98 results found
Rebelo EA, Grigoriadis G, Carpanen D, et al., 2021, An experimentally validated finite element model of the lower limb to investigate the efficacy of blast mitigation systems, Frontiers in Bioengineering and Biotechnology, Vol: 9, ISSN: 2296-4185
Improvised explosive devices (IEDs) used in the battlefield cause damage to vehicles and their occupants. The injury burden to the casualties is significant. The biofidelity and practicality of current methods for assessing current protection to reduce the injury severity is limited. In this study, a finite-element (FE) model of the leg was developed and validated in relevant blast-loading conditions, and then used to quantify the level of protection offered by a combat boot. An FE model of the leg of a 35 years old male cadaver was developed. The cadaveric leg was tested physically in a seated posture using a traumatic injury simulator and the results used to calibrate the FE model. The calibrated model predicted hindfoot forces that were in good correlation (using the CORrelation and Analysis or CORA tool) with data from force sensors; the average correlation and analysis rating (according to ISO18571) was 0.842. The boundary conditions of the FE model were then changed to replicate pendulum tests conducted in previous studies which impacted the leg at velocities between 4 and 6.7 m/s. The FE model results of foot compression and peak force at the proximal tibia were within the experimental corridors reported in the studies. A combat boot was then incorporated into the validated computational model. Simulations were run across a range of blast-related loading conditions. The predicted proximal tibia forces and associated risk of injury indicated that the combat boot reduced the injury severity for low severity loading cases with higher times to peak velocity. The reduction in injury risk varied between 6 and 37% for calcaneal minor injuries, and 1 and 54% for calcaneal major injuries. No injury-risk reduction was found for high severity loading cases. The validated FE model of the leg developed here was able to quantify the protection offered by a combat boot to vehicle occupants across a range of blast-related loading conditions. It can now be used as a design an
Traumatic amputation has been one of the most defining injuries associated with explosive devices. An understanding of the mechanism of injury is essential in order to reduce its incidence and devastating consequences to the individual and their support network. In this study, traumatic amputation is reproduced using high-velocity environmental debris in an animal cadaveric model. The study findings are combined with previous work to describe fully the mechanism of injury as follows. The shock wave impacts with the casualty, followed by energised projectiles (environmental debris or fragmentation) carried by the blast. These cause skin and soft tissue injury, followed by skeletal trauma which compounds to produce segmental and multifragmental fractures. A critical injury point is reached, whereby the underlying integrity of both skeletal and soft tissues of the limb has been compromised. The blast wind that follows these energised projectiles completes the amputation at the level of the disruption, and traumatic amputation occurs. These findings produce a shift in the understanding of traumatic amputation due to blast from a mechanism predominately thought mediated by primary and tertiary blast, to now include secondary blast mechanisms, and inform change for mitigative strategies.
Draper D, Newell N, Masouros S, et al., 2021, Multiscale Validation of Multiple Human Body Model Functional Spinal Units, JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 143, ISSN: 0148-0731
Carpanen D, Masouros SD, Stinner DJ, 2021, Biomechanical evaluation of a tool-less external fixator., BMJ Mil Health
INTRODUCTION: Current external fixator systems used by the US and UK military for stabilising extremity fractures require specialised tools to build a construct. The goal of obtaining and maintaining limb length and alignment is not achieved if these tools are misplaced. An alternative, tool-less system is currently available, namely the Dolphix Temporary Fixation System. The aim of this study was to compare the stiffness of the Dolphix system with the existing Hoffmann III system. METHODS: Three Hoffmann III and three Dolphix constructs were assembled on a bone (tibia) surrogate. A 30 mm fracture gap was created to simulate a comminuted proximal tibia or distal femur fracture. The constructs were then tested in cyclic axial compression once daily for 3 consecutive days. RESULTS: The length and alignment of the surrogate limb was restored following each testing cycle with both external fixation systems. The stiffness of the constructs was maintained throughout each sequential test, with the Dolphix exhibiting 54% the stiffness of the Hoffmann III construct. CONCLUSION: Given the Dolphix's performance in mechanical testing and the unique advantage of having a tool-less manual locking clamp mechanism, this tool-less system should be considered for use in the mobile austere environment.
Rankin IA, Thuy-Tien N, Carpanen D, et al., 2021, Pelvic Protection Limiting Lower Limb Flail Reduces Mortality, JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 143, ISSN: 0148-0731
Tavana S, Masouros S, Baxan N, et al., 2021, The Effect of Degeneration on Internal Strains and the Mechanism of Failure in Human Intervertebral Discs Analyzed Using Digital Volume Correlation (DVC) and Ultra-High Field MRI, Frontiers in Bioengineering and Biotechnology, Vol: 8, ISSN: 2296-4185
The intervertebral disc (IVD) plays a main role in absorbing and transmitting loads within the spinal column. Degeneration alters the structural integrity of the IVDs and causes pain, especially in the lumbar region. The objective of this study was to investigate non-invasively the effect of degeneration on human 3D lumbar IVD strains (n = 8) and the mechanism of spinal failure (n = 10) under pure axial compression using digital volume correlation (DVC) and 9.4 Tesla magnetic resonance imaging (MRI). Degenerate IVDs had higher (p < 0.05) axial strains (58% higher), maximum 3D compressive strains (43% higher), and maximum 3D shear strains (41% higher), in comparison to the non-degenerate IVDs, particularly in the lateral and posterior annulus. In both degenerate and non-degenerate IVDs, peak tensile and shear strains were observed close to the endplates. Inward bulging of the inner annulus was observed in all degenerate IVDs causing an increase in the AF compressive, tensile, and shear strains at the site of inward bulge, which may predispose it to circumferential tears (delamination). The endplate is the spine's “weak link” in pure axial compression, and the mechanism of human vertebral fracture is associated with disc degeneration. In non-degenerate IVDs the locations of failure were close to the endplate centroid, whereas in degenerate IVDs they were in peripheral regions. These findings advance the state of knowledge on mechanical changes during degeneration of the IVD, which help reduce the risk of injury, optimize treatments, and improve spinal implant designs. Additionally, these new data can be used to validate computational models.
Nguyen TT, Carpanen D, Rankin I, et al., 2020, Mapping the risk of fracture of the tibia from penetrating fragments, Frontiers in Bioengineering and Biotechnology, Vol: 8, Pages: 1-11, ISSN: 2296-4185
Penetrating injuries are commonly inflicted in attacks with explosive devices. The extremities, and especially the leg, are the most commonly affected body areas, presenting high risk of infection, slow recovery, and threat of amputation. The aim of this study was to quantify the risk of fracture to the anteromedial, posterior, and lateral aspects of the tibia from a metal fragment-simulating projectile (FSP). A gas gun system and a 0.78-g cylindrical FSP were employed to perform tests on an ovine tibia model. The results from the animal study were subsequently scaled to obtain fracture-risk curves for the human tibia using the cortical thickness ratio. The thickness of the surrounding soft tissue was also taken into account when assessing fracture risk. The lateral cortex of the tibia was found to be most susceptible tofracture,whose impact velocity at 50% risk of EF1+, EF2+, EF3+, and EF4+ fracture types –according to the modified Winquist-Hansen classification –were 174, 190, 212,and 282 m/s respectively. The findings of this study will be used to increase the fidelity of predictive models of projectile penetration.
Rankin I, Nguyen TT, Carpanen D, et al., 2020, A new understanding of the mechanism of injury to the pelvis and lower limbs in blast, Frontiers in Bioengineering and Biotechnology, Vol: 8, ISSN: 2296-4185
Dismounted complex blast injury (DCBI) has been one of the most severe forms of trauma sustained in recent conflicts. This injury has been partially attributed to limb flail; however, the full causative mechanism has not yet been fully determined. Soil ejecta has been hypothesized as a significant contributor to the injury but remains untested. In this study, a small-animal model of gas-gun mediated high velocity sand blast was used to investigate this mechanism. The results demonstrated a correlation between increasing sand blast velocity and injury patterns of worsening severity across the trauma range. This study is the first to replicate high velocity sand blast and the first model to reproduce the pattern of injury seen in DCBI. These findings are consistent with clinical and battlefield data. They represent a significant change in the understanding of blast injury, producing a new mechanistic theory of traumatic amputation. This mechanism of traumatic amputation is shown to be high velocity sand blast causing the initial tissue disruption, with the following blast wind and resultant limb flail completing the amputation. These findings implicate high velocity sand blast, in addition to limb flail, as a critical mechanism of injury in the dismounted blast casualty.
Stewart S, Tenenbaum O, Masouros S, et al., 2020, Fracture non-union rates across a century of war: a systematic review of the literature, BMJ Military Health, Vol: 166, Pages: 271-276, ISSN: 2633-3767
IntroductionFractures have been a common denominator of the injury patterns observed over the past century of warfare. The fractures typified by the blast and ballistic injuries of war lead to high rates of bone loss, soft tissue injury and infection, greatly increasing the likelihood of non-union. Despite this, no reliable treatment strategy for non-union exists. This literature review aims to explore the rates of non-union across a century of conflict and war, in order to determine whether our ability to heal the fractures of war has improved.MethodsA systematic review of the literature was conducted, evaluating the rates of union in fractures sustained in a combat environment over a one hundred year period. Only those fractures sustained through a ballistic or blast mechanism were included. The review was in accordance with the Preferred Items for Systematic Reviews and Meta-Analyses (PRISMA). Quality and bias assessment was also undertaken. ResultsThirty studies met the inclusion criteria, with a total of 3232 fractures described across fifteen different conflicts from the period 1919-2019. Male subjects made up 96% of cases, and tibial fractures predominated (39%). The lowest fracture union rate observed in a series was 50%. Linear regression analysis demonstrated that increasing years had no statistically significant impact on union rate.ConclusionFailure to improve fracture union rates is likely a result of numerous factors, including greater use of blast weaponry and better survivability of casualties. Finding novel strategies to promote fracture healing is a key defence research priority, in order to improve the rates of fractures sustained in a combat environment.
Nguyen TT, Meek G, Breeze J, et al., 2020, Gelatine backing affects the performance of single-layer ballistic-resistant materials against blast fragments, Frontiers in Bioengineering and Biotechnology, Vol: 8, Pages: 1-10, ISSN: 2296-4185
Penetrating trauma by energized fragments is the most common injury from explosive devices, the main threat in the contemporary battlefield. Such devices produce projectiles dependent upon their design, including preformed fragments, casings, glass, or stones; these are subsequently energized to high velocities and cause serious injuries to the body. Current body armor focuses on the essential coverage, which is mainly the thoracic and abdominal area, and can be heavy and cumbersome. In addition, there may be coverage gaps that can benefit from the additional protection provided by one or more layers of lightweight ballistic fabrics. This study assessed the performance of single layers of commercially available ballistic protective fabrics such as Kevlar®, Twaron®, and Dyneema®, in both woven and knitted configurations. Experiments were carried out using a custom-built gas-gun system, with a 0.78-g cylindrical steel fragment simulating projectile (FSP) as the impactor, and ballistic gelatine as the backing material. FSP velocity at 50% risk of material perforation, gelatine penetration, and high-risk wounding to soft tissue, as well as the depth of penetration (DoP) against impact velocity and the normalized energy absorption were used as metrics to rank the performance of the materials tested. Additional tests were performed to investigate the effect of not including a soft-tissue simulant backing material on the performance of the fabrics. The results show that a thin layer of ballistic material may offer meaningful protection against the penetration of this FSP. Additionally, it is essential to ensure a biofidelic boundary condition as the protective efficacy of fabrics was markedly altered by a gelatine backing.
Rankin IA, Webster CE, Gibb I, et al., 2020, Pelvic injury patterns in blast: Morbidity and mortality, JOURNAL OF TRAUMA AND ACUTE CARE SURGERY, Vol: 88, Pages: 832-838, ISSN: 2163-0755
Tavana S, Clark JN, Prior J, et al., 2020, Quantifying deformations and strains in human intervertebral discs using Digital Volume Correlation combined with MRI (DVC-MRI), Journal of Biomechanics, Vol: 102, Pages: 1-7, ISSN: 0021-9290
Physical disruptions to intervertebral discs (IVDs) can cause mechanical changes that lead to degeneration and to low back pain which affects 75% of us in our lifetimes. Quantifying the effects of these changes on internal IVD strains may lead to better preventative strategies and treatments. Digital Volume Correlation (DVC) is a non-invasive technique that divides volumetric images into subsets, and measures strains by tracking the internal patterns within them under load. Applying DVC to MRIs may allow non-invasive strain measurements. However, DVC-MRI for strain measurements in IVDs has not been used previously. The purpose of this study was to quantify the strain and deformation errors associated with DVC-MRI for measurements in human IVDs.Eight human lumbar IVDs were MRI scanned (9.4T) for a ‘zero-strain study’ (multiple unloaded scans to quantify noise within the system), and a loaded study (2mm axial compression). Three DVC methodologies: Fast-Fourier transform (FFT), direct correlation (DC), and a combination of both FFT and DC approaches were compared with subset sizes ranging from 8 to 88 voxels to establish the optimal DVC methodology and settings which were then used in the loaded study.FFT+DC was the optimal method and a subset size of 56 voxels (2520 micrometers) was found to be a good compromise between errors and spatial resolution. Displacement and strain errors did not exceed 28 µm and 3000 microstrain, respectively.These findings demonstrate that DVC-MRI can quantify internal strains within IVDs non-invasively and accurately. The method has unique potential for assessing IVD strains within patients.
Nguyen TT, Carpanen D, Stinner D, et al., 2020, The risk of fracture to the tibia from a fragment simulating projectile, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 102, ISSN: 1751-6161
Penetrating injuries due to fragments energised by an explosive event are life threatening and are associated with poor clinical and functional outcomes. The tibia is the long bone most affected in survivors of explosive events, yet the risk of penetrating injury to it has not been quantified. In this study, an injury-risk assessment of penetrating injury to the tibia was conducted using a gas-gun system with a 0.78-g cylindrical fragment simulating projectile. An ovine tibia model was used to generate the injury-risk curves and human cadaveric tests were conducted to validate and scale the results of the ovine model. The impact velocity at 50% risk (±95% confidence intervals) for EF1+, EF2+, EF3+, and EF4+ fractures to the human tibia – using the modified Winquist-Hansen classification – was 271 ± 30, 363 ± 46, 459 ± 102, and 936 ± 182 m/s, respectively. The scaling factor for the impact velocity from cadaveric ovine to human was 2.5. These findings define the protection thresholds to improve the injury outcomes for fragment penetrating injury to the tibia.
Boyle C, Carpanen D, Pandelani T, et al., 2020, Lateral pressure equalisation as a principle for designing support surfaces to prevent deep tissue pressure ulcers, PLoS One, Vol: 15, ISSN: 1932-6203
When immobile or neuropathic patients are supported by beds or chairs, their soft tissues undergo deformations that can cause pressure ulcers. Current support surfaces that redistribute under-body pressures at vulnerable body sites have not succeeded in reducing pressure ulcer prevalence. Here we show that adding a supporting lateral pressure can counter-act the deformations induced by under-body pressure, and that this ‘pressure equalisation’ approach is a more effective way to reduce ulcer-inducing deformations than current approaches based on redistributing under-body pressure.A finite element model of the seated pelvis predicts that applying a lateral pressure to the soft tissue reduces peak von Mises stress in the deep tissue by a factor of 2.4 relative to a standard cushion (from 113 kPa to 47 kPA) — a greater effect than that achieved by using a more conformable cushion, which reduced von Mises stress to 75 kPa. Combining both a conformable cushion and lateral pressure reduced peak von Mises stresses to 25 kPa. The ratio of peak lateral pressure to peak under-body pressure was shown to regulate deep tissue stress better than under-body pressure alone. By optimising the magnitude and position of lateral pressure, tissue deformations can be reduced to that induced when suspended in a fluid.Our results explain the lack of efficacy in current support surfaces and suggest a new approach to designing and evaluating support surfaces: ensuring sufficient lateral pressure is applied to counter-act under-body pressure.
Bone is one of the most highly adaptive tissues in the body, possessing the capability to alter its morphology and function in response to stimuli in its surrounding environment. The ability of bone to sense and convert external mechanical stimuli into a biochemical response, which ultimately alters the phenotype and function of the cell, is described as mechanotransduction. This review aims to describe the fundamental physiology and biomechanisms that occur to induce osteogenic adaptation of a cell following application of a physical stimulus. Considerable developments have been made in recent years in our understanding of how cells orchestrate this complex interplay of processes, and have become the focus of research in osteogenesis. We will discuss current areas of preclinical and clinical research exploring the harnessing of mechanotransductive properties of cells and applying them therapeutically, both in the context of fracture healing and de novo bone formation in situations such as nonunion.
Newell N, Carpanen D, Grigoriadis G, et al., 2019, Material properties of human lumbar intervertebral discs across strain rates, Spine Journal, Vol: 19, Pages: 2013-2024, ISSN: 1529-9430
Background context:The use of finite-element (FE) methods to study the biomechanics of the intervertebral disc (IVD) has increased over recent decades due to their ability to quantify internal stresses and strains throughout the tissue. Their accuracy is dependent upon realistic, strain-rate dependent material properties, which are challenging to acquire. Purpose:The aim of this study was to use the inverse FE technique to characterize the material properties of human lumbar IVDs across strain rates.Study Design:A human cadaveric experimental study coupled with an inverse finite element study.Methods:To predict the structural response of the IVD accurately, the material response of the constituent structures was required. Therefore, compressive experiments were conducted on 16 lumbar IVDs (39 ± 19 years) to obtain the structural response. An FE model of each of these experiments was developed and then run through an inverse FE algorithm to obtain subject-specific constituent material properties, such that the structural response was accurate.Results:Experimentally, a log-linear relationship between IVD stiffness and strain rate was observed. The material properties obtained through the subject-specific inverse FE optimization of the anulus fibrosus (AF) fiber and AF fiber ground matrix allowed a good match between the experimental and FE response. This resulted in a Young’s Modulus of AF fibers (YMAF - MPa) to strain rate (ε ̇ - /s) relationship of YMAF=31.5ln(ε ̇ )+435.5, and the C10 parameter of the Neo-Hookean material model of the AF ground matrix was found to be strain-rate independent with an average value of 0.68 MPa.Conclusions:These material properties can be used to improve the accuracy, and therefore predictive ability of FE models of the spine that are used in a wide range of research areas and clinical applications.Clinical SignificanceFinite element models can be used for many applications including investigating low-back p
Rankin IA, Thuy-Tien N, Carpanen D, et al., 2019, Restricting Lower Limb Flail is Key to Preventing Fatal Pelvic Blast Injury, ANNALS OF BIOMEDICAL ENGINEERING, Vol: 47, Pages: 2232-2240, ISSN: 0090-6964
Boyle C, Plotczyk M, Fayos Villalta S, et al., 2019, Morphology and composition play distinct and complementary roles in the tolerance of plantar skin to mechanical load, Science Advances, Vol: 5, Pages: 1-13, ISSN: 2375-2548
Plantar skin on the soles of the feet has a distinct morphology and composition that is thought to enhance its tolerance to mechanical loads, although the individual contributions of morphology and composition have never been quantified. Here, we combine multiscale mechanical testing and computational models of load bearing to quantify the mechanical environment of both plantar and nonplantar skin under load. We find that morphology and composition play distinct and complementary roles in plantar skin’s load tolerance. More specifically, the thick stratum corneum provides protection from stress-based injuries such as skin tears and blisters, while epidermal and dermal compositions provide protection from deformation-based injuries such as pressure ulcers. This work provides insights into the roles of skin morphology and composition more generally and will inform the design of engineered skin substitutes as well as the etiology of skin injury.
Carpanen D, Kedgley A, Shah D, et al., 2019, Injury risk of interphalangeal and metacarpophalangeal joints under impact loading, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 97, Pages: 306-311, ISSN: 1751-6161
Injuries to the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of the hand are particularly disabling. However, current standards for hand protection from blunt impact are not based on quantitative measures of the likelihood of damage to the tissues. The aim of this study was to evaluate the probability of injury of the MCP and PIP joints of the human hand due to blunt impact.Impact testing was conducted on 21 fresh-frozen cadaveric hands. Unconstrained motion at every joint was allowed. All hands were imaged with computed tomography and dissected post-impact to quantify injury. An injury-risk curve was developed for each joint using a Weibull distribution with dorsal impact force as the predictive variable.The injury risks for PIP joints were similar, as were those for MCP joints. The risk of injury of the MCP joints from a given applied force was significantly greater than that of the PIP joints (p = 0.0006). The axial forces with a 50% injury risk for the MCP and PIP joints were 3.0 and 4.2 kN, respectively.This is the first study to have investigated the injury tolerance of the MCP and PIP joints. The proposed injury curves can be used for assessing the likelihood of tissue damage, for designing targeted protective solutions such as gloves, and for developing more biofidelic standards for assessing these solutions.
Newell N, Carpanen D, Evans JH, et al., 2019, Mechanical function of the nucleus pulposus of the intervertebral disc under high rates of loading, Spine, Vol: 44, Pages: 1035-1041, ISSN: 0362-2436
Study Design. Bovine motion segments were used to investigate the high-rate compression response of intervertebral discs (IVD) before and after depressurising the nucleus pulposus (NP) by drilling a hole through the cranial endplate into it.Objective. To investigate the effect of depressurising the NP on the force-displacement response, and the energy absorption in IVDs when compressed at high strain rates.Summary of Background Data. The mechanical function of the gelatinous NP located in the centre of the IVDs of the spine is unclear. Removal of the NP has been shown to affect the direction of bulge of the inner anulus fibrosus (AF), but at low loading rates removal of the NP pressure does not affect the IVD's stiffness. During sports or injurious events, IVDs are commonly exposed to high loading rates, however, no studies have investigated the mechanical function of the NP at these rates.Methods. Eight bovine motion segments were used to quantify the change in pressure caused by a hole drilled through the cranial endplate into the NP, and eight segments were used to investigate the high-rate response before and after a hole was drilled into the NP.Results. The hole caused a 28.5% drop in the NP pressure. No statistically significant difference was seen in peak force, peak displacement, or energy-absorption of the intact and depressurised NP groups under impact loading. The IVDs absorbed 72% of the input energy, and there was no rate dependency in the percentage energy absorbed.Conclusions. These results demonstrate that the NP pressure does not affect the transfer of load through, or energy absorbed by, the IVD at high loading rates and the AF, rather than the NP, may play the most important role in transferring load, and absorbing energy at these rates. This should be considered when attempting surgically to restore IVD function.Level of Evidence: N/A
Nguyen TT, Masouros S, 2019, Penetration of Blast Fragments to the Thorax, International Research Council On Biomechanics Of Injury 2019
Nguyen TT, Masouros S, 2019, Penetration of Blast Fragments to the Thorax, International Research Council On Biomechanics Of Injury
Nguyen TT, Meek G, Masouros S, 2019, Blast Fragment Protection for The Extremities, Light Weight Armour for Defense & Security 2019
Boyle CJ, Carpanen D, Pandelani T, et al., 2019, Lateral pressure equalisation as a principle for designing support surfaces to prevent deep tissue pressure ulcers, Publisher: Cold Spring Harbor Laboratory
<jats:title>Abstract</jats:title><jats:p>When immobile or neuropathic patients are supported by beds or chairs, their soft tissues undergo deformations that can cause pressure ulcers. Current support surfaces that redistribute under-body pressures at vulnerable body sites have not succeeded in reducing pressure ulcer prevalence. Here we show that adding a supporting lateral pressure can counter-act the deformations induced by under-body pressure, and that this ‘pressure equalisation’ approach is a more effective way to reduce ulcer-inducing deformations than current approaches based on redistributing under-body pressure.</jats:p><jats:p>A finite element model of the seated pelvis predicts that applying a lateral pressure to the soft tissue reduces peak von Mises stress in the deep tissue by a factor of 2.4 relative to a standard cushion — a greater effect than that achieved by using a more conformable cushion. The ratio of peak lateral pressure to peak under-body pressure was shown to regulate deep tissue stress better than under-body pressure alone. By optimising the magnitude and position of lateral pressure, tissue deformations can be reduced to that induced when suspended in a fluid.</jats:p><jats:p>Our results explain the lack of efficacy in current support surfaces, and suggest a new approach to designing and evaluating support surfaces: ensuring sufficient lateral pressure is applied to counter-act under-body pressure.</jats:p>
Webster CE, Clasper J, Gibb I, et al., 2019, Environment at the time of injury determines injury patterns in pelvic blast, JOURNAL OF THE ROYAL ARMY MEDICAL CORPS, Vol: 165, Pages: 15-17, ISSN: 0035-8665
Injuries sustained due to attacks from explosive weapons are multiple in number, complex in nature, and not well characterised. Blast may cause damage to the human body by the direct effect of overpressure, penetration by highly energised fragments, and blunt trauma by violent displacements of the body. The ability to reproduce the injuries of such insults in a well-controlled fashion is essential in order to understand fully the unique mechanism by which they occur, and design better treatment and protection strategies to alleviate the resulting poor long-term outcomes. This paper reports a range of experimental platforms that have been developed for different blast injury models, their working mechanism, and main applications. These platforms include the shock tube, split-Hopkinson bars, the gas gun, drop towers and bespoke underbody blast simulators.
Grigoriadis G, Carpanen D, Webster CE, et al., 2019, Lower limb posture affects the mechanism of injury in under-body blast, Annals of Biomedical Engineering, Vol: 47, Pages: 306-316, ISSN: 0090-6964
Over 80% of wounded Service Members sustain at least one extremity injury. The 'deck-slap' foot, a product of the vehicle's floor rising rapidly when attacked by a mine to injure the limb, has been a signature injury in recent conflicts. Given the frequency and severity of these combat-related extremity injuries, they require the greatest utilisation of resources for treatment, and have caused the greatest number of disabled soldiers during recent conflicts. Most research efforts focus on occupants seated with both tibia-to-femur and tibia-to-foot angles set at 90°; it is unknown whether results obtained from these tests are applicable when alternative seated postures are adopted. To investigate this, lower limbs from anthropometric testing devices (ATDs) and post mortem human subjects (PMHSs) were loaded in three different seated postures using an under-body blast injury simulator. Using metrics that are commonly used for assessing injury, such as the axial force and the revised tibia index, the lower limb of ATDs were found to be insensitive to posture variations while the injuries sustained by the PMHS lower limbs differed in type and severity between postures. This suggests that the mechanism of injury depends on the posture and that this cannot be captured by the current injury criteria. Therefore, great care should be taken when interpreting and extrapolating results, especially in vehicle qualification tests, when postures other than the 90°-90° are of interest.
Kedgley AE, Saw TH, Segal NA, et al., 2019, Predicting meniscal tear stability across knee-joint flexion using finite-element analysis, Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 27, Pages: 206-214, ISSN: 0942-2056
Purpose: To analyse the stress distribution through longitudinal and radial meniscal tears in three tear locations in weight-bearing conditions and use it to ascertain the impact of tear location and type on the potential for healing of meniscal tears. Methods: Subject-specific finite-element models of a healthy knee under static loading at 0°, 20°, and 30° knee flexion were developed from unloaded magnetic resonance images and weight-bearing, contrast-enhanced computed tomography images. Simulations were then run after introducing tears into the anterior, posterior, and midsections of the menisci. Results: Absolute differences between the displacements of anterior and posterior segments modelled in the intact state and those quantified from in vivo weight-bearing images were less than 0.5 mm. There were tear-location-dependent differences between hoop stress distributions along the inner and outer surfaces of longitudinal tears; the longitudinal tear surfaces were compressed together to the greatest degree in the lateral meniscus and were most consistently in compression on the midsections of both menisci. Radial tears resulted in an increase in stress at the tear apex and in a consistent small compression of the tear surfaces throughout the flexion range when in the posterior segment of the lateral meniscus. Conclusions: Both the type of meniscal tear and its location within the meniscus influenced the stresses on the tear surfaces under weight bearing. Results agree with clinical observations and suggest reasons for the inverse correlation between longitudinal tear length and healing, the inferior healing ability of medial compared with lateral menisci, and the superior healing ability of radial tears in the posterior segment of the lateral meniscus compared with other radial tears. This study has shown that meniscal tear location in addition to type likely plays a crucial role in dictating the success of non-operative treatment of the menisci. T
Mildon PJ, White D, Girdlestone C, et al., 2018, Initial Adaption of the Injury Risk of the Human Leg Under High Rate Axial Loading for Use with a Hybrid III, Human Factors and Mechanical Engineering for Defense and Safety, Vol: 2, ISSN: 2509-8004
© 2018, Content includes material subject to Crown copyright (2018), Dstl. Hybrid III Anthropomorphic Test Devices (ATDs) are widely used in testing of military vehicles against Under Body Blast. The relationship, however, between the axial load through the lower leg of the Hybrid III and that through the human tibia has not been quantified. This paper describes a transfer function that relates the measurement from the lower tibia load cell of a booted Hybrid III to the axial force in a post mortem human subject (PMHS). By incorporating this transfer function into an existing injury risk function, a prediction of the likelihood of fracture within the human leg can be obtained from the Hybrid III data. By changing the values of the coefficients within the transfer function to those derived using the maximum error, rather than the average, conservative predictions of probability of fracture can also be obtained. The transfer function is based on a combination of published experimental data, new experiments, and computational modelling. This imposes limitations on the applicability of this prediction process and its accuracy: the time to peak axial force must be less than 10 ms; the accuracy of the prediction depends on the veracity of the PMHS lumped-parameter model used, and the predictions are only truly applicable to the specific boot used in this study. This tentative prediction process indicates that the 10% probability of fracture for a 55 kg female under 40 years old and for an 85 kg male under 40 years old wearing a desert combat boot is related to forces measured by the lower tibial load cell of a Hybrid III wearing the same boot of 7.2 and 11.7 kN, respectively. The transfer function suggested here is the best tool to date for interpreting Hybrid III leg forces into risk of injury to the human leg.
Mildon PJ, White D, Sedman AJ, et al., 2018, Injury Risk of the Human Leg Under High Rate Axial Loading, Human Factors and Mechanical Engineering for Defense and Safety, Vol: 2, ISSN: 2509-8004
© 2018, Content includes material subject to Crown copyright (2018), Dstl. This paper proposes a new risk function for lower limb fractures from high rate axial loading, such as that expected in under vehicle explosions. The aim is to improve the prediction of such fractures based on the loads measured by an Anthropomorphic Test Device (ATD) during blast testing. This function has been created by combining data from six different peer-reviewed post mortem human subjects (PMHS) studies. The work, which led to the risk function, considered proximal tibia force as the primary indicator of fracture, with age, sex and body mass considered as covariates. Previous studies considered age as a linear covariate to allow the elderly PMHS population results to be mapped onto a younger population. The literature review as part of this study found, however, that bone strength varies non-linearly with age. Extrapolating bone strength linearly may therefore overestimate the strength of younger populations’ lower limbs. This study uses a non-linear variation of bone strength with age and optimised parameters within this function to produce a Weibull risk curve with a minimum spread. The function described is for loads on the human; for it to be applicable in vehicle testing, there is a need to account for the response of the ATD.
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