Publications
64 results found
Tamanna R, Matthew K, Luca H, et al., 2024, Comparison of four in vitro test methods to assess nucleus pulposus replacement device expulsion risk, JOR Spine, ISSN: 2572-1143
Raftery K, Rahman T, Smith N, et al., 2024, The role of the nucleus pulposus in intervertebral disc recovery: towards improved specifications for nucleus replacement devices, Journal of Biomechanics, ISSN: 0021-9290
Tavana S, Shek C, Rahman T, et al., 2024, The influence of geometry on intervertebral disc stiffness, Journal of Biomechanics, Vol: 163, ISSN: 0021-9290
Geometry plays an important role in intervertebral disc (IVD) mechanics. Previous computational studies have found a link between IVD geometry and stiffness. However, few experimental studies have investigated this link, possibly due to difficulties in non-destructively quantifying internal geometric features. Recent advances in ultra-high resolution MRI provides the opportunity to visualise IVD features in unprecedented detail. This study aimed to quantify 3D human IVD geometries using 9.4 T MRIs and to investigate correlations between geometric variations and IVD stiffness. Thirty human lumbar motion segments (fourteen non-degenerate and sixteen degenerate) were scanned using a 9.4 T MRI and geometric parameters were measured. A 1kN compressive load was applied to each motion segment and stiffness was calculated. Degeneration caused a reduction (p < 0.05) in IVD height, a decreased nucleus-annulus area ratio, and a 1.6 ± 3.0 mm inward collapse of the inner annulus. The IVD height, anteroposterior (AP) width, lateral width, cross-sectional area, nucleus-annulus boundary curvature, and nucleus-annulus area ratio had a significant (p < 0.05) influence on IVD stiffness. Linear relationships (p < 0.05, r > 0.47) were observed between these geometric features and IVD compressive stiffness and a multivariate regression model was generated to enable stiffness to be predicted from features observable on clinical imaging (stiffness, N/mm = 6062 - (61.2 × AP width, mm) - (169.2 × IVD height, mm)). This study advances our understanding of disc structure-function relationships and how these change with degeneration, which can be used to both generate and validate more realistic computational models.
Rahman T, Tavana S, Nicoleta B, et al., 2023, Quantifying internal intervertebral disc strains to assess nucleus replacement device designs: a digital volume correlation and ultrahigh-resolution MRI study, Frontiers in Bioengineering and Biotechnology, Vol: 11, ISSN: 2296-4185
Introduction: Nucleus replacement has been proposed as a treatment to restore biomechanics and relieve pain in degenerate intervertebral discs (IVDs). Multiple nucleus replacement devices (NRDs) have been developed, however, none are currently used routinely in clinic. A better understanding of the interactions between NRDs and surrounding tissues may provide insight into the causes of implant failure and provide target properties for future NRD designs. The aim of this study was to non-invasively quantify 3D strains within the IVD through three stages of nucleus replacement surgery: intact, post-nuclectomy, and post-treatment.Methods: Digital volume correlation (DVC) combined with 9.4T MRI was used to measure strains in seven human cadaveric specimens (42 ± 18 years) when axially compressed to 1 kN. Nucleus material was removed from each specimen creating a cavity that was filled with a hydrogel-based NRD.Results: Nucleus removal led to loss of disc height (12.6 ± 4.4%, p = 0.004) which was restored post-treatment (within 5.3 ± 3.1% of the intact state, p > 0.05). Nuclectomy led to increased circumferential strains in the lateral annulus region compared to the intact state (−4.0 ± 3.4% vs. 1.7 ± 6.0%, p = 0.013), and increased maximum shear strains in the posterior annulus region (14.6 ± 1.7% vs. 19.4 ± 2.6%, p = 0.021). In both cases, the NRD was able to restore these strain values to their intact levels (p ≥ 0.192).Discussion: The ability of the NRD to restore IVD biomechanics and some strain types to intact state levels supports nucleus replacement surgery as a viable treatment option. The DVC-MRI method used in the present study could serve as a useful tool to assess future NRD designs to help improve performance in future clinical trials.
Tavana S, Clark JN, Hong CC, et al., 2023, In vivo evaluation of ankle kinematics and tibiotalar joint contact strains using digital volume correlation and 3 T clinical MRI, Clinical Biomechanics, Vol: 107, ISSN: 0268-0033
BACKGROUND: In vivo evaluation of ankle joint biomechanics is key to investigating the effect of injuries on the mechanics of the joint and evaluating the effectiveness of treatments. The objectives of this study were to 1) investigate the kinematics and contact strains of the ankle joint and 2) to investigate the correlation between the tibiotalar joint contact strains and the prevalence of osteochondral lesions of the talus distribution. METHODS: Eight healthy human ankle joints were subjected to compressive load and 3 T MRIs were obtained before and after applying load. The MR images in combination with digital volume correlation enabled non-invasive measurement of ankle joint kinematics and tibiotalar joint contact strains in three dimensions. FINDINGS: The total translation of the calcaneus was smaller (0.48 ± 0.15 mm, p < 0.05) than the distal tibia (0.93 ± 0.16 mm) and the talus (1.03 ± 0.26 mm). These movements can produce compressive and shear joint contact strains (approaching 9%), which can cause development of lesions on joints. 87.5% of peak tensile, compressive, and shear strains in the tibiotalar joint took place in the medial and lateral zones. INTERPRETATION: The findings suggested that ankle bones translate independently from each other, and in some cases in opposite directions. These findings help explain the distribution of osteochondral lesions of the talus which have previously been observed to be in medial and lateral regions of the talar dome in 90% of cases. They also provide a reason for the central region of talar dome being less susceptible to developing osteochondral lesions.
Tavana S, Davis B, Canali I, et al., 2023, A novel tool to quantify in vivo lumbar spine kinematics and 3D intervertebral disc strains using clinical MRI, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 140, Pages: 1-12, ISSN: 1751-6161
Medical imaging modalities that calculate tissue morphology alone cannot provide direct information regarding the mechanical behaviour of load-bearing musculoskeletal organs. Accurate in vivo measurement of spine kinematics and intervertebral disc (IVD) strains can provide important information regarding the mechanical behaviour of the spine, help to investigate the effects of injuries on the mechanics of the spine, and assess the effectiveness of treatments. Additionally, strains can serve as a functional biomechanical marker for detecting normal and pathologic tissues. We hypothesised that combining digital volume correlation (DVC) with 3T clinical MRI can provide direct information regarding the mechanics of the spine. Here, we have developed a novel non-invasive tool for in vivo displacement and strain measurement within the human lumbar spine and we used this tool to calculate lumbar kinematics and IVD strains in six healthy subjects during lumbar extension. The proposed tool enabled spine kinematics and IVD strains to be measured with errors that did not exceed 0.17 mm and 0.5%, respectively. The findings of the kinematics study identified that during extension the lumbar spine of healthy subjects experiences total 3D translations ranging from 1 mm to 4.5 mm for different vertebral levels. The findings of strain analysis identified that the average of the maximum tensile, compressive, and shear strains for different lumbar levels during extension ranged from 3.5% to 7.2%. This tool can provide base-line data that can be used to describe the mechanical environment of healthy lumbar spine, which can help clinicians manage preventative treatments, define patient-specific treatments, and to monitor the effectiveness of surgical and non-surgical interventions.
Wai G, Rusli W, Ghouse S, et al., 2023, Statistical shape modelling of the thoracic spine for the development of pedicle screw insertion guides, Biomechanics and Modeling in Mechanobiology, Vol: 22, Pages: 123-132, ISSN: 1617-7940
Spinal fixation and fusion are surgical procedures undertaken to restore stability in the spine and restrict painful or degenerative motion. Malpositioning of pedicle screws during these procedures can result in major neurological and vascular damage. Patient-specific surgical guides offer clear benefits, reducing malposition rates by up to 25%. However, they suffer from long lead times and the manufacturing process is dependent on third-party specialists. The development of a standard set of surgical guides may eliminate the issues with the manufacturing process. To evaluate the feasibility of this option, a statistical shape model (SSM) was created and used to analyse the morphological variations of the T4–T6 vertebrae in a population of 90 specimens from the Visible Korean Human dataset (50 females and 40 males). The first three principal components, representing 39.7% of the variance within the population, were analysed. The model showed high variability in the transverse process (~ 4 mm) and spinous process (~ 4 mm) and relatively low variation (< 1 mm) in the vertebral lamina. For a Korean population, a standardised set of surgical guides would likely need to align with the lamina where the variance in the population is lower. It is recommended that this standard set of surgical guides should accommodate pedicle screw diameters of 3.5–6 mm and transverse pedicle screw angles of 3.5°–12.4°.
Low L, Masouros S, Newell N, 2023, Compressive and Flexion Stiffnesses of Human Cervical, Thoracic and Lumbar Intervertebral Discs Under High-rate Loading, Pages: 1075-1077, ISSN: 2235-3151
Low L, Spurrier E, Newell N, 2023, Blast Injury to the Spine, Blast Injury Science and Engineering A Guide for Clinicians and Researchers: Second Edition, Pages: 181-191, ISBN: 9783031103544
Combat-related spinal injuries have been reported since the Egyptian era. In more recent conflicts improved medical care, and possibly different wounding mechanisms, has seen an increased incidence of spinal injuries. This chapter presents a survey of the patterns, distribution, and demographics of modern spinal blast injuries, reported in the literature. The data is categorised into mounted and dismounted injuries. As different patterns of injury are observed, it is likely that different mechanisms of injury are involved for these two categories. Understanding the mechanism of spinal blast injuries allows the design of vehicles and seats to be improved in order to minimise the severity of blast to military personnel. Analysing the patterns of spinal injury also provides the possibilities of using injury patterns as markers for more severe injuries.
Carpanen D, Newell N, Masouros SD, 2023, Surrogates: Anthropometric Test Devices, Blast Injury Science and Engineering A Guide for Clinicians and Researchers: Second Edition, Pages: 333-341, ISBN: 9783031103544
This chapter presents and discusses the use of physical surrogates for the assessment of human injury. The focus is on anthropomorphic test devices (ATDs), otherwise known as dummies. These have been developed in order to evaluate occupant protection in response to impact loading. They are used extensively in the automotive industry to quantify occupant safety and the defence industry for military vehicle assessment. Their main design objective is to be robust and repeatable. Most ATDs do not assess failure directly; instead, they are heavily instrumented with transducers which record data during testing; these data are then analysed to determine the injury risk in the human.
Masouros SD, Rebelo E, Newell N, 2023, Tertiary Blast Injury and its Protection, Blast Injury Science and Engineering A Guide for Clinicians and Researchers: Second Edition, Pages: 353-355, ISBN: 9783031103544
Tertiary blast injury results from the interaction of the body with solid structures due to bodily or structural displacement caused by blast. This chapter presents briefly the types of tertiary blast, the epidemiology of tertiary blast injury and key advancements in protecting against it.
Rahman T, Baxan N, Murray R, et al., 2022, An in vitro comparison of three nucleus pulposus removal techniques for partial intervertebral disc replacement: An ultra-high resolution MRI study, JOR Spine, ISSN: 2572-1143
Sanz-Pena I, Arachchi S, Curtis-Woodcock N, et al., 2022, Obtaining patient torso geometry for the design of scoliosis braces. A study of the accuracy and repeatability of handheld 3D scanners, Prosthetics and Orthotics International, Vol: 46, Pages: e374-e382, ISSN: 0309-3646
Objective: Obtaining patient geometry is crucial in scoliosis brace design for patients with adolescent idiopathic scoliosis. Advances in 3D scanning technologies provide the opportunity to obtain patient geometries quickly with fewer resources during the design process compared with the plaster-cast method. This study assesses the accuracy and repeatability of such technologies for this application.Methods: The accuracy and repeatability of three different handheld scanners and phone-photogrammetry was assessed using different mesh generation software. Twenty-four scans of a single subject's torso were analyzed for accuracy and repeatability based on anatomical landmark distances and surface deviation maps.Results: Mark II and Structure ST01 scanners showed maximum mean surface deviations of 1.74 ± 3.63 mm and 1.64 ± 3.06 mm, respectively. Deviations were lower for the Peel 1 scanner (maximum of −0.35 ± 2.8 mm) but higher with the use of phone-photogrammetry (maximum of −5.1 ± 4.8 mm). The mean absolute errors of anatomical landmark distance measurements from torso meshes obtained with the Peel 1, Mark II, and ST01 scanners were all within 9.3 mm (3.6%), whereas phone-photogrammetry errors were as high as 18 mm (7%).Conclusions: Low-cost Mark II and ST01 scanners are recommended for obtaining torso geometries because of their accuracy and repeatability. Subject’s breathing/movement affects the resultant geometry around the abdominal and anterolateral regions.
Low L, Salzar R, Newell N, et al., 2022, The Role of Non-linear Stiffness in Modelling High-Rate Axial Loading of the Spine, Pages: 650-651
Caldeira J, Celiz A, Newell N, 2022, A biomechanical testing method to assess tissue adhesives for annulus closure, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 129, Pages: 105150-105150, ISSN: 1751-6161
Intervertebral disc (IVD) degeneration has been linked to Low Back Pain (LBP) which affects over 80% of the population ranking first in terms of disability worldwide. Degeneration progresses with age and is often accompanied by annulus fibrosus (AF) tearing and nucleus pulposus (NP) herniation. Existing therapies fail to restore IVD function and may worsen AF defects, increasing the risk of reherniation in nearly 30% of patients. Current AF closure options are ineffective, presenting biological or mechanical limitations. Bioadhesives have potential use in this area, however methods to assess performance are limited. Herein, we propose a biomechanical testing method to assess bioadhesives’ capacity to seal AF tears.Two candidate bioadhesives to seal AF tears were evaluated; a tough hydrogel adhesive, and a cyanoacrylate-based glue. The adhesion energy at the interface between bovine discs and the tough hydrogel adhesive was quantified using a peel test (n=4). An experimental method to measure the burst pressure of IVDs was then developed. This method was used to quantify the burst pressure of intact (n=7), injured (AF punctured with a 21G needle; n=7), and sealed IVDs (after applying either the tough hydrogel adhesive patch as a sealant; n=5, or the cyanoacrylate-based glue over the AF tear; n=6).The tough adhesive yielded a strong adhesion energy of 239 ± 49 J/m2 during the peel tests. A maximum pressure of 13.2 ± 3.8 MPa was observed for intact discs in the burst pressure tests, which reduced by 61.4% to 5.1 ± 1.5 MPa in the injured IVDs (p < 0.01)). Application of a cyanoacrylate-based glue to injured IVDs did not recover the burst pressure with statistical significance, however, application of the tough adhesive to injured IVDs, restored burst pressure to 12.3 ± 4.5 MPa, which was not significantly different to the intact burst pressures.In this study, a simple biomechanical method to assess the performance of bioadhesives to
Low L, Newell N, Masouros S, 2022, A Multibody Model of the Spine for Injury Prediction in High-Rate Vertical Loading, Pages: 452-460, ISSN: 2235-3151
Underbody blast (UBB) results in lumbar spine injuries in 35% of military-vehicle casualties, resulting in disability and reduced quality of life. A multibody model of a lab-simulated UBB on a full-body cadaver was developed using geometric and inertial properties acquired from a CT scan of the same cadaver. The model comprises a skull, individual vertebral bodies, and a sacrum. Vertebral levels were connected by spring-dampers. Stiffness and damping values were taken from literature of the intervertebral disc and optimized to calibrate the model. The sacrum acceleration recorded in the experiment was input to the model sacrum, and the optimization algorithm worked to maximize the CORA (ISO18571) score of the head and T1 vertebra axial acceleration. The peak accelerations at T1 in the experiment and optimized model were 128 g and 111 g and the times-to-peak were 13.8 ms and 13.9 ms, respectively. The CORA score of both the head and T1 was 0.645 (fair). Stiffness in flexion increased by two orders of magnitude, while other degrees of freedom were scaled by values <100. This study developed a simple, fast-running, subject-specific model to predict injury across the spine. The vision is to assess the probability of injury of any seat configuration, in any vehicle.
Du Y, Tavana S, Rahman T, et al., 2021, Sensitivity of intervertebral disc finite element models to internal geometric and non-geometric parameters, Frontiers in Bioengineering and Biotechnology, Vol: 9, ISSN: 2296-4185
Finite element models are useful for investigating internal intervertebral disc (IVD) behaviours without using disruptive experimental techniques. Simplified geometries are commonly used to reduce computational time or because internal geometries cannot be acquired from CT scans. This study aimed to 1) investigate the effect of altered geometries both at endplates and the nucleus-anulus boundary on model response, and 2) to investigate model sensitivity to material and geometric inputs, and different modelling approaches (graduated or consistent fibre bundle angles and glued or cohesive interlamellar contact). Six models were developed from 9.4T MRIs of bovine IVDs. Models had two variations of endplate geometry (a simple curved profile from the centre of the disc to the periphery, and precise geometry segmented from MRIs), and three variations of NP-AF boundary (linear, curved, and segmented). Models were subjected to axial compressive loading (to 0.86mm at a strain rate of 0.1/sec) and the effect on stiffness and strain distributions, and the sensitivity to modelling approaches was investigated. The model with the most complex geometry (segmented endplates, curved NP-AF boundary) was 3.1 times stiffer than the model with the simplest geometry (curved endplates, linear NP-AF boundary). Peak strains were close to the endplates at locations of high curvature in the segmented endplate models which were not captured in the curved endplate models. Differences were also seen in sensitivity to material properties, graduated fibre angles, cohesive rather than glued interlamellar contact, and NP:AF ratios. These results show that FE modellers must take care to ensure geometries are realistic so that load is distributed and passes through IVDs accurately.
Sanz-Pena I, Arachchi S, Halwala-Vithanage D, et al., 2021, Characterising the mould rectification process for designing scoliosis braces: towards automated digital design of 3D-printed braces, Applied Sciences, Vol: 11, Pages: 1-13, ISSN: 2076-3417
The plaster-casting method to create a scoliosis brace consists of mould generation and rectification to obtain the desired orthosis geometry. Alternative methods entail the use of 3D scanning and CAD/CAM. However, both manual and digital design entirely rely on the orthotist expertise. Characterisation of the rectification process is needed to ensure that digital designs are as efficient as plaster-cast designs. Three-dimensional scans of five patients, pre-, and post-rectification plaster moulds were obtained using a Structure Mark II scanner. Anatomical landmark positions, transverse section centroids, and 3D surface deviation analyses were performed to characterise the rectification process. The rectification process was characterised using two parameters. First, trends in the external contours of the rectified moulds were found, resulting in lateral tilt angles of 81 ± 3.8° and 83.3 ± 2.6° on the convex and concave side, respectively. Second, a rectification ratio at the iliac crest (0.23 ± 0.04 and 0.11 ± 0.02 on the convex and concave side, respectively) was devised, based on the pelvis width to estimate the volume to be removed. This study demonstrates that steps of the manual rectification process can be characterised. Results from this study can be fed into software to perform automatic digital rectification.
Draper D, Newell N, Masouros S, et al., 2021, Multiscale validation of multiple human body model functional spinal units, Journal of Biomechanical Engineering, Vol: 143, ISSN: 0148-0731
A validation comparing five human body model (HBM) lumbar spines is carried out across two load cases, with the objective to use and apply HBMs in high strain rate applications such as car occupant simulation. The first load case consists of an individual intervertebral disc (IVD) loaded in compression at a strain rate of 1/s by a material testing machine. The second load case is a lumbar functional spine unit (FSU) loaded in compression using a drop tower setup, producing strain rates of up to 48/s. The IVD simulations were found to have a better agreement with the experiments than the FSU simulations, and the ranking of which HBMs matched best to the experiment differed by load case. These observations suggest the need for more hierarchical validations of the lumbar spine for increasing the utility of HBMs in high strain rate loading scenarios.
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.
Low L, Salzar R, Newell N, et al., 2021, The Role of Non-linear Stiffness in Modelling High-Rate Axial Loading of the Spine, Pages: 650-651, ISSN: 2235-3151
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Tavana S, Clark J, Newell N, et al., 2020, In vivo deformation and strain measurements in human bone using digital volume correlation (DVC) and 3T clinical MRI, Materials, Vol: 13, ISSN: 1996-1944
Strains within bone play an important role in the remodelling process and the mechanisms of fracture. The ability to assess these strains in vivo can provide clinically relevant information regarding bone health, injury risk, and can also be used to optimise treatments. In vivo bone strains have been investigated using multiple experimental techniques, but none have quantified 3D strains using non-invasive techniques. Digital volume correlation based on clinical MRI (DVC-MRI) is a non-invasive technique that has the potential to achieve this. However, before it can be implemented, uncertainties associated with the measurements must be quantified. Here, DVC-MRI was evaluated to assess its potential to measure in vivo strains in the talus. A zero-strain test (two repeated unloaded scans) was conducted using three MRI sequences, and three DVC approaches to quantify errors and to establish optimal settings. With optimal settings, strains could be measured with a precision of 200 με and accuracy of 480 με for a spatial resolution of 7.5 mm, and a precision of 133 με and accuracy of 251 με for a spatial resolution of 10 mm. These results demonstrate that this technique has the potential to measure relevant levels of in vivo bone strain and to be used for a range of clinical applications.
Newell N, Rivera Tapia D, Rahman T, et al., 2020, Influence of testing environment and loading rate on intervertebral disc compressive mechanics: An assessment of repeatability at three different laboratories, JOR Spine, Vol: 3, Pages: 1-9, ISSN: 2572-1143
In vitro mechanical testing of intervertebral discs is crucial for basic science and pre-clinical testing. Generally, these tests aim to replicate in vivo conditions, but simplifications are necessary in specimen preparation and mechanical testing due to complexities in both structure and the loading conditions required to replicate in vivo conditions. There has been a growing interest in developing a consensus of testing protocols within the spine community to improve comparison of results between studies. The objective of this study was to perform axial compression experiments on bovine bone-disc-bone specimens at three institutions. No differences were observed between testing environment being air, with PBS soaked gauze, or a PBS bath (P > .206). A 100-fold increase in loading rate resulted in a small (2%) but significant increase in compressive mechanics (P < .017). A 7% difference in compressive stiffness between Labs B and C was eliminated when values were adjusted for test system compliance. Specimens tested at Lab A, however, were found to be stiffer than specimens from Lab B and C. Even after normalizing for disc geometry and adjusting for system compliance, an ∼35% difference was observed between UK based labs (B and C) and the USA based lab (A). Large differences in specimen stiffness may be due to genetic differences between breeds or in agricultural feed and use of growth hormones; highlighting significant challenges in comparing mechanics data across studies. This research provides a standardized test protocol for the comparison of spinal specimens and provides steps towards understanding how location and test set-up may affect biomechanical results.
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.
Pearce AP, Marsden M, Newell N, et al., 2020, Trends in admission timing and mechanism of injury can be used to improve general surgical trauma training, Annals of the Royal College of Surgeons of England, Vol: 102, Pages: 36-42, ISSN: 0035-8843
INTRODUCTION: The temporal patterns and unit-based distributions of trauma patients requiring surgical intervention are poorly described in the UK. We describe the distribution of trauma patients in the UK and assess whether changes in working patterns could provide greater exposure for operative trauma training. METHODS: We searched the Trauma Audit and Research Network database to identify all patients between 1 January 2014 to 31 December 2016. Operative cases were defined as all patients who underwent laparotomy, thoracotomy or open vascular intervention. We assessed time of arrival, correlations between mechanism of injury and surgery, and the effect of changing shift patterns on exposure to trauma patients by reference to a standard 10-hour shift assuming a dedicated trauma rotation or fellowship. RESULTS: There were 159,719 patients from 194 hospitals submitted to the Network between 2014 and 2016. The busiest 20 centres accounted for 57,568 (36.0%) of cases in total. Of these 2147/57,568 patients (3.7%) required a general surgical operation; 43% of penetrating admissions (925 cases) and 2.2% of blunt admissions (1222 cases). The number of operations correlated more closely with the number of penetrating rather than blunt admissions (r = 0.89 vs r = 0.51). A diurnal pattern in trauma admissions enabled significant increases in trauma exposure with later start times. CONCLUSIONS: Centres with high volume and high penetrating rates are likely to require more general surgical input and should be identified as locations for operative trauma training. It is possible to improve the number of trauma patients seen in a shift by optimising shift start time.
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
Soltani S, Nogaro MC, Rougelot C, et al., 2019, Spontaneous spinal epidural haematomas in children, EUROPEAN SPINE JOURNAL, Vol: 28, Pages: 2229-2236, ISSN: 0940-6719
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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 T-T, Pearce AP, Carpanen D, et al., 2019, Experimental platforms to study blast injury, Journal of the Royal Army Medical Corps, Vol: 165, Pages: 33-37, ISSN: 2052-0468
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.
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