Material properties of bovine intervertebral discs across strain rates

AbstractThe intervertebral disc (IVD) is a complex structure responsible for distributing compressive loading to adjacent vertebrae and allowing the vertebral column to bend and twist. To study the mechanical behaviour of individual components of the IVD, it is common for specimens to be dissected away from their surrounding tissues for mechanical testing. However, disrupting the continuity of the IVD to obtain material properties of each component separately may result in erroneous values. In this study, an inverse finite element (FE) modelling optimisation algorithm has been used to obtain material properties of the IVD across strain rates, therefore bypassing the need to harvest individual samples of each component. Uniaxial compression was applied to ten fresh-frozen bovine intervertebral discs at strain rates of 10-3–1/s. The experimental data were fed into the inverse FE optimisation algorithm and each experiment was simulated using the subject specific FE model of the respective specimen. A sensitivity analysis revealed that the IVD's response was most dependent upon the Young's modulus (YM) of the fibre bundles and therefore this was chosen to be the parameter to optimise. Based on the obtained YM values for each test corresponding to a different strain rate (ε̇), the following relationship was derived:YM=35.5lnε̇+527.5. These properties can be used in finite element models of the IVD that aim to simulate spinal biomechanics across loading rates

Injury risk of interphalangeal and metacarpophalangeal joints under impact loading

Injuries to the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of the hand are particularly disabling. However, current standards for hand protection from blunt impact are not based on quantitative measures of the likelihood of damage to the tissues. The aim of this study was to evaluate the probability of injury of the MCP and PIP joints of the human hand due to blunt impact. Impact testing was conducted on 21 fresh-frozen cadaveric hands. Unconstrained motion at every joint was allowed. All hands were imaged with computed tomography and dissected post-impact to quantify injury. An injury-risk curve was developed for each joint using a Weibull distribution with dorsal impact force as the predictive variable. The injury risks for PIP joints were similar, as were those for MCP joints. The risk of injury of the MCP joints from a given applied force was significantly greater than that of the PIP joints (p = 0.0006). The axial forces with a 50% injury risk for the MCP and PIP joints were 3.0 and 4.2 kN, respectively. This is the first study to have investigated the injury tolerance of the MCP and PIP joints. The proposed injury curves can be used for assessing the likelihood of tissue damage, for designing targeted protective solutions such as gloves, and for developing more biofidelic standards for assessing these solutions.status: publishe

Material properties of bovine intervertebral discs across strain rates - dataset

<p>Raw experimental data from axial compression tests of each of the bovine intervertebral disc specimens and the .dat files from each of the subject specific FE models at each strain rate.</p

Mapping the Risk of Fracture of the Tibia From Penetrating Fragments.

Penetrating injuries are commonly inflicted in attacks with explosive devices. The extremities, and especially the leg, are the most commonly affected body areas, presenting high risk of infection, slow recovery, and threat of amputation. The aim of this study was to quantify the risk of fracture to the anteromedial, posterior, and lateral aspects of the tibia from a metal fragment-simulating projectile (FSP). A gas gun system and a 0.78-g cylindrical FSP were employed to perform tests on an ovine tibia model. The results from the animal study were subsequently scaled to obtain fracture-risk curves for the human tibia using the cortical thickness ratio. The thickness of the surrounding soft tissue was also taken into account when assessing fracture risk. The lateral cortex of the tibia was found to be most susceptible to fracture, whose impact velocity at 50% risk of EF1+, EF2+, EF3+, and EF4+ fracture types - according to the modified Winquist-Hansen classification - were 174, 190, 212, and 282 m/s, respectively. The findings of this study will be used to increase the fidelity of predictive models of projectile penetration

The effect of high tibial osteotomy on stress in the tibio-femoral joint: a computer simulation study

Osteoarthritis (OA) is a degenerative disease of all of the tissues within the diarthrodial joint and one of the leading causes of disability. Knee OA is often caused by lower limb malalignment, high body mass index, and injury to the surrounding soft tissues, resulting in a cyclic degradation of the joint. High tibial osteotomy (HTO) is a realignment surgery to restore knee function and minimise excessive loading. However, the link between malalignment and stress in the knee is not well understood and surgical outcomes by HTO have been unpredictable. Therefore the overarching goal is to develop a three-dimensional virtual surgery finite element (FE) model that integrates subject specific imaging and computational biomechanics to predict the effects of different realignment techniques on knee joint contact stress. FE models of a cadaveric knee joint were created from magnetic resonance images, using Mimics v14 (Materialise, Belgium). Following non-manifold assembly, these 3D models were exported to Abaqus 6.11 to determine the stress distribution within the medial-lateral compartments of the well-aligned knee. A 10° open wedge HTO was performed to simulate the malaligned knee. Boundary conditions of 300N axial load and 12 Nm bending moment were applied to simulate posture in the well aligned and malaligned knee. Peak compressive stress in the malaligned knee was 60% higher than that of the well-aligned knee. This excessive stress is considered a primary factor for the onset and progression of OA. These results highlight the importance of understanding the effects of HTO on the knee joint contact stresses in order to delay OA progression

Knee joint contact mechanics in a malaligned limb: an integrated finite element and in vitro study

Excessive joint stress, often caused by knee malalignment, contributes to osteoarthritis (OA) progression. High tibial osteotomy (HTO) is a conservative surgery that corrects lower limb malalignment to relieve damaged tissues from excessive loading. However, HTO outcome has been highly variable and the relationship between the degree of malalignment correction and knee joint contact stresses is not known. If this were known, HTO could be tailored to each patient to best restore joint stresses to normal levels. Therefore, the aim of this work is to create a three-dimensional (3D) finite element (FE) model of the knee joint to predict the effect of different malalignment corrections on knee joint contact stresses. In this study, we present the verification of our subject-specific 3D FE model