1996) Management of small fragment wounds: provided by the Imperial College Healthcare NHS Trust Tissue Bank experience from the Afghan border. J Trauma Inj Infect Crit Care (ICHTB). Other investigators may have received samples from these 40:170S-172S same tissues. 9. Taylor C, Hettiaratchy S, Jeffery SL, Evriviades D, Kay A (2009) Contemporary approaches to definitive extremity reconstruction Funding The authors received financial support from the Royal British of military wounds. Artic J R Army Med Corps. https:// doi. org/ Legion. The research was supported by the National Institute for Health 10. 1136/ jramc- 155- 04- 12 Research (NIHR) Biomedical Research Centre based at Imperial Col- 10. Brown KV, Murray CK, Clasper JC (2010) Infectious complica- lege Healthcare NHS Trust and Imperial College London. tions of combat-related mangled extremity injuries in the British All data generated or analysed during this study are included in this military. J Trauma 69:S109–S115 published article. 11. Rodriguez CJ et  al (2014) Risk factors associated with inva- sive fungal infections in combat trauma. Surg Infect (Larchmt) 15:521–526 Declarations 12. Clasper J, Ramasamy A (2013) Traumatic amputations. Br J Pain 7:67–73 Disclaimer The views expressed are those of the author(s) and not 13. Evriviades D et al (2011) Shaping the military wound: issues sur- necessarily those of the NHS, the NIHR, or the Department of Health. rounding the reconstruction of injured servicemen at the Royal Centre for Defence Medicine. Philos Trans R Soc B Biol Sci 366:219–230 Conflict of Interest The authors declare no competing interests. 14. 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NATO/PfP Unclassified (2006) Procedures for evaluating the pro- included in the article's Creative Commons licence, unless indicated tection level of logistic and light armoured vehicles volume 2 for otherwise in a credit line to the material. If material is not included in mine threat. AEP-55 2, Annex C the article's Creative Commons licence and your intended use is not 17. Nguyen TTN, Tear GR, Masouros SD, Proud WG (2018) permitted by statutory regulation or exceeds the permitted use, you will Fragment penetrating injury to long bones. AIP Conf Proc need to obtain permission directly from the copyright holder. To view a 1979:312–321 copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . 18. Lewis EA, Pigott MA, Randall A, Hepper AE (2013) The devel- opment and introduction of ballistic protection of the external genitalia and perineum. J R Army Med Corps 159:i15–i17 19. 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Journal

Human Factors and Mechanical Engineering for Defense and SafetySpringer Journals

Published: Dec 1, 2022

Keywords: Biomechanics; Blast injury; Military; Defence; Debris; Traumatic amputation

References