Journal of biomechanics
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Journal of biomechanics · Jan 2008
The relation between intervertebral disc bulging and annular fiber associated strains for simple and complex loading.
Mechanical failure of the annulus fibrosus is mostly indicated by tears, fissures, protrusions or disc prolapses. Some of these annulus failures can be caused by a high intradiscal pressure. This has an effect on disc bulging. ⋯ Highest fiber associated strains were found to be located in small posterolateral regions. Fiber associated strains had a much higher magnitude than previously reported fiber associated strains. The results showed that combined loading is most likely to produce higher associated fiber strains compared to single axis loading.
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Journal of biomechanics · Jan 2008
A new technique for internal fixation of femoral fractures in mice: impact of stability on fracture healing.
Mouse models are of increasing interest to study the molecular aspects of fracture healing. Because biomechanical factors greatly influence the healing process, stable fixation of the fracture is of interest also in mouse models. Unlike in large animals, however, there is a lack of mouse models which provide stable osteosynthesis. ⋯ Of interest, the pin-clip fixation showed reliable union after 5 weeks, whereas the unstable pin fixation did not regularly achieve adequate fracture healing. In conclusion, we introduce a novel, easily applicable internal osteosynthesis technique in mice, which provides rotational stability after femoral fracture fixation. We further show that a more stable osteosynthesis significantly improves the process of fracture healing also in mice.
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Journal of biomechanics · Jan 2008
Computation of trunk equilibrium and stability in free flexion-extension movements at different velocities.
Velocity of movement has been suggested as a risk factor for low-back disorders. The effect of changes in velocity during unconstrained flexion-extension movements on muscle activations, spinal loads, base reaction forces and system stability was computed. In vivo measurements of kinematics and ground reaction forces were initially carried out on young asymptomatic subjects. ⋯ Some local lumbar muscles, especially in subjects with larger lumbar flexion and at slower paces, also demonstrated flexion relaxation. Results confirmed the crucial role of movement velocity on spinal biomechanics. Predictions also demonstrated the important role on response of the magnitude of peak lumbar rotation and its temporal variation.
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Journal of biomechanics · Jan 2008
Vertebral end-plate fractures as a result of high rate pressure loading in the nucleus of the young adult porcine spine.
In a healthy spine, end-plate fractures occur from excessive pressurization of the intervening nucleus. Younger spines are most susceptible to such type of injury due to the highly hydraulic nature of their intervertebral discs. The purpose of this paper was to confirm this fracture mechanism of the healthy spine through the pressurization of the nucleus in the absence of external compressive loading. ⋯ Also, in each of the growth-plate fractured specimens, nuclear material was forcefully emitted, during fracture, from the intervertebral disc into the vertebral foramen. The posterior end-plate fractures produced here are similar to those often seen in young adult humans. This provides insight into a mechanism of fracture development through pressurization of the nucleus that might be seen in older adolescents and younger adults during athletic events or mild trauma.
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Journal of biomechanics · Jan 2007
Three-dimensional inhomogeneous triphasic finite-element analysis of physical signals and solute transport in human intervertebral disc under axial compression.
A 3D inhomogeneous finite-element model for charged hydrated soft tissues containing charged/uncharged solutes was developed and applied to analyze the mechanical, chemical, and electrical signals within the human intervertebral disc during an axial unconfined compression. The effects of tissue properties and boundary conditions on the physical signals and the transport of fluid and solute were investigated. The numerical simulation showed that, during disc compression, the fluid pressurization and the effective (von Misses) solid stress were more pronounced in the annulus fibrosus (AF) region near the interface between AF and nucleus pulposus (NP). ⋯ The electrical signals were very sensitive to fixed charge density. Changes in material properties of NP (water content, fixed charge density, and modulus) affected fluid pressure, electrical potential, effective stress, and solute transport in the disc. This study is important for understanding disc biomechanics, disc nutrition, and disc mechanobiology.