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Abstract Background Questions regarding the distribution of stress in the proximal human femur have never been adequately resolved. Traditionally, by considering the femur in isolation, it has been believed that the effect of body weight on the projecting neck and head places the superior aspect of the neck in tension. A minority view has proposed that this region is in compression because of muscular forces pulling the femur into the pelvis. Little has been done to study stress distributions in the proximal femur. We hypothesise that under physiological loading the majority of the proximal femur is in compression and that the internal trabecular structure functions as an arch, transferring compressive stresses to the femoral shaft. Methods To demonstrate the principle, we have developed a 2D finite element model of the femur in which body weight, a representation of the pelvis, and ligamentous forces were included. The regions of higher trabecular bone density in the proximal femur (the principal trabecular systems) were assigned a higher modulus than the surrounding trabecular bone. Two-legged and one-legged stances, the latter including an abductor force, were investigated. Results The inclusion of ligamentous forces in two-legged stance generated compressive stresses in the proximal femur. The increased modulus in areas of greater structural density focuses the stresses through the arch-like internal structure. Including an abductor muscle force in simulated one-legged stance also produced compression, but with a different distribution. Conclusion This 2D model shows, in principle, that including ligamentous and muscular forces has the effect of generating compressive stresses across most of the proximal femur. The arch-like trabecular structure transmits the compressive loads to the shaft. The greater strength of bone in compression than in tension is then used to advantage. These results support the hypothesis presented. If correct, a better understanding of the stress distribution in the proximal femur may lead to improvements in prosthetic devices and an appreciation of the effects of various surgical procedures affecting load transmission across the hip.

STUDY DESIGN: Analysis of positional magnetic resonance images of normal volunteers. OBJECTIVE: To compare the reliability and precision of an active shape model to that of conventional lordosis measurements. SUMMARY OF BACKGROUND DATA: Characterization of lumbar lordosis commonly relies on measurement of angles; these have been found to have errors of around 10 degrees . METHODS: T2 weighted sagittal images of the lumbar spines of 24 male volunteers in the standing posture were acquired using a positional magnetic resonance scanner. An active shape model of the vertebral bodies from S1 to L1 was created. Lumbar lordosis was also determined by measuring the angles of the superior endplates. All measurements were performed twice by one observer and once by a second observer. RESULTS: The shape model identified 2 modes of variation to describe the shape of the lumbar spine (mode 1 described curvature and mode 2 described evenness of curvature). Significant correlations were found between mode 1 and total lordosis (R = 0.97, P < 0.001) and between mode 2 and mean absolute deviation of segmental lordosis (R = 0.80, P < 0.001). Intra- and interobserver reliability was higher for the shape model (intraclass correlation coefficients, 0.98-1.00) than for the lordosis angle measurements (intraclass correlation coefficients, 0.68-0.99). The relative error of the shape model (mode 1 = 4%; mode 2 = 9%) was lower than the conventional measurements (total lordosis = 10%). CONCLUSION: The shape of the lumbar spine in the sagittal plane can be comprehensively characterized using a shape model. The results are more reliable and precise than measurements of lordosis calculated from endplate angles. [ABSTRACT FROM AUTHOR]

Background: Experimental results are commonly fitted by determining parameter values of suitable mathematical expressions. In case a relation exists between different data sets, the accuracy of the parameters obtained can be increased by incorporating this relationship in the fitting process instead of fitting the recordings separately. Methods: An algorithm to fit multiple measured curves simultaneously was developed. The method accounts for parameters that are shared by some curves. It can be applied to either linear or nonlinear equations. Simulated noisy "measurement results" were created to compare the introduced method to the "straight forward" way of fitting the curves separately. Results: The analysis of the simulated measurements confirm, that the introduced method yields more accurate parameters compared to the ones gained by fitting the measurements separately. Therefore it needs more computer time. As an example, the new fitting algorithm is applied to the measurements of the evoked compound action potentials (ECAP) of the auditory nerve: This leads to promising ideas to reduce artefacts generated by the measuring process. Conclusion: The introduced fitting algorithm uses the relationship between multiple measurement results to increase the accuracy of the parameters. Its application in the field of ECAP measurements is promising and should be further investigated. [ABSTRACT FROM AUTHOR]

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.)

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.)

The demand for revision knee replacement (RKR) has increased dramatically with rising patient life expectancy and younger recipients for primary TKR. However, significant challenges to RKR arise from osseous defects, reduced bone quality, potential bone volume loss from implant removal and the need to achieve implant stability. This study utilizes the outcomes of an ongoing RKR clinical trial using porous metaphyseal cones 3D-printed of titanium, to investigate 1) bone mineral density (BMD) changes in three fixation zones (epiphysis, metaphysis, and diaphysis) over a year and 2) the biomechanical effects of the cones at 6 months post-surgery. It combines dual-energy x-ray absorptiometry (DXA), computed tomography (CT) with patient-specific based finite element (FE) modelling. Bone loss (-0.086 ± 0.05 g/cm 2 ) was found in most patients over the first year. The biomechanical assessment considered four different loading scenarios from standing, walking on a flat surface, and walking downstairs, to a simulated impact of the knee. The patient-specific FE models showed that the cones marginally improved the strain distribution in the bone and shared the induced load but played a limited role in reducing the risks of bone fracture or cement debonding. This technique of obtaining real live data from a randomized clinical trial and inserting it into an in-silico FE model is unique and innovative in RKR research. The tibia RKR biomechanics examined open up further possibilities, allowing the in-silico testing of prototypes and implant combinations without putting patients at risk as per the recommended IDEAL framework standards. This process with further improvements could allow rapid innovation, optimization of implant design, and improve surgical planning., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The interface between the intervertebral disc and the vertebral body is important to the discs' biomechanics and physiology, and is widely implicated in its pathology. This study aimed to explore biochemically and structurally the bony endplate, cartilage endplate and intervertebral disc, below the nucleus and below the annulus in healthy bovine tails. Multiphoton imaging and spontaneous Raman spectroscopy were employed. Raman spectroscopy provided relative quantification of mineral and matrix components across the vertebral endplate and its adjacent areas with microscopic spatial resolution. Microscopy utilising second-harmonic generation (SHG) and two-photon fluorescence (TPF) allowed for the structural identification of distinct endplate regions. The cartilage endplate was revealed as structurally distinct from both the bone and disc, supporting its biomechanical function as a transition zone between the soft and hard tissue components. The collagen fibres were continuous across the tidemark which defines the interface between the mineralised and non-mineralised regions of the endplate. Raman spectroscopy revealed gradients in phosphate and carbonate content through the depth of the endplate and also differences beneath the nucleus and annulus consistent with a higher rate of remodelling under the annulus.

Needle injection has been widely used in spinal therapeutic or diagnostic processes, such as discography. The use of needles has been suspected in causing mild disc degeneration which can lead to long-term back pain. However, the localised microscopic damage caused by needles has not been well studied. The local progressive damage on a microscopic level caused by needle punctures on the surface of bovine annulus fibrosus was investigated. Four different sizes of needle were used for the puncture and twenty-nine bovine intervertebral discs were studied. Polarization-resolved second harmonic generation and fluorescent microscopy were used to study the local microscopic structural changes in collagen and cell nuclei due to needle damage. Repeated 70 cyclic loadings at ±5% of axial strain were applied after the needle puncture in order to assess progressive damage caused by the needle. Puncture damage on annulus fibrosus were observed either collagen fibre bundles being pushed aside, being cut through or combination of both with part being lift or pushed in. The progressive damage was found less relevant to the needle size and more progressive damage was only observed using the larger needle. Two distinct populations of collagen, in which one was relatively more organised than the other population, were observed especially after the puncture from skewed distribution of polarization-SHG analysis. Cell shape was found rounder near the puncture site where collagen fibres were damaged., (Copyright © 2021. Published by Elsevier Ltd.)

The main function of the intervertebral disc is biomechanical function, since it must resist repetitive high loadings, while giving the spine its flexibility and protecting the spinal cord from over-straining. It partially owes its mechanical characteristics to the lamellar architecture of its outer layer, the annulus fibrosus. Today, no non-invasive means exist to characterize annulus lamellar structure in vivo. The aim of this work was to test the feasibility of imaging annulus fibrosus microstructure in vivo with ultrasonography. Twenty-nine healthy adolescents were included. Ultrasonographies of L3-L4 disc were acquired with a frontal approach. Annulus fibrosus was segmented in the images to measure the thickness of the lamellae. To validate lamellar appearance in ultrasonographies, multimodality images of two cow tail discs were compared: ultrasonography, magnetic resonance and optical microscopy. In vivo average lamellar thickness was 229.7 ± 91.5 μm, and it correlated with patient body mass index and age. Lamellar appearance in the three imaging modalities in vitro was consistent. Lamellar measurement uncertainty was 7%, with good agreement between two operators. Feasibility of ultrasonography for the analysis of lumbar annulus fibrosus structure was confirmed. Further work should aim at validating measurement reliability, and to assess the relevance of the method to characterize annulus alterations, for instance in disc degeneration or scoliosis.

The development of automatic methods for segmenting anatomy from medical images is an important goal for many medical and healthcare research areas. Datasets that can be used to train and test computer algorithms, however, are often small due to the difficulties in obtaining experts to segment enough examples. Citizen science provides a potential solution to this problem but the feasibility of using the public to identify and segment anatomy in a medical image has not been investigated. Our study therefore aimed to explore the feasibility, in terms of performance and motivation, of using citizens for such purposes. Public involvement was woven into the study design and evaluation. Twenty-nine citizens were recruited and, after brief training, asked to segment the spine from a dataset of 150 magnetic resonance images. Participants segmented as many images as they could within three one-hour sessions. Their accuracy was evaluated by comparing them, as individuals and as a combined consensus, to the segmentations of three experts. Questionnaires and a focus group were used to determine the citizens' motivation for taking part and their experience of the study. Citizen segmentation accuracy, in terms of agreement with the expert consensus segmentation, varied considerably between individual citizens. The citizen consensus, however, was close to the expert consensus, indicating that when pooled, citizens may be able to replace or supplement experts for generating large image datasets. Personal interest and a desire to help were the two most common reasons for taking part in the study., Competing Interests: The authors have declared that no competing interests exist.

Study Design: Feasibility study on characterizing thoracic vertebral shape from magnetic resonance images using a shape model., Objectives: Assess the reliability of characterizing thoracic vertebral shape from magnetic resonance images and estimate the normal variation in vertebral shape using a shape model., Summary of Background Data: The characterization of thoracic vertebra shape is important for understanding the initiation and progression of deformity and in developing surgical methods. Methods for characterizing shape need to be comprehensive, reliable, and suitable for use in vivo., Methods: Magnetic resonance images of the thoracic vertebrae were acquired from 20 adults. Repeat scans were acquired, after repositioning the participants, for T4, T8, and T12. Landmark points were placed around the vertebra on the images and used to create a shape model. The reliability was assessed using relative error (E%) and intraclass correlation (ICC). The effect of vertebral level, sex and age on vertebral shape was assessed using repeated measures analysis of variance., Results: Five modes of variation were retained from the shape model. Reliability was excellent for the first two modes (mode 1: E% = 7, ICC = 0.98; mode 2: E% = 11, ICC = 0.96). These modes described variation in the vertebral bodies, the pedicle width and orientation, and the facet joint position and orientation with respect to the pedicle axis. Variation in vertebral shape was found along the thoracic spine and between individuals, but there was little effect of age and sex., Conclusions: Magnetic resonance images and shape modeling provides a reliable method for characterizing vertebral shape in vivo. The method is able to identify differences between vertebral levels and between individuals. The use of these methods may be advantageous for performing repeated measurements in longitudinal studies., Level of Evidence: N/A., (Copyright © 2018 Scoliosis Research Society. Published by Elsevier Inc. All rights reserved.)

Purpose: Primarily to evaluate the radiation dose delivered to patients with obesity in projection radiography and its relationship to the patient's size. A secondary purpose is to estimate the subsequent projected radiation-related lifetime cancer risk to patients with obesity compared to normal-weight patients., Method and Material: Data from 1964 patients from a bariatric clinic in the UK were reviewed with the relevant permission. 630 patients were identified to have a projection radiography history and were included in the study. Patients' dose area product (DAP) data were collected for all projection radiography. Multiple exams in one day including a single DAP reading and exams with no records of DAP and exposure factors were excluded. Correlations were calculated and data analysed to yield the third quartile for each examination using STATA 14. Absorbed doses were generated from PCXMC simulation, utilising DAP data from this study and the UK national diagnostic reference level (NDRL), to calculate the effective risk for patients with obesity compared to patients with normal-weight., Results: Patients with obesity received higher DAPs for all examinations included in this study compared to NDRL. Abdominal and lumbar spine radiographs DAPs were the highest (17.6 and 30.31 Gy cm 2 ) compared to the NDRL (2.5 and 4 Gy cm 2 ). Only moderate to low correlations were found between patient's size and DAPs in the abdomen and chest radiographs. The projected radiation-related lifetime cancer risk for patients with obesity is up to 153% higher than for adult patients with normal weight., Conclusion: Patients with obesity receive higher DAPs than normal-weight adults which may be in excess of that expected due to their size. Therefore, radiation-related lifetime cancer risk is increased in patients with obesity as a result of medical radiation exposures. This indicates more dose optimisation research is needed in this group of patients to reduce dose rate and variation.

Objective: Lifting postures are frequently implicated in back pain. We previously related responses to a static load with intrinsic spine shape, and here we investigate the role of lumbar spine shape in lifting kinematics., Methods: Thirty healthy adults (18-65 years) performed freestyle , stoop and squat lifts with a weighted box (6-15 kg, self-selected) while being recorded by Vicon motion capture. Internal spine shape was characterised using statistical shape modelling (SSM) from standing mid-sagittal MRIs. Associations were investigated between spine shapes quantified by SSM and peak flexion angles., Results: Two SSM modes described variations in overall lumbar curvature (mode 1 (M1), 55% variance) and the evenness of curvature distribution (mode 2 (M2), 12% variance). M1 was associated with greater peak pelvis (r=0.38, p=0.04) and smaller knee flexion (r=-0.40, p=0.03) angles; individuals with greater curviness preferred to lift with a stooped lifting posture. This was confirmed by analysis of those individuals with very curvy or very straight spines (|M1|>1 SD). There were no associations between peak flexion angles and mode scores in stoop or squat trials (p>0.05). Peak flexion angles were positively correlated between freestyle and squat trials but not between freestyle and stoop or squat and stoop , indicating that individuals adjusted knee flexion while maintaining their preferred range of lumbar flexion and that 'squatters' adapted better to different techniques than 'stoopers'., Conclusion: Spinal curvature affects preferred lifting styles, and individuals with curvier spines adapt more easily to different lifting techniques. Lifting tasks may need to be tailored to an individual's lumbar spine shape., Competing Interests: Competing interests: None declared.

Objectives: To investigated the accuracy of computer-aided detection (CAD) software in musculoskeletal projection radiography via a systematic review., Key Findings: Following selection screening, eligible studies were assessed for bias, and had their study characteristics extracted resulting in 22 studies being included. Of these 22 three studies had tested their CAD software in a clinical setting; the first study investigated vertebral fractures, reporting a sensitivity score of 69.3% with CAD, compared to 59.8% sensitivity without CAD. The second study tested dental caries diagnosis producing a sensitivity score of 68.8% and specificity of 94.1% with CAD, compared to sensitivity of 39.3% and specificity of 96.7% without CAD. The third indicated osteoporotic cases based on CAD, resulting in 100% sensitivity and 81.3% specificity., Conclusion: The current evidence reported shows a lack of development into the clinical testing phase; however the research does show future promise in the variation of different CAD systems., (Copyright © 2017 The College of Radiographers. Published by Elsevier Ltd. All rights reserved.)

Finite element (FE) models driven by medical image data can be used to estimate subject-specific spinal biomechanics. This study aimed to combine magnetic resonance (MR) imaging and quantitative fluoroscopy (QF) in subject-specific FE models of upright standing, flexion and extension. Supine MR images of the lumbar spine were acquired from healthy participants using a 0.5 T MR scanner. Nine 3D quasi-static linear FE models of L3 to L5 were created with an elastic nucleus and orthotropic annulus. QF data was acquired from the same participants who performed trunk flexion to 60° and trunk extension to 20°. The displacements and rotations of the vertebrae were calculated and applied to the FE model. Stresses were averaged across the nucleus region and transformed to the disc co-ordinate system (S1 = mediolateral, S2 = anteroposterior, S3 = axial). In upright standing S3 was predicted to be -0.7 ± 0.6 MPa (L3L4) and -0.6 ± 0.5 MPa (L4L5). S3 increased to -2.0 ± 1.3 MPa (L3L4) and -1.2 ± 0.6 MPa (L4L5) in full flexion and to -1.1 ± 0.8 MPa (L3L4) and -0.7 ± 0.5 MPa (L4L5) in full extension. S1 and S2 followed similar patterns; shear was small apart from S23. Disc stresses correlated to disc orientation and wedging. The results demonstrate that MR and QF data can be combined in a participant-specific FE model to investigate spinal biomechanics in vivo and that predicted stresses are within ranges reported in the literature., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The kinematics information from imaging, if combined with optimization-based biomechanical models, may provide a unique platform for personalized assessment of trunk muscle forces (TMFs). Such a method, however, is feasible only if differences in lumbar spine kinematics due to differences in TMFs can be captured by the current imaging techniques. A finite element model of the spine within an optimization procedure was used to estimate segmental kinematics of lumbar spine associated with five different sets of TMFs. Each set of TMFs was associated with a hypothetical trunk neuromuscular strategy that optimized one aspect of lower back biomechanics. For each set of TMFs, the segmental kinematics of lumbar spine was estimated for a single static trunk flexed posture involving, respectively, 40° and 10° of thoracic and pelvic rotations. Minimum changes in the angular and translational deformations of a motion segment with alterations in TMFs ranged from 0° to 0.7° and 0 mm to 0.04 mm, respectively. Maximum changes in the angular and translational deformations of a motion segment with alterations in TMFs ranged from 2.4° to 7.6° and 0.11 mm to 0.39 mm, respectively. The differences in kinematics of lumbar segments between each combination of two sets of TMFs in 97% of cases for angular deformation and 55% of cases for translational deformation were within the reported accuracy of current imaging techniques. Therefore, it might be possible to use image-based kinematics of lumbar segments along with computational modeling for personalized assessment of TMFs., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: Oxidative stress (OS) negatively affects skeletal muscle homeostasis in experimental models of ageing. However, little is known about the associations between circulating OS markers and parameters of muscle mass and function, and their responses to exercise training, in humans., Methods: Maximal voluntary contraction (MVC, primary outcome) and isokinetic torque of the knee extensors at 30° s -1 (MIT), muscle cross-sectional area (MCSA) and quality (MQ, secondary outcomes), and plasma concentrations of malondialdehyde (MDA, pro-OS), homocysteine (HCY, pro-OS), taurine (TAU, anti-OS), and protein sulphydryl groups (PSH, anti-OS) were measured in 27 healthy older males and 23 females at baseline and after an 18-week resistance exercise program, with or without a nutritional intervention (fish oil vs. placebo)., Results: After adjusting for age, glomerular filtration rate, and nutritional intervention, there were no significant correlations between baseline OS markers and muscle parameters, barring a positive association between TAU and MIT in females (r = 0.53, P = .035) and between MDA and MCSA in males (r = 0.69, P = .001). Training did not significantly change OS markers, except for a reduction in MDA in females (-0.27 μmol/L, 95% CI -0.51 to -0.02, P = .034). In females, there were significant correlations between baseline MDA and exercise-induced changes in MVC (P = .018), baseline TAU and changes in MCSA (P = .026), and baseline HCY and changes in MCSA (P = .046) and MQ (P = .022). In males, baseline MDA was significantly associated with exercise-induced changes in MVC (P = .040)., Conclusions: Plasma MDA, HCY, and TAU were significantly associated with baseline and/or exercise-induced changes in muscle mass and function in healthy older adults, primarily in females. Pending further confirmation in other populations, specific OS markers, particularly MDA, might predict muscle responses to resistance exercise programs in old age., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Objectives: The current study was designed to explore the associations between L-arginine metabolites and muscle mass and function in old age, which are largely unknown., Design: The study used a randomised, double-blind, placebo-controlled design., Setting: The study was carried out in a laboratory setting., Participants: 50 healthy older adults [median age 70 years (IQR 67-73); 27 males]., Intervention: Participants undertook an 18-week resistance exercise program, and a nutritional intervention (fish oil vs. placebo)., Measurements: Serum homoarginine, ornithine, citrulline, asymmetric dimethylarginine (ADMA), NG-monomethyl-L-arginine (L-NMMA), and symmetric dimethylarginine (SDMA), maximal voluntary contraction (MVC) and isokinetic torque of the knee extensors at 30° s-1 (MIT), muscle cross sectional area (MCSA) and quality (MQ) were measured at baseline and after the intervention., Results: No significant exercise-induced changes were observed in metabolite concentrations. There were significant sex differences in the associations between metabolites and muscle parameters. After adjusting for age, glomerular filtration rate and fish oil intervention, citrulline (P=0.002) and ornithine (P=0.022) were negatively associated with MCSA at baseline in males but not females. However, baseline citrulline was negatively correlated with exercise-induced changes in MVC (P=0.043) and MQ (P=0.026) amongst females. Furthermore, amongst males, baseline homoarginine was positively associated with exercise-induced changes in MVC (P=0.026), ADMA was negatively associated with changes in MIT (P=0.026), L-NMMA (p=0.048) and ornithine (P<0.001) were both positively associated with changes in MCSA, and ornithine was negatively associated with changes in MQ (P=0.039)., Conclusion: Therefore, barring citrulline, there are significant sex differences in the associations between L-arginine metabolites and muscle mass and function in healthy older adults. These metabolites might enhance sarcopenia risk stratification, and the success of exercise programs, in old age., Competing Interests: The authors do not have any conflicts of interest to declare.

Needle puncture of the intervertebral disc can initiate a mechanical and biochemical cascade leading to disc degeneration. Puncture's mechanical effects have been shown near the puncture site, mechanical effects should be observed far, relative to needle size, from the puncture site, given the disc-wide damage induced by the stab. The aim of this work was to quantify these far-field effects, and to observe the local structural damage provoked by the needle. Strips of cow tail annulus fibrosus underwent two consecutive mechanical loadings to 5% tensile strain; fifteen samples were punctured in a radial direction with a randomly assigned needle between the two loadings (needle gauges between 19 and 23). Ten samples (control group) were not punctured. During loading, the tissue strains were imaged using second harmonic generation microscopy in a <600×800µm region about 4.4mm from the puncture site. After mechanical testing, the puncture site was imaged in 3D. Puncture had no significant effect on annulus elastic modulus. Imaging showed a modest change in the shearing between fibre bundles however, the linear strain between bundles, intra-bundle shear and linear strain were not significantly affected. At the puncture site, detached lumps of tissue were present. These results suggest that the mechanical effects observed in intact discs are due to the depressurization of the disc, rather than the local damage to the annulus. Needle profiles could be designed, aiming at separating fibre bundles rather than cutting through them, to avoid leaving dying tissue behind., Statement of Significance: Needle puncture of the intervertebral disc can initiate a mechanical and biochemical cascade leading to disc degeneration, but the link between the local damage of the puncture and the disc-wide effects is not well understood. This work aimed at determining the micro-mechanical effects of the puncture far from its site, and to observe the damage induced by the puncture with high resolution imaging. Results show that the puncture had modest effect far from the puncture, but lumps of tissue were left by the needle, detached from the disc; these could cause further damage through friction and inflammation of the surrounding tissues. This suggests that the cascade leading to degeneration is probably driven by a biochemical response rather than disc-wide mechanical effects., (Copyright © 2017 Acta Materialia Inc. All rights reserved.)

Background: Exercise of the spinal muscles is recommended for a variety of rehabilitative reasons but it is not always clear whether interventions are effective in improving the performance of the muscles or whether their benefit is elicited via other mechanisms., Objective: To explore the effects of an exercise intervention on the size and exercise performance of the lumbar spine extensor muscles., Methods: Eleven healthy participants undertook a four week programme of exercise. Magnetic resonance imaging and phosphorus spectroscopy were performed before and after the intervention to determine the time to fatigue and phosphocreatine (PCr) depletion during a muscle endurance test (modified Biering-Sørensen) together with muscle cross-sectional area (CSA)., Results: The post intervention measures were significantly different to the pre-intervention results for the time to fatigue (post-pre: 20.5 ± 22.7 s (P= 0.014)) and PCr depletion both at the point of fatigue (post-pre: 9.5 ± 11.9% (P= 0.024)) and at a matched time-point (post-pre: 12.2 ± 11.9% (P= 0.007)). CSA was not significantly different in any muscle., Conclusions: Exercise improved the performance of the trunk muscles despite no impact on CSA. This demonstrated the importance of obtaining a wide range of measures when assessing the effectiveness of exercise intervention programmes.

The complex structure of the annulus fibrosus is strongly related to its mechanical properties. Recent work showed that it is possible to observe the relative movement of fibre bundles in loaded cow tail annulus; the aim of this work was to describe and quantify annulus fibrosus micromechanics in degenerated human disc, and compare it with cow tail annulus, an animal model often used in the literature. Second harmonic generation was used to image the collagen matrix in twenty strips of annulus fibrosus harvested from intervertebral disc of seven patients undergoing surgery. Samples were loaded to 6% tensile strain in 1% steps. Elastic modulus was calculated from loading curves, and micromechanical strains were calculated from the images using custom software. The same protocol was applied to twenty strips of annulus harvested from cow tail discs. Significant morphological differences were found between human and cow tail samples, the most striking being the lack of collagen fibre crimp in the former. Fibres were also observed bending and running from one lamella to the other, forming a strong flexible interface. Interdigitation of fibre bundles was also present at this interface. Quantitative results show complex patterns of inter-bundle and inter-lamellar behaviour, with inter-bundle sliding being the main strain mechanism. Elastic modulus was similar between species, and it was not affected by the degree of degeneration. This work gives an insight into the complex structure and mechanical function of the annulus fibrosus, which should be accounted for in disc numerical modelling.

Background: We previously measured the rate of regaining muscle strength during rehabilitation of lower leg muscles in patients following lower leg casting. Our primary aim in this study was to measure the rate of gain of strength in healthy individuals undergoing a similar training regime. Our secondary aim was to test the ability of MRI to provide a biomarker for muscle function., Methods: Men and women were recruited in three age groups: 20-30, 50-65 and over 70 years. Their response to resistance training of the right lower leg twice a week for 8 weeks was monitored using a dynamometer and MRI of tibialis anterior, soleus and gastrocnemius muscles at 2 weekly intervals to measure muscle size (anatomical cross-sectional area ( ACSA )) and quality ( T 2 relaxation). Forty-four volunteers completed the study., Results: Baseline strength declined with age. Training had no effect in middle-aged females or in elderly men in dorsiflexion. Other groups significantly increased both plantarflexion and dorsiflexion strength at rates up to 5.5 N m week -1 in young females in plantarflexion and 1.25 N m week -1 in young males in dorsiflexion. No changes were observed in ACSA or T 2 in any age group in any muscle., Conclusion: Exercise training improves muscle strength in males at all ages except the elderly in dorsiflexion. Responses in females were less clear with variation across age and muscle groups. These results were not reflected in simple MRI measures that do not, therefore, provide a good biomarker for muscle atrophy or the efficacy of rehabilitation., Competing Interests: Competing interests: None declared.

Background: Resistance exercise increases muscle mass and function in older adults, but responses are attenuated compared with younger people. Data suggest that long-chain n-3 polyunsaturated fatty acids (PUFAs) may enhance adaptations to resistance exercise in older women. To our knowledge, this possibility has not been investigated in men., Objective: We sought to determine the effects of long-chain n-3 PUFA supplementation on resistance exercise training-induced increases in muscle mass and function and whether these effects differ between older men and women., Design: Fifty men and women [men: n = 27, mean ± SD age: 70.6 ± 4.5 y, mean ± SD body mass index (BMI; in kg/m 2 ): 25.6 ± 4.2; women: n = 23, mean ± SD age: 70.7 ± 3.3 y, mean ± SD BMI: 25.3 ± 4.7] were randomly assigned to either long-chain n-3 PUFA (n = 23; 3 g fish oil/d) or placebo (n = 27; 3 g safflower oil/d) and participated in lower-limb resistance exercise training twice weekly for 18 wk. Muscle size, strength, and quality (strength per unit muscle area), functional abilities, and circulating metabolic and inflammatory markers were measured before and after the intervention., Results: Maximal isometric torque increased after exercise training to a greater (P < 0.05) extent in the long-chain n-3 PUFA group than in the placebo group in women, with no differences (P > 0.05) between groups in men. In both sexes, the effect of exercise training on maximal isokinetic torque at 30, 90, and 240° s -1 , 4-m walk time, chair-rise time, muscle anatomic cross-sectional area, and muscle fat did not differ (P > 0.05) between groups. There was a greater (P < 0.05) increase in muscle quality in women after exercise training in the long-chain n-3 PUFA group than in the placebo group, with no such differences in men (P > 0.05). Long-chain n-3 PUFAs resulted in a greater decrease (P < 0.05) than the placebo in plasma triglyceride concentrations in both sexes, with no differences (P > 0.05) in glucose, insulin, or inflammatory markers., Conclusion: Long-chain n-3 PUFA supplementation augments increases in muscle function and quality in older women but not in older men after resistance exercise training. This trial was registered at clinicaltrials.gov as NCT02843009.

Subject-specific parameters influence spinal loads and the risk of back disorders but their relative effects are not well understood. The objective of this study is to investigate the effects of changes in age (35-60 years), sex (male, female), body height (BH: 150-190cm) and body weight (BW: 50-120kg) on spinal loads in a full-factorial simulation using a personalized (spine kinematics, geometry, musculature and passive properties) kinematics driven musculoskeletal trunk finite element model. Segmental weight distribution (magnitude and location along the trunk) was estimated by a novel technique to accurately represent obesity. Five symmetric sagittal loading conditions were considered, and main effect plots and analyses of variance were employed to identify influential parameters. In all 5 tasks simulated, BW (98.9% in compression and 96.1% in shear) had the greatest effect on spinal loads at the L4-L5 and L5-S1 levels followed by sex (0.7% in compression and 2.1% in shear), BH (0.4% in compression and 1.5% in shear) and finally age (<5.4%). At identical BH and BW, spinal loads in females were slightly greater than those in males by ~4.7% in compression and ~8.7% in shear. In tasks with no loads in hands, BW-normalized spinal loads further increased with BW highlighting the exponential increase in spinal loads with BW that indicates the greater risk of back disorders especially in obese individuals. Uneven distribution of weight in obese subjects, with more BW placed at the lower trunk, further (though slightly <7.5%) increased spinal loads., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Resistance exercise training is known to be effective in increasing muscle mass in older people. Acute measurement of protein metabolism data has indicated that the magnitude of response may differ between sexes. We compared adaptive responses in muscle mass and function to 18 weeks resistance exercise training in a cohort of older (>65 years) men and women. Resistance exercise training improved knee extensor maximal torque, 4 m walk time, time to complete five chair rises, muscle anatomical cross-sectional area (ACSA) and muscle quality with no effect on muscle fat/water ratio or plasma glucose, insulin, triacylglycerol, IL-6, and TNF-α Differences between sexes were observed for knee extensor maximal torque and muscle quality with greater increases observed in men versus women (P < 0.05). Maximal torque increased by 15.8 ± 10.6% in women and 41.7 ± 25.5% in men, whereas muscle quality increased by 8.8 ± 17.5% in women and by 33.7 ± 25.6% in men. In conclusion, this study has demonstrated a difference in the magnitude of adaptation, of some of the outcome measures employed, in response to 18 weeks of resistance exercise training between men and women. The mechanisms underlying this observation remain to be established., (© 2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.)

Unlabelled: The intervertebral disc is a multicomposite structure, with an outer fibrous ring, the annulus fibrosus, retaining a gel-like core, the nucleus pulposus. The disc presents complex mechanical behaviour, and it is of high importance for spine biomechanics. Advances in multiscale modelling and disc repair raised a need for new quantitative data on the finest details of annulus fibrosus mechanics. In this work we explored inter-lamella and inter-bundle behaviour of the outer annulus using micromechanical testing and second harmonic generation microscopy. Twenty-one intervertebral discs were dissected from cow tails; the nucleus and inner annulus were excised to leave a ring of outer annulus, which was tested in circumferential loading while imaging the tissue's collagen fibres network with sub-micron resolution. Custom software was developed to determine local tissue strains through image analysis. Inter-bundle linear and shear strains were 5.5 and 2.8 times higher than intra-bundle strains. Bundles tended to remain parallel while rotating under loading, with large slipping between them. Inter-lamella linear strain was almost 3 times the intra-lamella one, but no slipping was observed at the junction between lamellae. This study confirms that outer annulus straining is mainly due to bundles slipping and rotating. Further development of disc multiscale modelling and repair techniques should take into account this modular behaviour of the lamella, rather than considering it as a homogeneous fibre-reinforced matrix., Statement of Significance: The intervertebral disc is an organ tucked between each couple of vertebrae in the spine. It is composed by an outer fibrous layer retaining a gel-like core. This organ undergoes severe and repeated loading during everyday life activities, since it is the compliant component that gives the spine its flexibility. Its properties are affected by pathologies such as disc degeneration, a major cause of back pain. In this article we explored the micromechanical behaviour of the disc's outer layer using second harmonic generation, a technique which allowed us to visualize, with unprecedented detail, how bundles of collagen fibres slide relative to each other when loaded. Our results will help further the development of new multiscale numerical models and repairing techniques., (Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Finite element (FE) modelling is an established technique for investigating spinal biomechanics. Using image data to produce FE models with subject-specific geometry and displacement boundary conditions may help extend their use to the assessment spinal loading in individuals. Lumbar spine magnetic resonance images from nine participants in the supine, standing and sitting postures were obtained and 2D poroelastic FE models of the lumbar spine were created from the supine data. The rigid body translation and rotation of the vertebral bodies as the participant moved to standing or sitting were applied to the model. The resulting pore pressure in the centre of the L4/L5 disc was determined and the sensitivity to the material properties and vertebral body displacements was assessed. Although the limitations of using a 2D model mean the predicted pore pressures are unlikely to be accurate, the results showed that subject-specific variation in geometry and motion during postural change leads to variation in pore pressure. The model was sensitive to the Young׳s modulus of the annulus matrix, the permeability of the nucleus, and the vertical translation of the vertebrae. This study demonstrates the feasibility of using image data to drive subject-specific lumbar spine FE models and indicates where further development is required to provide a method for assessing spinal biomechanics in a wide range of individuals., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Purpose: We have previously shown that the lumbar spine has an intrinsic shape specific to the individual and characteristic of sitting, standing and supine postures. The purpose of this study was to test the hypothesis that this intrinsic shape is detectable throughout a range of postures from extension to full flexion in healthy adults., Methods: Sagittal images of the lumbar spine were taken using a positional MRI with participants (n = 30) adopting six postures: seated extension, neutral standing, standing with 30, 45 and 60° and full flexion. Active shape modelling (ASM) was used to identify and quantify 'modes' of variation in the shape of the lumbar spine., Results: ASM showed that 89.5% of the variation in the shape of the spine could be explained by the first two modes; describing the overall curvature and the distribution of curvature of the spine. Mode scores were significantly correlated between all six postures (modes 1-9, r = 0.4-0.97, P < 0.05), showing that an element of intrinsic shape was maintained when changing postures. The spine was most even in seated extension (P < 0.001) and most uneven between 35 and 45° flexion (P < 0.05)., Conclusions: This study shows that an individual's intrinsic lumbar spine shape is quantifiable and detectable throughout lumbar flexion and extension. These findings will enable the role of lumbar curvature in injury and low back pain to be assessed in the clinic and in the working and recreational environments.

A previous modelling study predicted that the forces applied by the extensor muscles to stabilise the lumbar spine would be greater in spines that have a larger sagittal curvature (lordosis). Because the force-generating capacity of a muscle is related to its size, it was hypothesised that the size of the extensor muscles in a subject would be related to the size of their lumbar lordosis. Magnetic resonance imaging (MRI) data were obtained, together with age, height, body mass and back pain status, from 42 female subjects. The volume of the extensor muscles (multifidus and erector spinae) caudal to the mid-lumbar level was estimated from cross-sectional area measurements in axial T1-weighted MRIs spanning the lumbar spine. Lower lumbar curvature was determined from sagittal T1-weighted images. A stepwise linear regression model was used to determine the best predictors of muscle volume. The mean lower lumbar extensor muscle volume was 281 cm(3) (SD = 49 cm(3)). The mean lower lumbar curvature was 30 ° (SD = 7 °). Five subjects reported current back pain and were excluded from the regression analysis. Nearly half the variation in muscle volume was accounted for by the variables age (standardised coefficient, B = -3.2, P = 0.03) and lower lumbar curvature (B = 0.47, P = 0.002). The results support the hypothesis that extensor muscle volume in the lower lumbar spine is related to the magnitude of the sagittal curvature; this has implications for assessing muscle size as an indicator of muscle strength., (© 2013 Anatomical Society.)

Purpose: To investigate MRI biomarkers of muscle atrophy during cast immobilization of the lower leg., Materials and Methods: Eighteen patients (8 male, 10 female), who had one lower leg immobilized in a cast, underwent 3.0 Tesla (T) MR imaging 5, 8, 15, 29, and 43 days after casting. Measurements were made on both lower legs of total muscle volume. Cross-sectional area (CSA), fractional water content, and T(2) were measured in tibialis anterior (TA), gastrocnemius medialis (GM) and lateralis (GL) and soleus (SOL). Fiber pennation angle was measured in GM., Results: Total muscle volume decreased by 17% (P < 0.001) over the 6 weeks of immobilization. The greatest loss in CSA (mean[SD]) was seen in GM (-23.3(8.7)%), followed by SOL (-19.0(9.8)%), GL (-17.1(6.5)%), and TA (-10.7(5.9)%). Significant reductions of CSA were also detectable in the contra-lateral leg. T(2) increased in all muscles: TA 27.0(2.5) ms to 29.6(2.8) ms (P < 0.001), GM 34.6(2.9) ms to 39.8(5.4) ms (P < 0.001) and SOL 34.4 (2.9) ms to 44.9(5.9) ms (P < 0.001). Small reductions were found in fractional water content. Pennation angle decreased in the cast leg (P < 0.001)., Conclusion: Quantitative MR imaging can detect and monitor progressive biochemical and biophysical changes in muscle during immobilization., (Copyright © 2011 Wiley-Liss, Inc.)

The 2D shape of the lumbar spine in the sagittal plane can be determined from lordosis angles measured between the corresponding end-plates of the vertebral bodies or by using an active shape model (ASM) of the vertebral body outline. The ASM was previously shown to be a more efficient and reliable method, but its accuracy has not been assessed. The aim of this study was to determine the accuracy of an ASM for characterising lumbar spine shape and compare this to conventional measurements. Images of 25 different lumbar spine shapes were generated and measured, using both methods, by three independent observers. The accuracy of the ASM, determined from lordosis angles predicted by the model, was found to be better than conventional measurements.

The shape of the lumbar spine in the sagittal plane varies between individuals and as a result of postural changes but it is not known how the shape in different postures is related. Sagittal images of the lumbar spines of 24 male volunteers were acquired using a positional magnetic resonance scanner. The subjects were imaged lying supine, standing and sitting. An active shape model was used to characterize shape in terms of independent modes of variation. Two modes were identified that described the total (mode 1) and distribution (mode 2) of the curvature. The spinal shape was found to be intercorrelated between the three postures for both modes, suggesting that the lumbar spine has an element of shape that is partially maintained despite postural alterations. Mode 1 values indicated that the spine was straightest when standing and curviest when sitting. Mode 2 values indicated that the distribution in the curvature was most even when sitting and least even when lying supine. Systematic differences in the behaviour of the spine, when changing posture, were found that suggest that the shape of the spine may affect its biomechanics.

Determining the effect of load carriage on the human spine in vivo is important for determining spinal forces and establishing potential mechanisms of back injury. Previous studies have suggested that the natural curvature of the spine straightens under load, but are based on modelling and external measurements from the surface of the back. In the current study, an upright positional MRI scanner was used to acquire sagittal images of the lumbar and lower thoracic spine of 24 subjects. The subjects were imaged in standing whilst supporting 0, 8 and 16 kg of load which was applied axially across the shoulders using an apron. An active shape model of the vertebral bodies from T10 to S1 was created and used to characterise the effect of load. The results from the shape model showed that the behaviour of the average-shaped spine was to straighten slightly. However, the shape model also showed that the effect of load exhibited systematic variation between individuals. Those who had a smaller than average curvature before loading straightened under load, whereas those who had a greater than average curvature before loading showed an increase in curvature under load. The variation in behaviour of differently shaped spines may have further implications for the effects of load in lifting manoeuvres and in understanding the aetiology of back pain.

Unlike engineering fibre composite materials which comprise of fibres that are uniform cylindrical in shape, collagen fibrils reinforcing the proteoglycan-rich (PG) gel in the extra-cellular matrices (ECMs) of connective tissues are taper-ended (paraboloidal in shape). In an earlier paper we have discussed how taper of a fibril leads to an axial stress up-take which differs from that of a uniform cylindrical fibre and implications for fibril fracture. The present paper focuses on the influence of fibre aspect ratio, q (slenderness), and Young's modulus (stiffness), relative to that of the gel phase, E(R), on the magnitude of the axial tensile stresses generated within a fibril and wider implications on failure at tissue level. Fibre composite models were evaluated using finite element (FE) and mathematical analyses. When the applied force is low, there is elastic stress transfer between the PG gel and a fibril. FE modelling shows that the stress in a fibril increases with E(R) and q. At higher applied forces, there is plastic stress transfer. Mathematical modelling predicts that the stress in a fibril increases linearly with q. For small q values, fibrils may be regarded as fillers with little ability to provide tensile reinforcement. Large q values lead to high stress in a fibril. Such high stresses are beneficial provided they do not exceed the fracture stress of collagen. Modulus difference regulates the strain energy release density, u, for interfacial rupture; large E(R) not only leads to high stress in a fibril but also insures against interfacial rupture by raising the value of u.

Synthetic bone graft substitutes have been developed for impaction grafting revision hip surgery in response to concerns about the availability and potential infection risk of allograft. We performed an in vitro experiment to determine whether a synthetic porous hydroxyapatite material might improve resistance to cumulative subsidence and cyclic (elastic) movement on loading. We impacted different ratios of hydroxyapatite and allograft (0%, 50%, 70%, and 90% hydroxyapatite) into composite femoral models (eight per group) and implanted tapered, polished stems with cement. Models were loaded for 18,000 cycles on a servohydraulic materials testing machine. Migration of the femoral prostheses and the distal cement was determined using radiostereometric analysis, and cyclic movement was measured mechanically by the testing machine. Hydroxyapatite decreased overall subsidence and subsidence at the prosthesis-cement interface, but there was no difference at the cement-femur interface. This decrease may have occurred because the hydroxyapatite-containing graft was more rigid, or because it resulted in a thicker cement mantle. Cyclic prosthesis movement also was lower with hydroxyapatite. While the biologic response to porous hydroxyapatite remains to be determined, its mechanical properties appear promising.

A mechanism for the postural balance of the human torso over the hip joints is reported that does not appear to have been fully recognised. The centre of gravity of the torso is usually considered poised above the hips. This is in a state of unstable equilibrium. Here, we propose that body weight acting through the sacrum is counter-balanced by tension in the ilio-femoral ligament; the hips acting as the fulcrum. This places the torso in stable equilibrium and means that balance may be maintained with minimal muscular forces. The joint reaction force due to this mechanism in a two-legged stance is then of the order of the body-weight on each hip. An implication is that capsular ligaments are important and consideration should be given to retaining or restoring them as much as possible in hip arthroplasty.

Collagen fibrils provide tensile reinforcement for extracellular matrix. In at least some tissues, the fibrils have a paraboloidal taper at their ends. The purpose of this paper is to determine the implications of this taper for the function of collagen fibrils. When a tissue is subjected to low mechanical forces, stress will be transferred to the fibrils elastically. This process was modelled using finite element analysis because there is no analytical theory for elastic stress transfer to a non-cylindrical fibril. When the tissue is subjected to higher mechanical forces, stress will be transferred plastically. This process was modelled analytically. For both elastic and plastic stress transfer, a paraboloidal taper leads to a more uniform distribution of axial tensile stress along the fibril than would be generated if it were cylindrical. The tapered fibril requires half the volume of collagen than a cylindrical fibril of the same length and the stress is shared more evenly along its length. It is also less likely to fracture than a cylindrical fibril of the same length in a tissue subjected to the same mechanical force.

Analysis of the diameters of collagen fibrils provides insight into the structure and physical processes occurring in the tissue. This paper describes a method for analyzing the frequency distribution of the diameters of collagen fibrils from small-angle X-ray scattering (SAXS) patterns. Frequency values of fibril diameters were input into a mathematical model of the form factor to calculate the equatorial intensity which best fits the experimentally derived data from SAXS patterns. A minimization algorithm utilizing simulated annealing (SA) was used in the fitting procedure. The SA algorithm allowed for random sampling of the frequency values, and was run iteratively to build up an optimized frequency distribution of fibril diameters. Results were obtained for collagen samples from sheep spine ligaments. The mean fibril diameter value obtained from this data-fitting method was 73 nm+/-20 nm (S.D.). From scanning transmission electron microscopy, the mean diameter was found to be 69 nm+/-14 nm (S.D.). The good agreement between the two methods demonstrates the reliability of the SAXS method for the tissue examined. The non-destructive nature of this technique, as well as its statistical robusticity and capacity for large sampling, means that this method is both quick and effective.

Fused deposition modelling (FDM) is a new method for rapid prototyping, a technique that produces models of objects from computer files. The most commonly used rapid prototyping technique for medical applications is stereolithography, but FDM has several potential advantages. This paper is concerned with the accuracy of an FDM model of a sheep lumbar vertebra using data from a CT scan. The model and the original vertebra were compared by making measurements with vernier callipers and by laser scanning. Visually, the model reproduced the features of the original object; this conclusion was supported by a comparison of the laser scans. Discrepancies in measurements were comparable with those of models produced using other rapid prototyping techniques, demonstrating that FDM is a viable method for making models for clinical use.

Poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels have been used, or suggested for use, in a wide range of biomedical applications. In many of these applications, the mechanical properties of the gel are important for its proper functioning. These properties are influenced by a number of factors, including water content. In this study the storage and loss shear moduli were measured as a function of frequency for gels with water contents ranging from 22% to 48% at a temperature of 37 degrees C. At low frequencies and high water contents, deformation frequency had little effect. However, at higher frequencies and lower water contents, both moduli increased markedly with increasing frequency. This can be explained by the gels approaching a glass transition. The curves describing the behavior of each gel were combined to form a master curve, using a method analogous to the time-temperature superposition principle. This master curve can be used to predict the shear moduli for gels with a wide range of water contents and loading frequencies. For example, for a gel with a water content of 47.8% (as a percentage of the mass of gel), the curve provides shear moduli values over a frequency range of 10(-2)-10(4) Hz.

Statistical methods allow the effects of uncertainty to be incorporated into finite element models. This has potential benefits for the analysis of biological systems where natural variability can give rise to substantial uncertainty in both material and geometrical properties. In this study, a simple model of the intervertebral disc under compression was created and analysed as both a deterministic and a stochastic system. Factorial analysis was used to determine the important parameters to be included in the stochastic analysis. The predictions from the model were compared to experimental results from 21 sheep discs. The size and shape of the distribution of the axial deformations predicted by the model was consistent with the experimental results given that the number of model solutions far exceeded the number of experimental results. Stochastic models could be valuable in determining the range and most likely value of stress in a tissue or implant.

A finite element model of the knee meniscus was developed to investigate the effects of various geometrical and material properties on the behaviour of the meniscus under compressive load. Factorial methods were used to determine the relative effect of varying the properties by +/-10% of their initial value. It was found that the stresses in the meniscus were more sensitive to geometry (meniscus width and radius of curvature of the femoral surface of the meniscus) than material properties. The model was also used to investigate the effect of incongruency between the radius of curvature of the femur and the femoral surface of the meniscus. It was shown that mismatch between the curvatures of the femur and meniscus has a large effect on the stresses both in the meniscus and in the underlying cartilage. The results from the study have implications for the design and development of meniscal repair devices and replacements.

The influence of water on the physical properties of a hydrogel is important for understanding natural tissues and in designing synthetic materials to replace them. In this study, poly (2-hydroxyethyl methacrylate) (pHEMA) was used as a model system to understand how water interacts with the polymer of a hydrogel. Thermal analysis methods (thermogravimetric analysis coupled to mass spectrometry and differential scanning calorimetry) were used to determine: (i) the total water content of pHEMA gels; (ii) how this water was lost during heating; (iii) the relationship between water content of the gel and its glass transition temperature; and (iv) the behavior of the water in the gel on cooling. Previous researchers have invoked various models to describe the organization of water in a hydrogel. In this study, the simplest model which could explain all of the results from the different thermal analysis techniques was one which consisted of three classes of water: (i) hydration water in close proximity to the polymer; (ii) interstitial water in regions or cavities surrounded by polymer chains; and (iii) bulk water.

Finite element analysis (FEA) is a commonly used tool within many areas of engineering and can provide useful information in structural analysis of mechanical systems. However, most analyses within the field of biomechanics usually take no account either of the wide variation in material properties and geometry that may occur in natural tissues or manufacturing imperfections in synthetic materials. This paper discusses two different methods of incorporating uncertainty in FE models. The first, Taguchi's robust parameter design, uses orthogonal matrices to determine how to vary the parameters in a series of FE models, and provides information on the sensitivity of a model to input parameters. The second, probabilistic analysis, enables the distribution of a response variable to be determined from the distributions of the input variables. The methods are demonstrated using a simple example of an FE model of a beam that is assigned material properties and geometry over a range similar to an orthopaedic fixation plate. In addition to showing how each method may be used on its own, we also show how computational effort may be minimised by first identifying the most important input variables before determining the effects of imprecision.

Objective: To determine the water content, collagen content and collagen orientation angle in different regions of sheep lumbar discs., Design: A laboratory study of sheep discs obtained from an abattoir., Methods: A total of 21 sheep lumbar discs were obtained from three lumbar spines. Water content was determined by oven drying (60 degrees C) to constant mass. Collagen content was determined by hydroxyproline analysis. Fibre orientation angles were determined by X-ray diffraction., Results: Water content increased from 74% of total tissue mass in the outer annulus, to 82% in the inner annulus, to 86% in the nucleus. Collagen content decreased from 30% of total tissue mass in the outer region to 20% in the inner region of the anterior and lateral annulus; it was 16% in the posterior annulus. The orientation angle of the collagen fibres decreased from 59 degrees in the outer region to 56 degrees in the inner region of the anterior and lateral annulus; it was 51 degrees in the posterior annulus., Conclusions: Sheep lumbar intervertebral discs provide a reasonable model for human lumbar intervertebral discs., Relevance: Sheep lumbar discs have been used to investigate the effects of removing and replacing the nucleus. These studies indicate that removal of nucleus may lead to further disc degeneration and indicate the material properties required for an implant material. The relevance of these previous studies is increased if human and sheep lumbar discs have a similar composition and structure.

Objective: To determine whether replacement of the nucleus with a synthetic material would prevent the effects of nucleus removal., Design: Laboratory experiments on excised tissues and a finite element model., Background: Removal of the nucleus from the intervertebral disc causes the inner margins of the annulus to bulge inwards, instead of outwards, during compression. This may cause the annulus to degenerate further., Methods: Video recordings of sheep discs, sectioned in the sagittal plane, were obtained during compression in a materials testing machine; the cut face of the disc was sealed with a Perspex window. Experiments were repeated with the nucleus removed and then replaced by a synthetic implant. A finite element model of an intact disc was also used to investigate the effect of nucleus replacement., Results: When the nucleus of sectioned discs was replaced with the polymer materials, the inward bulging of the annulus was not observed. The predictions from the finite element model of the intact disc were consistent with this result., Conclusions: Replacement of the nucleus with a synthetic material can prevent the changes in annulus behaviour that result from removal of the nucleus., Relevance: A suitable implant to replace the nucleus after surgical removal may help prevent inward bulging of the inner layers of the annulus.