Mechanical assessment of proprietary and improvised pelvic binders for use in the prehospital environment.

INTRODUCTION: Pelvic fractures often result from high-energy trauma and are associated with a 10% mortality rate and significant morbidity. Pelvic binders are applied in suspected pelvic injury to stabilise fractured bone, decrease bleeding and potentiate tamponade. A binder must hold the pelvis with sufficient force for this effect to be achieved. This study aims to quantify the ability of proprietary and improvised pelvic binders to hold a target tensile force over time. METHODS: The ability of three proprietary and three improvised binders to hold a binding force for 2 hours was tested. A uniaxial materials testing machine was used to tension each binder to 150 N and then hold the displacement for 2 hours; the drop in tension over time was recorded for each binder. The ability to hold tension above 130 N after 2 hours was set as the metric of binder performance. RESULTS: The median tension at 2 hours was above 130 N for the SAM Pelvic Sling II and T-POD Pelvic Stabilisation Device and was below 130 N for the Prometheus Pelvic Splint, field-expedient pelvic splint (FES) and the Personal Clothing System-Multi-Terrain Pattern Combat Trousers binders. The tension in the improvised FES after 2 hours was approximately at the target 130 N; however, in 40% of the tests, it held above 130 N. CONCLUSIONS: Binders varied in their ability to maintain sufficient tension to treat a pelvic fracture over the 2-hour testing period. The FES performed well under our testing regime; with relatively low cost and weight, it represents a good alternative to proprietary binders for the austere environment.

Injury modelling for strategic planning in protecting the national infrastructure from terrorist explosive events.

Terrorist events in the form of explosive devices have occurred and remain a threat currently to the population and the infrastructure of many nations worldwide. Injuries occur from a combination of a blast wave, energised fragments, blunt trauma and burns. The relative preponderance of each injury mechanism is dependent on the type of device, distance to targets, population density and the surrounding environment, such as an enclosed space, to name but a few. One method of primary prevention of such injuries is by modification of the environment in which the explosion occurs, such as modifying population density and the design of enclosed spaces. The Human Injury Predictor (HIP) tool is a computational model which was developed to predict the pattern of injuries following an explosion with the goal to inform national injury prevention strategies from terrorist attacks. HIP currently uses algorithms to predict the effects from primary and secondary blast and allows the geometry of buildings to be incorporated. It has been validated using clinical data from the '7/7' terrorist attacks in London and the 2017 Manchester Arena terrorist event. Although the tool can be used readily, it will benefit from further development to refine injury representation, validate injury scoring and enable the prediction of triage states. The tool can assist both in the design of future buildings and methods of transport, as well as the situation of critical emergency services required in the response following a terrorist explosive event. The aim of this paper is to describe the HIP tool in its current version and provide a roadmap for optimising its utility in the future for the protection of national infrastructure and the population.

Biomechanical evaluation of a tool-less external fixator.

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.

Fracture union rates across a century of war: a systematic review of the literature.

INTRODUCTION: Fractures 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, in order to determine whether our ability to heal the fractures of war has improved. METHODS: A systematic review of the literature was conducted, evaluating the rates of union in fractures sustained in a combat environment over a 100-year period. Only those fractures sustained through a ballistic or blast mechanism were included. The review was in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Quality and bias assessment was also undertaken. RESULTS: Thirty studies met the inclusion criteria, with a total of 3232 fractures described across 15 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. CONCLUSIONS: Failure 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.

Quantifying deformations and strains in human intervertebral discs using Digital Volume Correlation combined with MRI (DVC-MRI).

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 (9.4 T) for a 'zero-strain study' (multiple unloaded scans to quantify noise within the system), and a loaded study (2 mm 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 µm) 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.

Experimental platforms to study blast injury.

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.

Environment at the time of injury determines injury patterns in pelvic blast.

The use of explosives by terrorists, or during armed conflict, remains a major global threat. Increasingly, these events occur in the civilian domain, and can potentially lead to injury and loss of life, on a very large scale. The environment at the time of detonation is known to result in different injury patterns in casualties exposed to blast, which is highly relevant to injury mitigation analyses. We describe differences in pelvic injury patterns in relation to different environments, from casualties that presented to the deployed UK military hospitals in Iraq and Afghanistan. A casualty on foot when injured typically sustains an unstable pelvic fracture pattern, which is commonly the cause of death. These casualties die from blood loss, meaning treatment in these should focus on early pelvic haemorrhage control. In contrast, casualties injured in vehicle present a different pattern, possibly caused by direct loading via the seat, which does not result in pelvic instability. Fatalities in this cohort are from injuries to other body regions, in particular the head and the torso and who may require urgent neurosurgery or thoracotomy as life-saving interventions. A different strategy is therefore required for mounted and dismounted casualties in order to increase survivors.

Biomechanics of the human intervertebral disc: A review of testing techniques and results.

Many experimental testing techniques have been adopted in order to provide an understanding of the biomechanics of the human intervertebral disc (IVD). The aim of this review article is to amalgamate results from these studies to provide readers with an overview of the studies conducted and their contribution to our current understanding of the biomechanics and function of the IVD. The overview is presented in a way that should prove useful to experimentalists and computational modellers. Mechanical properties of whole IVDs can be assessed conveniently by testing 'motion segments' comprising two vertebrae and the intervening IVD and ligaments. Neural arches should be removed if load-sharing between them and the disc is of no interest, and specimens containing more than two vertebrae are required to study 'adjacent level' effects. Mechanisms of injury (including endplate fracture and disc herniation) have been studied by applying complex loading at physiologically-relevant loading rates, whereas mechanical evaluations of surgical prostheses require slower application of standardised loading protocols. Results can be strongly influenced by the testing environment, preconditioning, loading rate, specimen age and degeneration, and spinal level. Component tissues of the disc (anulus fibrosus, nucleus pulposus, and cartilage endplates) have been studied to determine their material properties, but only the anulus has been thoroughly evaluated. Animal discs can be used as a model of human discs where uniform non-degenerate specimens are required, although differences in scale, age, and anatomy can lead to problems in interpretation.

From the battlefield to the laboratory: the use of clinical data analysis in developing models of lower limb blast injury.

A key weapon in the insurgents' armamentarium against coalition and local security forces in Iraq and Afghanistan has been the use of anti-vehicle mines and improvised explosive devices (IEDs). Often directed against vehicle-borne troops, these devices, once detonated, transfer considerable amounts of energy through the vehicle to the occupants. This results in severe lower limb injuries that are frequently limb threatening. Fundamental to designing novel mitigation strategies is a requirement to understand the injury mechanism by developing appropriate injury modelling tools that are underpinned by the analysis of contemporary battlefield casualty data. This article aims to summarise our understanding of the clinical course of lower limb blast injuries from IEDs and its value in developing unique injury modelling test-beds to evaluate and produce the next generation of protective equipment for reducing the devastating effects of blast injury.

Accurate placement of a pelvic binder improves reduction of unstable fractures of the pelvic ring.

The aim of this study was to assess the accuracy of placement of pelvic binders and to determine whether circumferential compression at the level of the greater trochanters is the best method of reducing a symphyseal diastasis. Patients were identified by a retrospective review of all pelvic radiographs performed at a military hospital over a period of 30 months. We analysed any pelvic radiograph on which the buckle of the pelvic binder was clearly visible. The patients were divided into groups according to the position of the buckle in relation to the greater trochanters: high, trochanteric or low. Reduction of the symphyseal diastasis was measured in a subgroup of patients with an open-book fracture, which consisted of an injury to the symphysis and disruption of the posterior pelvic arch (AO/OTA 61-B/C). We identified 172 radiographs with a visible pelvic binder. Five cases were excluded due to inadequate radiographs. In 83 (50%) the binder was positioned at the level of the greater trochanters. A high position was the most common site of inaccurate placement, occurring in 65 (39%). Seventeen patients were identified as a subgroup to assess the effect of the position of the binder on reduction of the diastasis. The mean gap was 2.8 times greater (mean difference 22 mm) in the high group compared with the trochanteric group (p < 0.01). Application of a pelvic binder above the level of the greater trochanters is common and is an inadequate method of reducing pelvic fractures and is likely to delay cardiovascular recovery in these seriously injured patients.

A biomechanical basis for tears of the human acetabular labrum.

OBJECTIVE: Acetabular labral tears predominantly affect young patients and are a source of hip pain in the athlete. Four causes of the initiation of labral tears have been proposed; trauma, hypolaxity of the anterior capsule, dysplasia and bony impingement. A further cause could be reduced biomechanical properties in the area most susceptible to tears. However, no work has defined these properties. DESIGN: 32 compressive and 32 tensile test samples were harvested from fresh-frozen cadaveric acetabula. The labrum was divided into eight areas to allow comparison around its circumference. Semiconfined compressive testing and tensile testing were performed at a displacement rate of 10 mm/min in a controlled environment of 100% humidity at 37 (SD 1) degrees C. SETTING: Cadaveric study. RESULTS: The mean compressive stiffness was 31.75 (SD 16.7) MPa, and the mean tensile elastic modulus was 24.7 (SD 10.8) MPa. The anterosuperior region had a significantly lower compressive elastic modulus than either of the posterior quadrants (p<0.05) and a significantly lower tensile modulus to the anterioinferior area (p<0.05). CONCLUSIONS: The biomechanical properties in the anterosuperior region may be a contributing factor to the initiation of labral tears.

Biomechanics of the meniscus-meniscal ligament construct of the knee.

The menisci of the knee act primarily to redistribute contact force across the tibio-femoral articulation. This meniscal function is achieved through a combination of the material, geometry and attachments of the menisci. The main ligaments that attach the menisci to the tibia (insertional ligaments, deep medial collateral ligament), the femur (meniscofemoral ligaments, deep medial collateral ligament) and each other (the anterior intermeniscal ligament) are the means by which the contact force between tibia and femur is distributed into hoop stresses in the menisci to reduce contact pressure at the joint. This means that the functional biomechanics of the menisci cannot be considered in isolation and should be considered as the functional biomechanics of the meniscus-meniscal ligament construct. This article presents the current knowledge on the anatomy and functional biomechanics of the meniscus and its associated ligaments. Much is known about the function of the meniscus-meniscal ligament construct; however, there still remain significant gaps in the literature in terms of the properties of the anterior intermeniscal ligament and its function, the properties of the insertional ligaments, and the most appropriate ways to reconstruct meniscal function surgically.

Tensile properties of the human glenoid labrum.

Human fresh-frozen cadaveric glenoid labrae from 16 donors were harvested and ten of these had no gross degeneration. These ten were divided into eight equal circumferential sections. Each section was cut to produce test-samples from the core layer with a cross-section of 1 x 1 mm. Tensile testing was performed within a controlled environment unit at 37 +/- 1 degrees C and 100% relative humidity. Each test-sample was precycled to a quasi-static state to alleviate the effects of deep-freezing, prior to final testing. The tangent modulus was calculated for each test-sample before and after a 5-min period of stress relaxation and at yield. The mean elastic modulus and yield stress of the glenoid labrum were 22.8 +/- 11.4 and 2.5 +/- 2.1 MPa, respectively. The anterosuperior portion had a lower elastic modulus and lower yield stress than the inferior portion (both P < 0.02). The pre-stress relaxation tangent modulus was significantly lower than the post-stress relaxation tangent modulus for all portions of the labrum. The glenoid labrum has similar tensile material properties to articular cartilage. Its elastic modulus varies around its circumference. This suggests that the labrum may encounter different forces at different positions.