Search

Whole-body vibration (WBV) is prevalent in labour-related activities and can have adverse effects on the health and performance of the individuals exposed. However, evidence regarding the extent to which human functionality is affected following occupational WBV exposure has not been collated. The current systematic review sought to synthesize existing literature and assess the strength and direction of evidence regarding the acute after-effects of occupational WBV exposure on cognition, visual function, postural stability, and motor control. We conducted a comprehensive search of AMED, CINAHL, MEDLINE, PubMED, Psychology and Behavioural Sciences Collection, SPORTDiscus, APA PsychInfo, Cochrane Library, EMBASE, HMIC, Global Health, ProQuest Central, Scopus, Web of Science, and the US National Technical Information Service on April 26, 2023. Studies that quantified vibration exposure and measured acute changes in cognition, visual function, postural stability, and motor control from baseline to post-vibration were considered without date restriction. Out of the 2663 studies identified, 32 were eligible for inclusion. Based on the Risk of Bias in Non-Randomized Studies of Exposure (ROBINS-E) tool, the studies demonstrated low (66%), moderate (25%) and high risk of bias (9%). The findings indicate that after exposure to WBV, postural stability either deteriorates or remains unchanged. Inconsistent effects of WBV on cognition were reported, while visual function and motor control showed no pronounced changes following WBV. This might be attributed to assessment limitations such as learning effects in neuropsychological and motor tasks, and non-functional measures of vision employed. There was a lack of consistency in the characterization of vibration exposure and the assessment of associated effects on functional performance. Current evidence is therefore insufficient to provide definitive guidance for updating occupational health and safety regulations regarding WBV. However, this review highlights the potential for WBV to jeopardize post-exposure human performance and, consequently, safety. The completion of the review was supported by a UKRI EPSRC training grant. The review has been registered on PROSPERO (ref CRD42023391075)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Intervertebral disc (IVD) degeneration includes changes in tissue biomechanics, physical attributes, biochemical composition, disc microstructure, and cellularity, which can all affect the normal function of the IVD, and ultimately may lead to pain. The purpose of this research was to develop an in-vitro model of degeneration that includes the evaluation of physical, biomechanical, and structural parameters, and that does so over several load/recovery periods. Hyperphysiological loading was used as the degenerative initiator with three experimental groups employed using bovine coccygeal IVD specimens: Control; Single-Overload; and Double-Overload. An equilibrium stage comprising a static load followed by two load/recovery periods was followed by six further load/recovery periods. In the Control group all load/recovery periods were the same, comprising physiological cyclic loading. The overload groups differed in that hyperphysiological loading was applied during the 4th loading period (Single-Overload), or the 4th and 5th loading period (Double-Overload). Overloading led to a significant reduction in disc height compared to the Control group, which was not recovered in subsequent physiological load/recovery periods. However, there were no significant changes in stiffness. Overloading also led to significantly more microstructural damage compared to the Control group. Taking all outcome measures into account, the overload groups were evaluated as replicating clinically relevant aspects of moderate IVD degeneration. Further research into a potential dose-effect, and how more severe degeneration can be replicated would provide a model with the potential to evaluate new treatments and interventions for different stages of IVD degeneration., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Lifestyle heavily influences intervertebral disc (IVD) loads, but measuring in vivo loads requires invasive methods, and the ability to apply these loads in vitro is limited. In vivo load data from instrumented vertebral body replacements is limited to patients that have had spinal fusion surgery, potentially resulting in different kinematics and loading patterns compared to a healthy population. Therefore, this study aimed to develop a pipeline for the non-invasive estimation of in vivo IVD loading, and the application of these loads in vitro. A full-body Opensim model was developed by adapting and combining two existing models. Kinetic data from healthy participants performing activities of daily living were used as inputs for simulations using static optimisation. After evaluating simulation results using in vivo data, the estimated six-axis physiological loads were applied to bovine tail specimens. The pipeline was then used to compare the kinematics resulting from the physiological load profiles (flexion, lateral bending, axial rotation) with a simplified pure moment protocol commonly used for in vitro studies. Comparing kinematics revealed that the in vitro physiological load protocol followed the same trends as the in silico and in vivo data. Furthermore, the physiological loads resulted in substantially different kinematics when compared to pure moment testing, particularly in flexion. Therefore, the use of the presented pipeline to estimate the complex loads of daily activities in different populations, and the application of those loads in vitro provides a novel capability to deepen our knowledge of spine biomechanics, IVD mechanobiology, and improve pre-clinical test methods., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Current spinal testing protocols generally adopt pure moments combined with axial compression. However, daily activities involve multi-axis loads, and multi-axis loading has been shown to impact intervertebral disc (IVD) cell viability. Therefore, integrating in-vivo load data with spine simulators is critical to understand how loading affects the IVD, but doing so is challenging due to load coupling and variable load rates. This study addresses these challenges through the Load Informed Kinematic Evaluation (LIKE) protocol, which was evaluated using the root mean squared error (RMSE) between desired and actual loads in each axis. Stage 1 involves obtaining the kinematics from six-axis load control tests replicating 20 Orthoload activities at a reduced test speed. Stage 2 applies these kinematics in five axes, with axial compression applied in load control, at the reduced speed and at the physiological test rate. Stage 3 enables long-term tests through six-axis kinematic control combined with diurnal height correction to account for the natural height fluctuations of the IVD. Stage 1 yielded RMSEs within twice the load cell noise floor. Low RMSEs were maintained during stage 2 at reduced speed (Tx:0.80 ± 0.30 N; Ty:0.77 ± 0.29 N; Tz:1.79 ± 0.50 N; Rx:0.02 ± 0.01Nm; Ry:0.02 ± 0.01Nm; and Rz:0.02 ± 0.01Nm) and at the physiological test rate (Tx:3.45 ± 1.81 N; Ty:3.82 ± 1.99 N; Tz:11.32 ± 8.69 N; Rx:0.13 ± 0.07Nm; Ry:0.16 ± 0.11Nm; and Rz:0.07 ± 0.04Nm). To address unwanted oscillations observed in longer tests (>2h), Stage 3 was introduced to enable the stable and consistent replication of activities at a physiological test rate. Despite higher RMSEs the axial error was 85.5 ± 24.27 N (equivalent to ∼ 0.16 MPa), with shear RMSEs similar to other testing systems conducting pure moment tests at slower rates. The LIKE protocol enables the replication of physiological loads, providing opportunities for enhanced investigations of IVD mechanobiology, and the pre-clinical evaluation of IVD devices and therapies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Low back pain is the leading cause of disability, producing a substantial socio-economic burden on healthcare systems worldwide. Intervertebral disc (IVD) degeneration is a primary cause of lower back pain, and while regenerative therapies aimed at full functional recovery of the disc have been developed in recent years, no commercially available, approved devices or therapies for the regeneration of the IVD currently exist. In the development of these new approaches, numerous models for mechanical stimulation and preclinical assessment, including in vitro cell studies using microfluidics, ex vivo organ studies coupled with bioreactors and mechanical testing rigs, and in vivo testing in a variety of large and small animals, have emerged. These approaches have provided different capabilities, certainly improving the preclinical evaluation of these regenerative therapies, but challenges within the research environment, and compromises relating to non-representative mechanical stimulation and unrealistic test conditions, remain to be resolved. In this review, insights into the ideal characteristics of a disc model for the testing of IVD regenerative approaches are first assessed. Key learnings from in vivo , ex vivo , and in vitro IVD models under mechanical loading stimulation to date are presented alongside the merits and limitations of each model based on the physiological resemblance to the human IVD environment (biological and mechanical) as well as the possible feedback and output measurements for each approach. When moving from simplified in vitro models to ex vivo and in vivo approaches, the complexity increases resulting in less controllable models but providing a better representation of the physiological environment. Although cost, time, and ethical constraints are dependent on each approach, they escalate with the model complexity. These constraints are discussed and weighted as part of the characteristics of each model., Competing Interests: The authors have no conflicts to disclose., (© 2023 Author(s).)

The intervertebral disc (IVD) provides flexibility, acts as a shock absorber, and transmits load. Degeneration of the IVD includes alterations in the biomechanics, extracellular matrix (ECM), and cellular activity. These changes are not always perceived, however, IVD degeneration can lead to severe health problems including long-term disability. To understand the pathogenesis of IVD degeneration and suitable testing methods for emerging treatments and therapies, this review documents in-vitro models of IVD degeneration including physical disruption, hyperphysiological loading, ECM degradation by enzyme digestion, or a combination of these methods. This paper reviews and critically analyses the models of degeneration published since the year 2000 in either in human or animal specimens. The results are categorised in terms of the IVD biomechanics, physical attributes, ECM composition, tissue damage and cellularity to evaluate the models with respect to natural human degeneration, and to provide recommendations for clinically relevant models for the various stages of degeneration. There is no one model that replicates the wide range of degenerative changes that occur as part of normal degeneration. However, cyclic overloading replicates many aspects of degeneration, with the advantage of a dose-response allowing the tuning of damage initiated. Models of severe degeneration are currently lacking, but there is potential that combining cyclic overloading and enzymatic digestion will provide model that closely resembles human IVD degeneration. This will provide an effective way to investigate the effects of severe degeneration, and the evaluation of treatments for the IVD, which would generally be indicated at this advanced stage of degeneration., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Exposure to whole-body vibration (WBV) increases the risk of low back pain, spinal degeneration, and injury. Cycling can expose participants to WBV, but there are limited data available. This preliminary study quantified WBV in road cyclists in accordance with ISO 2631-1, and determined the efficacy of two seatposts designed to minimise vibration, compared to an aluminium alloy seatpost. Sensors were used to measure the root-mean-squared acceleration (a rms ), frequency-weighted a rms based on an eight-hour reference period (A(8)), vibration dose value (VDV), and transmissibility. Exposures were also calculated using the root-sum-of-squares of the frequency-weighted a rms in all three axes (A(8) rss and VDV rss ). The mean±95% confidence interval A(8) rss and VDV rss across all tests was 0.58 ± 0.07 ms -2 and 37.19 ± 4.70 ms -1.75 respectively at the saddle, if and 0.49 ± 0.06 ms -2 and 24.31 ± 2.89 ms -1.75 respectively at the lumbar position. Occupational limits were exceeded with all seatposts, and there were no significant differences between them (p > 0.227). Road cycling results in substantial WBV, and there was no evidence that the seatposts designed to minimise vibrations successfully do so. Further research into the effect of cycling conditions and equipment on WBV would be valuable to both the research and cycling communities.

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., Competing Interests: The authors have no conflicts of interest to declare., (© 2020 The Authors. JOR Spine published by Wiley Periodicals LLC. on behalf of Orthopaedic Research Society.)

Occupational whole-body vibration (WBV) increases the risk of developing low back and neck pain; yet, there has also been an increased use of therapeutic WBV in recent years. Although the resonant frequency (fr) of the spine decreases as the exposure acceleration increases, effects of varying the vibration profile, including peak-to-peak displacement (sptp), root-mean-squared acceleration (arms), and frequency (f), on pain onset are not known. An established in vivo rat model of WBV was used to characterize the resonance of the spine using sinusoidal sweeps. The relationship between arms and fr was defined and implemented to assess behavioral sensitivity-a proxy for pain. Five groups were subjected to a single 30-min exposure, each with a different vibration profile, and a sham group underwent only anesthesia exposure. The behavioral sensitivity was assessed at baseline and for 7 days following WBV-exposure. Only WBV at 8 Hz induced behavioral sensitivity, and the higher arms exposure at 8 Hz led to a more robust pain response. These results suggest that the development of pain is frequency-dependent, but further research into the mechanisms leading to pain is warranted to fully understand which WBV profiles may be detrimental or beneficial., (Copyright © 2020 by ASME.)

Head collisions in sport can result in catastrophic injuries to the cervical spine. Musculoskeletal modelling can help analyse the relationship between motion, external forces and internal loads that lead to injury. However, impact specific musculoskeletal models are lacking as current viscoelastic values used to describe cervical spine joint dynamics have been obtained from unrepresentative quasi-static or static experiments. The aim of this study was to develop and validate a cervical spine musculoskeletal model for use in axial impacts. Cervical spine specimens (C2-C6) were tested under measured sub-catastrophic loads and the resulting 3D motion of the vertebrae was measured. Specimen specific musculoskeletal models were then created and used to estimate the axial and shear viscoelastic (stiffness and damping) properties of the joints through an optimisation algorithm that minimised tracking errors between measured and simulated kinematics. A five-fold cross validation and a Monte Carlo sensitivity analysis were conducted to assess the performance of the newly estimated parameters. The impact-specific parameters were integrated in a population specific musculoskeletal model and used to assess cervical spine loads measured from Rugby union impacts compared to available models. Results of the optimisation showed a larger increase of axial joint stiffness compared to axial damping and shear viscoelastic parameters for all models. The sensitivity analysis revealed that lower values of axial stiffness and shear damping reduced the models performance considerably compared to other degrees of freedom. The impact-specific parameters integrated in the population specific model estimated more appropriate joint displacements for axial head impacts compared to available models and are therefore more suited for injury mechanism analysis., Competing Interests: The authors have declared that no competing interests exist.

The complexity of multi-axis spine testing often makes it challenging to compare results from different studies. The aim of this work was to develop and implement a standardized testing protocol across three six-axis spine systems, compare them, and provide stiffness and phase angle limits against which other test systems can be compared. Standardized synthetic lumbar specimens (n=5), comprising three springs embedded in polymer at each end, were tested on each system using pure moments in flexion-extension, lateral bending, and axial rotation. Tests were performed using sine and triangle waves with an amplitude of 8Nm, a frequency of 0.1Hz, and with axial preloads of 0 and 500N. The stiffness, phase angle, and R 2 value of the moment against rotation in the principal axis were calculated at the center of each specimen. The tracking error was adopted asa measure of each test system to minimize non-principal loads, defined as the root mean squared difference between actual and target loads. All three test systems demonstrated similar stiffnesses, with small (<14%) but significant differences in 4 of 12 tests. More variability was observed in the phase angle between the principal axis moment and rotation, with significant differences in 10 of 12 tests. Stiffness and phase angle limits were calculated based on the 95% confidence intervals from all three systems. These recommendations can be used with the standard specimen and testing protocol by other research institutions to ensure equivalence of different spine systems, increasing the ability to compare in vitro spine studies., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Total hip replacement is aimed at relieving pain and restoring function. Currently, imaging techniques are primarily used as a clinical diagnosis and follow-up method. However, these are unreliable for detecting early loosening, and this has led to the proposal of novel techniques such as vibrometry. The present study had two aims, namely, the validation of the outcomes of a previous work related to loosening detection, and the provision of a more realistic anatomical representation of the clinical scenario. The acetabular cup loosening conditions (secure, and 1 and 2 mm spherical loosening) considered were simulated using Sawbones composite bones. The excitation signal was introduced in the femoral lateral condyle region using a frequency range of 100-1500 Hz. Both the 1 and 2 mm spherical loosening conditions were successfully distinguished from the secure condition, with a favourable frequency range of 500-1500 Hz. The results of this study represent a key advance on previous research into vibrometric detection of acetabular loosening using geometrically realistic model, and demonstrate the clinical potential of this technique., (Crown Copyright © 2017. Published by Elsevier Ltd. All rights reserved.)

Synopsis Chronic neck pain is a common condition and a primary clinical symptom of whiplash and other spinal injuries. Loading-induced neck injuries produce abnormal kinematics between the vertebrae, with the potential to injure facet joints and the afferent fibers that innervate the specific joint tissues, including the capsular ligament. Mechanoreceptive and nociceptive afferents that innervate the facet have their peripheral terminals in the capsule, cell bodies in the dorsal root ganglia, and terminal processes in the spinal cord. As such, biomechanical loading of these afferents can initiate nociceptive signaling in the peripheral and central nervous systems. Their activation depends on the local mechanical environment of the joint and encodes the neural processes that initiate pain and lead to its persistence. This commentary reviews the complex anatomical, biomechanical, and physiological consequences of facet-mediated whiplash injury and pain. The clinical presentation of facet-mediated pain is complex in its sensory and emotional components. Yet, human studies are limited in their ability to elucidate the physiological mechanisms by which abnormal facet loading leads to pain. Over the past decade, however, in vivo models of cervical facet injury that reproduce clinical pain symptoms have been developed and used to define the complicated and multifaceted electrophysiological, inflammatory, and nociceptive signaling cascades that are involved in the pathophysiology of whiplash facet pain. Integrating the whiplash-like mechanics in vivo and in vitro allows transmission of pathophysiological mechanisms across scales, with the hope of informing clinical management. Yet, despite these advances, many challenges remain. This commentary further describes and highlights such challenges. J Orthop Sports Phys Ther 2017;47(7):450-461. Epub 16 Jun 2017. doi:10.2519/jospt.2017.7255.

Objectives: Fractures of the proximal femur are a common clinical problem, and a number of orthopaedic devices are available for the treatment of such fractures. The objective of this study was to assess the rotational stability, a common failure predictor, of three different rotational control design philosophies: a screw, a helical blade and a deployable crucifix., Methods: Devices were compared in terms of the mechanical work (W) required to rotate the implant by 6° in a bone substitute material. The substitute material used was Sawbones polyurethane foam of three different densities (0.08 g/cm 3 , 0.16 g/cm 3 and 0.24 g/cm 3 ). Each torsion test comprised a steady ramp of 1°/minute up to an angular displacement of 10°., Results: The deployable crucifix design (X-Bolt), was more torsionally stable, compared to both the dynamic hip screw (DHS, p = 0.008) and helical blade (DHS Blade, p= 0.008) designs in bone substitute material representative of osteoporotic bone (0.16 g/cm 3 polyurethane foam). In 0.08 g/cm 3 density substrate, the crucifix design (X-Bolt) had a higher resistance to torsion than the screw (DHS, p = 0.008). There were no significant differences (p = 0.101) between the implants in 0.24 g/cm 3 density bone substitute., Conclusions: Our findings indicate that the clinical standard proximal fracture fixator design, the screw (DHS), was the least effective at resisting torsional load, and a novel crucifix design (X-Bolt), was the most effective design in resisting torsional load in bone substitute material with density representative of osteoporotic bone. At other densities the torsional stability was also higher for the X-Bolt, although not consistently significant by statistical analysis. Cite this article : J. D. Gosiewski, T. P. Holsgrove, H. S. Gill. The efficacy of rotational control designs in promoting torsional stability of hip fracture fixation. Bone Joint Res 2017;6:270-276. DOI: 10.1302/2046-3758.65.BJR-2017-0287.R1., Competing Interests: ICMJE COI Statement: Professor Gill is a member of the Editorial Board of The Bone & Joint Journal, and a member of Executive Committees of the British and European Orthopaedic Research Societies., (© 2017 Gosiewski et al.)

In-vitro testing protocols used for spine studies should replicate the in-vivo load environment as closely as possible. Unconstrained moments are regularly employed to test spinal specimens in-vitro, but applying such loads dynamically using an active six-axis testing system remains a challenge. The aim of this study was to assess the capability of a custom-developed spine simulator to apply dynamic unconstrained moments with an axial preload. Flexion-extension, lateral bending, and axial rotation were applied to an L5/L6 porcine specimen at 0.1 and 0.3Hz. Non-principal moments and shear forces were minimized using load control. A 500N axial load was applied prior to tests, and held stationary during testing to assess the effect of rotational motion on axial load. Non-principal loads were minimized to within the load cell noise-floor at 0.1Hz, and within two-times the load-cell noise-floor in all but two cases at 0.3Hz. The adoption of position control in axial compression-extension resulted in axial loads with qualitative similarities to in-vivo data. This study successfully applied dynamic, unconstrained moments with a physiological preload using a six-axis control system. Future studies will investigate the application of dynamic load vectors, multi-segment specimens, and assess the effect of injury and degeneration., (Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.)

Cervical spine trauma from sport or traffic collisions can have devastating consequences for individuals and a high societal cost. The precise mechanisms of such injuries are still unknown as investigation is hampered by the difficulty in experimentally replicating the conditions under which these injuries occur. We harness the benefits of computer simulation to report on the creation and validation of i) a generic musculoskeletal model (MASI) for the analyses of cervical spine loading in healthy subjects, and ii) a population-specific version of the model (Rugby Model), for investigating cervical spine injury mechanisms during rugby activities. The musculoskeletal models were created in OpenSim, and validated against in vivo data of a healthy subject and a rugby player performing neck and upper limb movements. The novel aspects of the Rugby Model comprise i) population-specific inertial properties and muscle parameters representing rugby forward players, and ii) a custom scapula-clavicular joint that allows the application of multiple external loads. We confirm the utility of the developed generic and population-specific models via verification steps and validation of kinematics, joint moments and neuromuscular activations during rugby scrummaging and neck functional movements, which achieve results comparable with in vivo and in vitro data. The Rugby Model was validated and used for the first time to provide insight into anatomical loading and cervical spine injury mechanisms related to rugby, whilst the MASI introduces a new computational tool to allow investigation of spinal injuries arising from other sporting activities, transport, and ergonomic applications. The models used in this study are freely available at simtk.org and allow to integrate in silico analyses with experimental approaches in injury prevention., Competing Interests: The authors have declared that no competing interests exist.

Dynamic cervical spine loading can produce facet capsule injury. Despite a large proportion of neck pain being attributable to the C2/C3 facet capsule, potential mechanisms are not understood. This study replicated low-speed frontal and rear-end traffic collisions in occiput-C3 human cadaveric cervical spine specimens and used kinematic and full-field strain analyses to assess injury. Specimens were loaded quasi-statically in flexion and extension before and after dynamic rotation of C3 at 100 deg/s. Global kinematics in the sagittal plane were tracked at 1 kHz, and C2/C3 facet capsule full-field strains were measured. Dynamic loading did not alter the kinematics from those during quasi-static (QS) loading, but maximum principal strain (MPS) and shear strain (SS) were significantly higher (p = 0.028) in dynamic flexion than for the same quasi-static conditions. The full-field strain analysis demonstrated that capsule strain was inhomogeneous, and that the peak MPS generally occurred in the anterior aspect and along the line of the C2/C3 facet joint. The strain magnitude in dynamic flexion continued to rise after the rotation of C3 had stopped, with a peak MPS of 12.52 ± 4.59% and a maximum SS of 5.34 ± 1.60%. The peak MPS in loading representative of rear-end collisions approached magnitudes previously shown to induce pain in vivo, whereas strain analysis using linear approaches across the facet joint was lower and may underestimate injury risk compared to full-field analysis. The time at which peak MPS occurred suggests that the deceleration following a collision is critical in relation to the production of injurious strains within the facet capsule.

Biomechanical studies of rugby union scrummaging have focused on kinetic and kinematic analyses, while muscle activation strategies employed by front-row players during scrummaging are still unknown. The aim of the current study was to investigate the activity of spinal muscles during machine and live scrums. Nine male front-row forwards scrummaged as individuals against a scrum machine under "crouch-touch-set" and "crouch-bind-set" conditions, and against a two-player opposition in a simulated live condition. Muscle activities of the sternocleidomastoid, upper trapezius, and erector spinae were measured over the pre-engagement, engagement, and sustained-push phases. The "crouch-bind-set" condition increased muscle activity of the upper trapezius and sternocleidomastoid before and during the engagement phase in machine scrummaging. During the sustained-push phase, live scrummaging generated higher activities of the erector spinae than either machine conditions. These results suggest that the pre-bind, prior to engagement, may effectively prepare the cervical spine by stiffening joints before the impact phase. Additionally, machine scrummaging does not replicate the muscular demands of live scrummaging for the erector spinae, and for this reason, we advise rugby union forwards to ensure scrummaging is practiced in live situations to improve the specificity of their neuromuscular activation strategies in relation to resisting external loads., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Thorough pre-testing is critical in assessing the likely in vivo performance of spinal devices prior to clinical use. However, there is a lack of data available concerning the dynamic testing of lumbar (porcine model) total disc replacements in all six axes under preload conditions. The aim of this study was to provide new data comparing porcine lumbar spinal specimen stiffness between the intact state and after the implantation of an unconstrained total disc replacement, in 6 degrees of freedom. The dynamic, stiffness matrix testing of six porcine lumbar isolated disc specimens was completed using triangle waves at a test frequency of 0.1 Hz. An axial preload of 500 N was applied during all testing. Specimens were tested both in the intact condition and after the implantation of the total disc replacement. Sixteen key stiffness terms were identified for the comparison of the intact and total disc replacement specimens, comprising the 6 principal stiffness terms and 10 key off-axis stiffness terms. The total disc replacement specimens were significantly different to the intact specimens in 12 of these key terms including all six principal stiffness terms. The implantation of the total disc replacement resulted in a mean reduction in the principal stiffness terms of 100%, 91%, and 98% in lateral bending, flexion-extension, and axial rotation, respectively. The novel findings of this study have demonstrated that the unconstrained, low-friction total disc replacement does not replicate the stiffness of the intact specimens. It is likely that other low-friction total disc replacements would produce similar results due to stiffness being actively minimised as part of the design of low-friction devices, without the introduction of stiffening elements or mechanisms to more accurately replicate the mechanical properties of the natural intervertebral disc. This study has demonstrated, for the first time, a method for the quantitative comparative mechanical function testing of total disc replacements and provides baseline data for the development of future devices., (© IMechE 2015.)

Background Context: High-energy impacts are commonly encountered during sports such as rugby union. Although catastrophic injuries resulting from such impacts are rare, the consequences can be devastating for all those involved. A greater level of understanding of cervical spine injury mechanisms is required, with the ultimate aim of minimizing such injuries., Purpose: The present study aimed to provide a greater understanding of cervical spine injury mechanisms, by subjecting porcine spinal specimens to impact conditions based on those measured in vivo. The impacts were investigated using high-speed digital image correlation (DIC), a method not previously adopted for spinal impact research., Study Design: This was an in vitro biomechanical study., Methods: Eight porcine specimens were impacted using a custom-made rig. The cranial and caudal axial loads were measured at 1 MHz. Video data were captured with two cameras at 4 kHz, providing measurements of the three-dimensional deformation and surface strain field of the specimens using DIC., Results: The injuries induced on the specimens were similar to those observed clinically. The mean±standard deviation peak caudal load was 6.0±2.1 kN, which occurred 5.6±1.1 ms after impact. Damage observable with the video data occurred in six specimens, 5.4±1.1 ms after impact, and the peak surface strain at fracture initiation was 4.6±0.5%., Conclusions: This study has provided an unprecedented insight into the injury mechanisms of the cervical spine during impact loading. The posture represents a key factor in injury initiation, with lordosis of the spine increasing the likelihood of injury., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Current techniques for diagnosing early loosening of a total hip replacement (THR) are ineffective, especially for the acetabular component. Accordingly, new, accurate, and quantifiable methods are required. The aim of this study was to investigate the viability of vibrational analysis for accurately detecting acetabular component loosening. A simplified acetabular model was constructed using a Sawbones(®) foam block. By placing a thin silicone layer between the acetabular component and the Sawbones block, 2- and 4-mm soft tissue membranes were simulated representing different loosening scenarios. A constant amplitude sinusoidal excitation with a sweep range of 100-1500 Hz was used. Output vibration from the model was measured using an accelerometer and an ultrasound probe. Loosening was determined from output signal features such as the number and relative strength of observed harmonic frequencies. Both measurement methods were sufficient to measure the output vibration. Vibrational analysis reliably detected loosening corresponding to both 2 and 4 mm tissue membranes at driving frequencies between 100 and 1000 Hz (p < 0.01) using the accelerometer. In contrast, ultrasound detected 2-mm loosening at a frequency range of 850-1050 Hz (p < 0.01) and 4-mm loosening at 500-950 Hz (p < 0.01)., (Copyright © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.)

Back pain and spinal degeneration affect a large proportion of the general population. The economic burden of spinal degeneration is significant, and the treatment of spinal degeneration represents a large proportion of healthcare costs. However, spinal surgery does not always provide improved clinical outcomes compared to non-surgical alternatives, and modern interventions, such as total disc replacement, may not offer clinically relevant improvements over more established procedures. Although psychological and socioeconomic factors play an important role in the development and response to back pain, the variation in clinical success is also related to the complexity of the spine, and the multi-faceted manner by which spinal degeneration often occurs. The successful surgical treatment of degenerative spinal conditions requires collaboration between surgeons, engineers, and scientists in order to provide a multi-disciplinary approach to managing the complete condition. In this review, we provide relevant background from both the clinical and the basic research perspectives, which is synthesized into several examples and recommendations for consideration in increasing translational research between communities with the goal of providing improved knowledge and care. Current clinical imaging, and multi-axis testing machines, offer great promise for future research by combining invivo kinematics and loading with in-vitro testing in six degrees of freedom to offer more accurate predictions of the performance of new spinal instrumentation. Upon synthesis of the literature, it is recommended that in-vitro tests strive to recreate as many aspects of the in-vivo environment as possible, and that a physiological preload is a critical factor in assessing spinal biomechanics in the laboratory. A greater link between surgical procedures, and the outcomes in all three anatomical planes should be considered in both the in-vivo and in-vitro settings, to provide data relevant to quality of motion, and stability.

Creating bi-laminar cement mantles as part of revision hip arthroplasty is well-documented but there is a lack of data concerning the effect of cement brand on the procedure. The aim of this study was to compare the shear strength of bi-laminar cement mantles using various combinations of two leading bone cement brands.Bi-laminar cement mantles were created using Simplex P with Tobramycin, and Palacos R+G: Simplex-Simplex (SS); Simplex-Palacos (SP); Palacos-Simplex (PS); and Palacos-Palacos (PP). Additionally, specimens were produced by rasping (R) the surface of the original mantle, or leaving it unrasped (U), leading to a total of eight groups (n = 10). Specimens were loaded in shear, at 0.1 mm/min, until failure, and the maximum shear strength calculated.The highest mean shear strength was found in the PSU and PSR groups (23.69 and 23.89 MPa respectively), and the lowest in the PPU group (14.70 MPa), which was significantly lower than all but two groups. Unrasped groups generally demonstrated greater standard error than rasped groups.In a further comparison to assess the effect of the new cement mantle brand, irrespective of the brand of the original mantle, Simplex significantly increased the shear strength compared to Palacos with equivalent preparation.It is recommended that the original mantle is rasped prior to injection of new cement, and that Simplex P with Tobramycin be used in preference to Palacos R+G irrespective of the existing cement type. Further research is needed to investigate more cement brands, and understand the underlying mechanisms relating to cement-in-cement procedures.

Background Context: Complex testing protocols are required to fully understand the biomechanics of the spine. There remains limited data concerning the mechanical properties of spinal specimens under dynamic loading conditions in six axes., Purpose: To provide new data on the mechanical properties of functional spinal unit (FSU) and isolated disc (ISD) spinal specimens in 6 df., Study Design: Dynamic, six-axis stiffness matrix testing of porcine lumbar spinal specimens., Methods: The stiffness matrix testing of lumbar porcine FSU (n=6) and ISD (n=6) specimens was completed in a custom six-axis spine simulator using triangle wave cycles at a frequency of 0.1 Hz. Specimens were first tested without an axial preload, then with an axial preload of 500 N, with equilibration times of both 30 and 60 minutes., Results: The stiffness matrices were not symmetrical about the principal stiffness terms. The facets increased all the principal stiffness terms with the exception of axial compression-extension. Significant differences were detected in 15 stiffness terms because of the application of an axial preload in the ISD specimens, including an increase in all principal stiffness terms. There were limited differences in stiffness because of equilibration time of 30 and 60 minutes., Conclusions: The assumption of stiffness matrix symmetry used in many previous studies is not valid. The biomechanical testing of spinal specimens should be completed in 6 df, at physiologic loading rates, and incorporate the application of an axial preload. The present study has provided new data on the mechanical properties of spinal specimens and demonstrates that the dynamic stiffness matrix method provides a means to more fully understand the natural spine and quantitatively assess spinal instrumentation., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background Context: Although a great deal of research has been completed to characterize the stiffness of spinal specimens, there remains a limited understanding of the spine in 6 df and there is a lack of data from dynamic testing in six axes., Purpose: This study details the development and validation of a dynamic six-axis spine simulator., Study Design: Biomechanical study., Methods: A synthetic spinal specimen was used for the purpose of tuning the simulator, completing positional accuracy tests, and measuring frequency response under physiological conditions. The spine simulator was used to complete stiffness matrix tests of an L3-L4 lumbar porcine functional spinal unit. Five testing frequencies were used, ranging from quasistatic (0.00575 Hz) to dynamic (0.5 Hz). Tests were performed without an axial preload and with an axial preload of 500 N., Results: The validation tests demonstrated that the simulator is capable of producing accurate positioning under loading at frequencies up to 0.5 Hz using both sine and triangle waveforms. The porcine stiffness matrix tests demonstrated that the stiffness matrix is not symmetrical about the principal stiffness diagonal. It was also shown that while an increase in test frequency generally increased the principal stiffness terms, axial preload had a much greater effect., Conclusions: The spine simulator is capable of characterizing the dynamic biomechanics of the spine in six axes and provides a means to better understand the complex behavior of the spine under physiological conditions., (Copyright © 2014 Elsevier Inc. All rights reserved.)

When proximal bone stock is compromised at revision hip arthroplasty, distal fixation is often relied upon for stability of the femoral component. In such circumstances, torsional forces can result in debonding and loosening. This study compared the torsional behaviour of a cemented, polished and featureless (plain) stem with cemented, polished stems featuring fins or flutes. The finned stem construct was found to be significantly stiffer than the fluted stem. The maximum torque of the finned and fluted stems was significantly higher than the plain stem, with no difference between the finned and fluted stems. Distal stem features may provide a more reliable and greater resistance to torque in polished, cemented revision hip stems. Finned stem features may also increase the stiffness of the construct.

Impaction bone grafting (IBG) is widely used for revision hip surgery to compensate for bone stock loss. It is performed by impacting morsellized allograft into the femoral canal and acetabulum prior to cementing new total hip components. Per- and post-operative femoral fractures and post-operative implant subsidence are major complications in IBG. The aim of this study was to investigate the strain distribution on the medial side of the femur during impaction grafting and the subsequent stability of the stem under uniaxial cyclic loading. The Exeter IBG technique was used in conjunction with Howmedica X-change instrumentation. Sawbones composite femora were used. An impactometer, which provides a known impaction energy and momentum, was used to standardize the impaction process. Three drop heights, 130, 260, and 390 mm, were used for proximal impaction. In-vitro medial hoop strains and the number of impacts were recorded. A drop height of 260 mm was found to provide sufficient energy for impaction without introducing excessive strains to achieve implant stability. Furthermore, a feasibility study was performed on the use of a proximal impaction cap (PIC) to restrain extrusion of the graft during impaction. Although no significant difference in impaction strains or stem stability in uniaxial cylic loading was found by using a PIC, it is postulated that the design of a proximal impactor could be improved to assist with proximal stem alignment and graft containment.