Biomechanical evaluation of Back injuries during typical snowboarding backward falls.

To prevent spinal and back injuries in snowboarding, back protector devices (BPDs) have been increasingly used. The biomechanical knowledge for the BPD design and evaluation remains to be explored in snowboarding accident conditions. This study aims to evaluate back-to-snow impact conditions and the associated back injury mechanisms in typical snowboarding backward falls. A previously validated snowboarder multi-body model was first used to evaluate the impact zones on the back and the corresponding impact velocities in a total of 324 snowboarding backward falls. The biomechanical responses during back-to-snow impacts were then evaluated by applying the back-to-snow impact velocity to a full human body finite element model to fall on the snow ground of three levels of stiffness (soft, hard, and icy snow). The mean values of back-to-snow normal and tangential impact velocities were 2.4 m/s and 7.3 m/s with maximum values up to 4.8 m/s and 18.5 m/s. The lower spine had the highest normal impact velocity during snowboarding backward falls. The thoracic spine was found more likely to exceed the limits of flexion-extension range of motions than the lumbar spine during back-to-snow impacts, indicating a higher injury risk. On the hard and icy snow, rib cage and vertebral fractures were predicted at the costal cartilage and the posterior elements of the vertebrae. Despite the possible back injuries, the back-to-snow impact force was always lower than the force thresholds of the current BPD testing standard. The current work provides additional biomechanical knowledge for the future design of back protections for snowboarders.

Investigating heartbeat-related in-plane motion and stress levels induced at the aortic root.

BACKGROUND: The axial motion of aortic root (AR) due to ventricular traction was previously suggested to contribute to ascending aorta (AA) dissection by increasing its longitudinal stress, but AR in-plane motion effects on stresses have never been studied. The objective is to investigate the contribution of AR in-plane motion to AA stress levels. METHODS: The AR in-plane motion was assessed on magnetic resonance imagining data from 25 healthy volunteers as the movement of the AA section centroid. The measured movement was prescribed to the proximal AA end of an aortic finite element model to investigate its influences on aortic stresses. The finite element model was developed from a patient-specific geometry using LS-DYNA solver and validated against the aortic distensibility. Fluid-structure interaction (FSI) approach was also used to simulate blood hydrodynamic effects on aortic dilation and stresses. RESULTS: The AR in-plane motion was 5.5 ± 1.7 mm with the components of 3.1 ± 1.5 mm along the direction of proximal descending aorta (PDA) to AA centroid and 3.0 ± 1.3 mm perpendicularly under the PDA reference system. The AR axial motion elevated the longitudinal stress of proximal AA by 40% while the corresponding increase due to in-plane motion was always below 5%. The stresses at proximal AA resulted approximately 7% less in FSI simulation with blood flow. CONCLUSIONS: The AR in-plane motion was comparable with the magnitude of axial motion. Neither axial nor in-plane motion could directly lead to AA dissection. It is necessary to consider the heterogeneous pressures related to blood hydrodynamics when studying aortic wall stress levels.

Spinal injury analysis for typical snowboarding backward falls.

Spinal injury (SPI) often causes death and disability in snow-sport accidents. SPIs often result from spinal compression and flexion, but the injury risks due to over flexion have not been studied. Back protectors are used to prevent SPIs but the testing standards do not evaluate the flexion-extension resistance. To investigate SPI risks and to better define back-protector specifications, this study quantified the flexion-extension range of motions (ROMs) of the thoracic-lumbar spine during typical snowboarding backward falls. A human facet-multibody model, which was calibrated against spinal flexion-extension responses and validated against vehicle-pedestrian impact and snowboarding backward fall, was used to reproduce typical snowboarding backward falls considering various initial conditions (initial velocity, slope steepness, body posture, angle of approach, anthropometry, and snow stiffness). The SPI risks were quantified by normalizing the numerical spinal flexion-extension ROMs against the corresponding ROM thresholds from literature. A high risk of SPI was found in most of the 324 accident scenarios. The thoracic segment T6-T7 had the highest injury risk and incidence. The thoracic spine was found more vulnerable than the lumbar spine. Larger anthropometries and higher initial velocities tended to increase SPI risks while bigger angles of approach helped to reduce the risks. SPIs can result from excessive spinal flexion-extension during snowboarding backward falls. Additional evaluation of back protector's flexion-extension resistance should be included in current testing standards. An ideal back protector should consider the vulnerable spinal segments, the snowboarder's skill level and anthropometry.

Cardiac MR Strain: A Noninvasive Biomarker of Fibrofatty Remodeling of the Left Atrial Myocardium.

Purpose To determine whether left atrial (LA) strain quantification with cardiac magnetic resonance (MR) imaging feature tracking is associated with the severity of LA fibrofatty myocardial remodeling at histologic analysis. Materials and Methods This prospective case-control study was approved by the institutional review board. LA strain was evaluated with cardiac MR feature tracking between January 2014 and March 2015 in 13 consecutive patients (mean age, 61 years ± 19; nine male) with mitral regurgitation in the 24 hours before mitral valve surgery and 13 age- and sex-matched healthy control subjects. LA strain parameters were compared first between control subjects and patients and then according to atrial fibrillation and mitral regurgitation status. Associations between LA strain and histology of preoperative biopsies were reported by using receiver operating characteristic curve analysis and Spearman correlation. Results Peak longitudinal atrial strain (PLAS) was significantly lower in patients with mitral regurgitation than in healthy control subjects (P < .001). Increased LA remodeling was significantly related to altered LA strain, and the strongest association was found between PLAS and the degree of fibrofatty myocardial replacement at histologic analysis (r = -0.75, P = .017). LA end-diastolic volume was increased in patients with mitral regurgitation when compared with that in healthy volunteers (P < .001) because of volume overload; however, volume did not correlate with the histologic degree of LA fibrofatty replacement (r = -0.35, P = .330). Conclusion LA strain, especially PLAS, correlates strongly with the degree of fibrofatty replacement at histologic analysis. Such functional imaging biomarker in combination with LA volumetry could help to guide clinical decisions, since myocardial structural remodeling is a known morphologic substrate of LA dysfunction leading to atrial fibrillation with adverse outcome. © RSNA, 2017 Online supplemental material is available for this article.

Characterization of Effective Orifice Areas of Mitral Prosthetic Heart Valves: An In-Vitro Study.

BACKGROUND: Reference values of hemodynamic parameters for the assessment of prosthetic heart valves are necessary, and ideally need to be provided by entities independent of the valve manufacturers. Thus, the study aim was to provide, in vitro, normal reference values of the effective orifice area (EOA) for different models and sizes of mitral prosthetic valve, and to assess the determinants of EOA and mean transvalvular pressure gradient (mTPG). METHODS: Four models of mechanical prostheses were tested (one mono-leaflet, three bi-leaflet) and four models of bioprostheses (two bovine pericardial, two porcine) on a double-activation pulsed duplicator that was specifically designed and optimized for assessing the hemodynamic performance of mitral prosthetic valves. The hemodynamic conditions were standardized and included for bioprostheses: two mitral flow volumes, three mean aortic pressures, two heart rates, and three E/A ratios. The EOAs were measured with Doppler echocardiography, using the same method (continuity equation) as was used in the clinical setting. Overestimation in term of EOA was defined according to guidelines as >0.25 cm2. RESULTS: EOA reference values were recorded. For mono-leaflet prostheses (Medtronic Hall 7700, size 25 to 31 mm) 2.29 and 3.49; for bi-leaflet prostheses (St. Jude Medical Master and Master HP, sizes 25 to 33 mm and On-X valve, sizes 27-29 mm) 1.34 and 4.74 cm2; for porcine bioprostheses (Medtronic Mosaic CINCH, sizes 25 to 31 mm and St. Jude Epic 100, sizes 25 to 33 mm) 1.35 and 3.56 cm2; for bovine pericardial bioprosthetic valves (Edwards Perimount 6900P and Magna Ease 7300, sizes 25 to 33 mm) 1.67 and 2.36 cm2. There were some discrepancies between the normal reference EOAs measured compared to those provided by the prosthesis manufacturers, or in published reports. The bioprosthetic EOAs were shown to be smaller than the manufacturers' values in 32% of valves (by an average of 0.57 ± 0.28 cm2) versus in 7% of valves when compared to values reported elsewhere (by an average of 0.43 ± 0.17 cm2). The relationship between EOA and internal orifice area (IOA) varied according to the type of prosthesis. The EOA was close to the IOA in mechanical valves (regression slopes 0.87-0.99) but was much smaller than the IOA in bioprosthetic valves (slopes 0.25-0.30). The EOA was influenced by prosthesis diameter, prosthesis stent diameter and height, while the mTPG was influenced by EOA and heart rate. CONCLUSIONS: The present study has provided normal reference values of EOAs for several frequently used mitral prostheses. This information may be helpful for identifying and quantifying prosthetic valve dysfunction and prosthesis-patient mismatch.

Left atrial aging: a cardiac magnetic resonance feature-tracking study.

Importance of left atrial (LA) phasic function evaluation is increasingly recognized for its incremental value in terms of prognosis and risk stratification. LA phasic deformation in the pathway of normal aging has been characterized using echocardiographic speckle tracking. However, no data are available regarding age-related variations using feature-racking (FT) techniques from standard cine magnetic resonance imaging (MRI). We studied 94 healthy adults (41 ± 14 yr, 47 women), who underwent MRI and Doppler echocardiography on the same day for left ventricular (LV) diastolic function evaluation. From cine MRI, longitudinal strain and strain rate, radial motion fraction, and radial relative velocity, respectively, corresponding to the reservoir, conduit, and LA contraction phases, were measured using dedicated FT software. Longitudinal strain and radial motion fraction decreased gradually and significantly with aging for both reservoir (r > 0.31, P < 0.003) and conduit (r > 0.54, P < 0.001) phases, whereas they remained unchanged during the LA contraction phase. Subsequently, the LA contraction-to-reservoir ratio increased significantly with age (r > 0.44, P < 0.001). Longitudinal strain rate and radial relative velocity significantly decreased with age (reservoir: r = 0.39, P < 0.001, conduit: r > 0.54, P < 0.001), and these associations tended to be stronger in women than in men. Finally, associations of LA functional indexes with age were stronger in individuals with lower transmitral early-to-atrial maximal velocity ratio and mitral annulus maximal longitudinal velocity, as well as higher transmitral early maximal-to-mitral annulus maximal longitudinal velocity ratio, highlighting the LV-LA interplay. Age-related changes in LA phasic function indexes were quantified by cine MRI images using a FT technique and were significantly related to age and LV diastolic function.

Impact of obesity and epicardial fat on early left atrial dysfunction assessed by cardiac MRI strain analysis.

BACKGROUND: Diastolic dysfunction is a major cause of morbidity in obese individuals. We aimed to assess the ability of magnetic resonance imaging (MRI) derived left atrial (LA) strain to detect early diastolic dysfunction in individuals with obesity and type 2 diabetes, and to explore the association between cardiac adipose tissue and LA function. METHODS: Twenty patients with obesity and T2D (55 ± 8 years) and nineteen healthy controls (48 ± 13 years) were imaged using cine steady state free precession and 2-point Dixon cardiovascular magnetic resonance. LA function was quantified using a feature tracking technique with definition of phasic longitudinal strain and strain rates, as well as radial motion fraction and radial velocities. RESULTS: Systolic left ventricular size and function were similar between the obesity and type 2 diabetes and control groups by MRI. All patients except four had normal diastolic assessment by echocardiography. In contrast, measures of LA function using magnetic resonance feature tracking were uniformly altered in the obesity and type 2 diabetes group only. Although there was no significant difference in intra-myocardial fat fraction, Dixon 3D epicardial fat volume(EFV) was significantly elevated in the obesity and type 2 diabetes versus control group (135 ± 31 vs. 90 ± 30 mL/m2, p < 0.001). There were significant correlations between LA functional indices and both BMI and EFV (p ≤ 0.007). CONCLUSIONS: LA MRI-strain may be a sensitive tool for the detection of early diastolic dysfunction in individuals with obesity and type 2 diabetes and correlated with BMI and epicardial fat supporting a possible association between adiposity and LA strain. Trials Registration Australian New Zealand Clinical Trials Registry No. ACTRN12613001069741.

Are the Current Doppler Echocardiography Criteria Able to Discriminate Mitral Bileaflet Mechanical Heart Valve Malfunction? An In Vitro Study.

Malfunction of bileaflet mechanical heart valves in the mitral position could either be due to patient-prosthesis mismatch (PPM) or leaflet obstruction. The aim of this article is to investigate the validity of current echocardiographic criteria used for diagnosis of mitral prosthesis malfunction, namely maximum velocity, mean transvalvular pressure gradient, effective orifice area, and Doppler velocity index. In vitro testing was performed on a double activation left heart duplicator. Both PPM and leaflet obstruction were investigated on a St. Jude Medical Master. PPM was studied by varying the St. Jude prosthesis size (21, 25, and 29 mm) and stroke volume (70 and 90 mL). Prosthesis leaflet obstruction was studied by partially or totally blocking the movement of one valve leaflet. Mitral flow conditions were altered in terms of E/A ratios (0.5, 1.0, and 1.5) to simulate physiologic panel of diastolic function. Maximum velocity, effective orifice area, and Doppler velocity index are shown to be insufficient to distinguish normal from malfunctioning St. Jude prostheses. Doppler velocity index and effective orifice area were 1.3 ± 0.49 and 1.83 ± 0.43 cm(2) for testing conditions with no malfunction below the 2.2 and 2 cm(2) thresholds (1.19 cm(2) for severe PPM and 1.23 cm(2) for fully blocked leaflet). The mean pressure gradient reached 5 mm Hg thresholds for several conditions of severe PPM only (6.9 mm Hg and mean maximum velocity value: 183.4 cm/s) whereas such value was never attained in the case of leaflet obstruction. In the case of leaflet obstruction, the maximum velocity averaged over the nine pulsed-wave Doppler locations increased by 38% for partial leaflet obstruction and 75% for a fully blocked leaflet when compared with normal conditions. Current echocardiographic criteria might be suboptimal for the detection of bileaflet mechanical heart valve malfunction. Further developments and investigations are required in order to further improve current guidelines.

Assessment of left atrial function by MRI myocardial feature tracking.

BACKGROUND: Left atrium (LA) volumes and function are predictors of cardiovascular events. Because LA function cannot be assessed from cardiovascular magnetic resonance imaging (MRI) using the well-established left ventricular tagging techniques, we hypothesized that adequate feature tracking (FT) applied to conventional cine MRI data could characterize LA function accurately. METHODS: We studied 10 young (28 ± 7 years) and 10 elderly (64 ± 6 years) healthy subjects, as well as 20 patients with moderate to severe aortic valve stenosis (AVS; 73 ± 15 years, effective aortic valve area: 0.67 ± 0.36 cm(2) ). MRI cine two-, three-, and four-chamber views were analyzed using a newly proposed FT method based on spatial correlation and endocardial detection resulting in: regional and global longitudinal strain and strain rate, radial motion fraction and relative velocity for the three LA motion phases including reservoir, conduit, and LA contraction. RESULTS: FT reliability was indicated by a good overlap between tracking results and manual LA endocardial borders, the low error for comparison against theoretical strains introduced in a synthetic phantom and the good inter-observer reproducibility (coefficient of variation < 15%). While all LA functional parameters were significantly impaired in AVS patients (p < 0.04), subclinical age-related variations induced a decreasing trend on all LA parameters but were significant only for radial conduit function parameters (p < 0.03). Finally, LA functional parameters characterized LA alteration in AVS with higher sensitivity than conventional LA volumetric parameters. CONCLUSIONS: Left atrial FT is feasible on MRI cine images and its addition to conventional analysis tools might enhance the diagnosis value of MRI in many heart diseases.

Assessment of the tolerance angle for pedicle screw insertion.

Cannulation process intervenes before implantation of pedicle screw and depends on the surgeon's experience. A reliable experimental protocol has been developed for the characterization of the slipping behavior of the surgical tool on the cortical shell simulated by synthetic materials. Three types of synthetic foam samples with three different densities were tested using an MTS Acumen 3 A/T electrodynamic device with a tri-axis 3 kN Kistler load cell mounted on a surgical tool, moving at a constant rotational speed of 10° mm-1 and performing a three-step cannulation test. Cannulation angle varied between 10° and 30°. Synthetic samples were scanned after each tests, and cannulation coefficient associated to each perforation section was computed. Reproducibility tests resulted in an ICC for Sawbone samples of 0.979 (p < 0.001) and of 0.909 (p < 0.001) for Creaplast and Sawbone samples. Cannulation coefficient and maximum force in Z-axis are found the best descriptors of the perforation. Angular threshold for perforation prediction was found to be 17.5° with an area under the curve of the Receiver Operating Characteristic of 89.5%. This protocol characterizes the cannulation process before pedicle screw insertion and identifies the perforation tool angle until which the surgical tool slips on the cortical shell depending on bone quality.

Morphological analysis of ventricular septal defect by echocardiography for prediction of aortic regurgitation in pediatric population.

Ventricular septal defects (VSD) are the most common congenital heart diseases in children. Among them, perimembranous VSD (pm-VSD) have a higher risk of complications, including aortic valve prolapse and aortic regurgitation (AR). The aim of our study was to assess echocardiographic criteria associated with AR during follow-up of pm-VSD. Forty children with restrictive pm-VSD, followed-up in our unit and who underwent a workable echocardiographic evaluation between 2015 and 2019 were included and retrospectively analyzed. The propensity score was used to match 15 patients with AR to 15 patients without AR. Median age was 2.2 year [1.4-5.7]. Median weight was 14 kg [9.9-20.3]. Aortic annulus z-score, Valsalva sinus z-score, sinotubular junction z-score, valve prolapse and commissure commitment were significantly different between the two groups (p = 0.047, p = 0.001, p = 0.010, p = 0.007, p < 0.001 respectively). Aortic root dilatation, aortic valve prolapse and commissure commitment to a perimembranous VSD are associated to aortic regurgitation.

Sliding on cortical shell: Biomechanical characterization of the vertebral cannulation for pedicle screw insertion.

BACKGROUND: Pedicular screws pull-out has been well studied unlike their insertion. A need for characterizing cannulation before pedicle screw implantation is highlighted in literature and offers promising prospects for future intra-operation instrumentation. A reliable cannulation protocol for ex-vivo testing in swine and cadaver vertebrae is presented in this work to predict extra pedicular perforation. METHODS: An MTS Acumen 3 A/T electrodynamic device, with a tri-axis 3 kN Kistler load cell mounted on a surgical tool was used to reproduce surgeon's gesture by moving at a constant rotational speed of 10°/mm and performing a three-section test. Perforation of the pedicle's cortical shell was planned through a design of experiment on the surgical tool angle at the entry point. Samples were scanned before and after mechanical tests and reproducibility of the protocol was tested on synthetic foam. Computation of the angle between cannulation tool and pedicle cortical shell was performed as well as cannulation coefficient of each perforation section. FINDINGS: A total of 68 pedicles were tested: 19 perforated and 21 non-perforated human pedicles, 17 perforated and 16 non-perforated swine pedicles. The reproducibility of the protocol for cannulation coefficient computation resulted in an intraclass correlation coefficient of 0.979. Cannulation coefficients results presented variability within spinal levels as well as between swine and human model. Correlation between bone density and cannulation coefficient was found significant (p < 0.005). Torque measurement was found to be the best predictor of perforation. Threshold of angle for prediction of perforation was found to be 21.7°. INTERPRETATION: Characterizing pedicle cannulation enables to predict extra pedicular perforation. Influence of bone mineral density and patient-specific morphology on pedicle cannulation has been highlighted together with a comparison of swine and cadaver models.

Traction mechanical characterization of porcine mitral valve annulus.

The Mitral Annulus (MA) is an anisotropic, fibrous, flexible and dynamical structure. While MA dynamics are well documented, its passive mechanical properties remain poorly investigated to complete the design of adequate prostheses. Mechanical properties in traction on four sections of the MA (aortic, left, posterior and right segments) were assessed using a traction test system with a 30 N load cell and pulling jaws for sample fixation. Samples were submitted to a 1.5 N pre-load, 10 pre-conditioning cycles. Three strain rates were tested (5 %/min, 7 %/min and 13 %/min), the first two up to 10 % strain and the last until rupture. High-resolution diffusion-MRI provided microstructural mapping of fractional anisotropy and mean diffusion within muscle and collagen fibres. Ten MA from porcine hearts were excised resulting in 40 tested samples, out of which 28 were frozen prior to testing. Freezing samples significantly increased Young Moduli for all strain rates. No significant differences were found between Young Moduli at different strain rates (fresh samples 2.4 ± 1.1 MPa, 3.8 ± 2.2 MPa and 3.1 ± 1.8 MPa for increasing strain rates in fresh samples), while significant differences were found when comparing aortic with posterior and posterior with lateral (p < 0.012). Aortic segments deformed the most (24.1 ± 9.4 %) while lateral segments endured the highest stress (>0.3 MPa), corresponding to higher collagen fraction (0.46) and fractional anisotropy. Passive machinal properties differed between aortic and lateral segments of the MA. The process of freezing samples altered their mechanical properties. Underlying microstructural differences could be linked to changes in strain response.

Experimental Bi-axial tensile tests of spinal meningeal tissues and constitutive models comparison.

Introduction This study aims at identifying mechanical characteristics under bi-axial loading conditions of extracted swine pia mater (PM) and dura and arachnoid complex (DAC). Methods 59 porcine spinal samples have been tested on a bi-axial experimental device with a pre-load of 0.01 N and a displacement rate of 0.05 mm·s-1. Post-processing analysis included an elastic modulus, as well as constitutive model identification for Ogden model, reduced Gasser Ogden Holzapfel (GOH) model, anisotropic GOH model, transverse isotropic and anisotropic Gasser models as well as a Mooney-Rivlin model including fiber strengthening for PM. Additionally, micro-structure of the tissue was investigated using a bi-photon microscopy. Results Linear elastic moduli of 108 ± 40 MPa were found for DAC longitudinal direction, 53 ± 32 MPa for DAC circumferential direction, with a significant difference between directions (p < 0.001). PM presented significantly higher longitudinal than circumferential elastic moduli (26 ± 13 MPa vs 13 ± 9 MPa, p < 0.001). Transversely isotropic and anisotropic Gasser models were the most suited models for DAC (r2  =  0.99 and RMSE:0.4 and 0.3 MPa) and PM (r2 = 1 and RMSE:0.06 and 0.07 MPa) modelling. Conclusion This work provides reference values for further quasi-static bi-axial studies, and is the first for PM. Collagen structures observed by two photon microscopy confirmed the use of anisotropic Gasser model for PM and the existence of fenestration. The results from anisotropic Gasser model analysis depicted the best fit to experimental data as per this protocol. Further investigations are required to allow the use of meningeal tissue mechanical behaviour in finite element modelling with respect to physiological applications. STATEMENT OF SIGNIFICANCE: This study is the first to present biaxial tensile test of pia mater as well as constitutive model comparisons for dura and arachnoid complex tissue based on such tests. Collagen structures observed by semi-quantitative analysis of two photon microscopy confirmed the use of anisotropic Gasser model for pia mater and existence of fenestration. While clear identification of fibre population was not possible in DAC, results from anisotropic Gasser model depicted better fitting on experimental data as per this protocol. Bi-axial mechanical testing allows quasi-static characterization under conditions closer to the physiological context and the results presented could be used for further simulations of physiology. Indeed, the inclusion of meningeal tissue in finite element models will allow more accurate and reliable numerical simulations.

Biomechanical comparison of spinal cord compression types occurring in Degenerative Cervical Myelopathy.

BACKGROUND: Degenerative Cervical Myelopathy results from spine degenerations narrowing the spinal canal and inducing cord compressions. Prognosis is challenging. This study aimed at simulating typical spinal cord compressions observed in patients with a realistic model to better understand pathogenesis for later prediction of patients' evolution. METHODS: A 30% reduction in cord cross-sectional area at C5-C6 was defined as myelopathy threshold based on Degenerative Cervical Myelopathy features from literature and MRI measurements in 20 patients. Four main compression types were extracted from MRIs and simulated with a comprehensive three-dimensional finite element spine model. Median diffuse, median focal and lateral types were modelled as disk herniation while circumferential type additionally involved ligamentum flavum hypertrophy. All stresses were quantified along inferior-superior axis, compression development and across atlas-defined spinal cord regions. FINDINGS: Anterior gray and white matter globally received the highest stress while lateral pathways were the least affected. Median diffuse compression induced the highest stresses. Circumferential type focused stresses in posterior gray matter. Along inferior-superior axis, those two types showed a peak of constraints at compression site while median focal and lateral types showed lower values but extending further. INTERPRETATION: Median diffuse type would be the most detrimental based on stress amplitude. Anterior regions would be the most at risk, except for circumferential type where posterior regions would be equally affected. In addition to applying constraints, ischemia could be a significant component explaining the early demyelination reported in lateral pathways. Moving towards patient-specific simulations, biomechanical models could become strong predictors for degenerative changes.

Tensile mechanical properties of the cervical, thoracic and lumbar porcine spinal meninges.

BACKGROUND: The spinal meninges play a mechanical protective role for the spinal cord. Better knowledge of the mechanical behavior of these tissues wrapping the cord is required to accurately model the stress and strain fields of the spinal cord during physiological or traumatic motions. Then, the mechanical properties of meninges along the spinal canal are not well documented. The aim of this study was to quantify the elastic meningeal mechanical properties along the porcine spinal cord in both the longitudinal direction and in the circumferential directions for the dura-arachnoid maters complex (DAC) and solely in the longitudinal direction for the pia mater. This analysis was completed in providing a range of isotropic hyperelastic coefficients to take into account the toe region. METHODS: Six complete spines (C0 - L5) were harvested from pigs (2-3 months) weighing 43±13 kg. The mechanical tests were performed within 12 h post mortem. A preload of 0.5 N was applied to the pia mater and of 2 N to the DAC samples, followed by 30 preconditioning cycles. Specimens were then loaded to failure at the same strain rate 0.2 mm/s (approximately 0.02/s, traction velocity/length of the sample) up to 12 mm of displacement. RESULTS: The following mean values were proposed for the elastic moduli of the spinal meninges. Longitudinal DAC elastic moduli: 22.4 MPa in cervical, 38.1 MPa in thoracic and 36.6 MPa in lumbar spinal levels; circumferential DAC elastic moduli: 20.6 MPa in cervical, 21.2 MPa in thoracic and 12.2 MPa in lumbar spinal levels; and longitudinal pia mater elastic moduli: 18.4 MPa in cervical, 17.2 MPa in thoracic and 19.6 MPa in lumbar spinal levels. DISCUSSION: The variety of mechanical properties of the spinal meninges suggests that it cannot be regarded as a homogenous structure along the whole length of the spinal cord.

Isometric osteopathic manipulation influences on cervical ranges of motion and correlation with osteopathic palpatory diagnosis: A randomized trial.

INTRODUCTION: Isometric manipulation is a current practice in osteopathy and treatment benefits have been reported in the literature. Such benefits could be assessed using experimental non-invasive cervical mobility measurements. The main objective was to quantitatively measure the effects of isometric manipulation on principal and compensatory cervical motions. METHODS: 101 healthy volunteers were included in this study. 51 healthy volunteers selected randomly underwent the experimental protocol before and after isometric treatment and were compared to 50 healthy volunteers who underwent a placebo treatment. Osteopathic diagnosis was performed on each healthy volunteer before and after the treatment. The experimental protocol included measurements by a motion capture system focusing on principal range of motion and compensatory motions. RESULTS: In both the isometric and the placebo sample, respectively including 51 (age: 29.2 ± 8.1, BMI: 22.2 ± 3.5) and 50 healthy volunteers (age: 27.4 ± 6.8, BMI: 22.9 ± 2.8), a pre-treatment diagnosis revealed a light cervical dysfunction in all subjects, mainly in levels C3 and C4. Altered ranges of motion thresholds (C3/C4 alterations) were identified: 113.2° for flexion, 130.0° for rotation and 90.2° for lateral flexion. After manipulations, the volunteers who underwent the isometric treatment presented a slight increase in amplitude for lateral flexion (p < 0.04), which was not found in the volunteers who underwent the placebo treatment. Compensatory motions showed differences pre and post isometric treatment without reaching significant values. CONCLUSION: Principal ranges of motion were found significantly higher after osteopathic treatment when compared to the placebo treatment. Osteopathic palpatory diagnosis showed significant correlation with range of motions before treatment.

Cervical Canal Morphology: Effects of Neck Flexion in Normal Condition: New Elements for Biomechanical Simulations and Surgical Management.

STUDY DESIGN: Continuous measurements and computation of absolute metrics of cervical subarachnoid space (CSS) and spinal cord (SC) geometries proposed are based on in vivo magnetic resonance imaging and 3D reconstruction. OBJECTIVE: The aim of the study is to offer a new methodology to continuously characterize and to quantify the detailed morphology of the CSS and the cervical SC in 3D for healthy subjects in both neutral supine and flexion. SUMMARY OF BACKGROUND DATA: To the best of our knowledge, no study provides a morphological quantification by absolute indices based on the 3D reconstruction of SC and CSS thanks to in vivo magnetic resonance imaging. Moreover, no study provides a continuous description of the geometries. METHODS: Absolute indices of SC (cross-sectional area, compression ratio, position in the canal, length) and of CSS (cross-sectional area, occupational ratio, lengths) were computed by measures from 3D semi-automatic reconstructions of high resolution in vivo magnetic resonance images (3D T2-SPACE sequence) on healthy subjects (N = 11) for two postures: supine neutral and flexion neck positions. The variability induced by the semi-automatic reconstruction and by the landmarks positioning were investigated by preliminary sensitivity analyses. Inter and intra-variability were also quantified on a randomly chosen part of our population (N = 5). RESULTS: The length and cross-sectional area of SC are significantly different (P < 0.05) in flexion compared with neutral neck position. Spinal cord stays centered in the canal for both postures. However, the cross-sectional area of CSS is submitted to low variation after C3 vertebra for both postures. Occupational ratio (OR) and compression ratio (CR) after C3 are significantly lower in flexion. CONCLUSION: This study presented interpretations of morphological measures: (1) left-right stability (described by the Left-Right eccentricity index) ensured by the denticulate ligaments and the nerve roots attached to the dural sheaths, (2) a Poisson effect of the SC was partially notified through its axial (antero-posterior [AP] diameter, OR, CR) and its longitudinal geometrical descriptions (length of spinal cord [LSC]). Such morphological data can be useful for geometrical finite element modeling and could now be used to compare with injured or symptomatic subjects. LEVEL OF EVIDENCE: 3.

Effect of experimental, morphological and mechanical factors on the murine spinal cord subjected to transverse contusion: A finite element study.

Finite element models combined with animal experimental models of spinal cord injury provides the opportunity for investigating the effects of the injury mechanism on the neural tissue deformation and the resulting tissue damage. Thus, we developed a finite element model of the mouse cervical spinal cord in order to investigate the effect of morphological, experimental and mechanical factors on the spinal cord mechanical behavior subjected to transverse contusion. The overall mechanical behavior of the model was validated with experimental data of unilateral cervical contusion in mice. The effects of the spinal cord material properties, diameter and curvature, and of the impactor position and inclination on the strain distribution were investigated in 8 spinal cord anatomical regions of interest for 98 configurations of the model. Pareto analysis revealed that the material properties had a significant effect (p<0.01) for all regions of interest of the spinal cord and was the most influential factor for 7 out of 8 regions. This highlighted the need for comprehensive mechanical characterization of the gray and white matter in order to develop effective models capable of predicting tissue deformation during spinal cord injuries.

Influence of the scale reduction in designing sockets for trans-tibial amputees.

The development of artificial prosthetic lower limbs aims to improve patient's mobility while avoiding secondary problems resulting from the use of the prostheses themselves. The residual limb is a pressure-sensitive area where skin injuries and pain are more likely to develop. Requirements for adequate prosthetic limbs have now become urgent to improve amputee's quality of life. This study aims to understand how socket design parameters related to geometry can influence pressure distribution in the residual limb. A finite element model was developed to simulate the mechanical loading applied on the residual limb of a below-knee amputee while walking. A sensitivity analysis to socket initial geometry, scaling the socket downward in the horizontal plane, was performed. Recordings include stress levels on the skin and in the residual limb deep soft tissues. Peak stress was reduced by up to 51% with a limited reduction of the socket size. More important scale reduction of the residual limb would lead to possible negative effects, such as stress concentrations in sensitive areas. This result confirms the interest of the prosthetist to develop a well-fitting socket, possibly a little smaller than the residual limb itself, in order to avoid residual limb mobility in the socket that could cause friction and stress concentrations. Non-homogeneous geometrical reductions of the socket should be further investigated.