Journal of biomechanical engineering
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Disc degeneration, usually associated with low back pain and changes of intervertebral stiffness, represents a major health issue. As the intervertebral disc (IVD) morphology influences its stiffness, the link between mechanical properties and degenerative grade is partially lost without an efficient normalization of the stiffness with respect to the morphology. Moreover, although the behavior of soft tissues is highly nonlinear, only linear normalization protocols have been defined so far for the disc stiffness. ⋯ Therefore, the larger CV after normalization can be interpreted as a strong variability of the material properties, previously hidden by the geometry's own influence. In conclusion, a new normalization protocol for the intervertebral disc stiffness in compression, flexion, extension, bilateral torsion and bending was proposed, with the possible use of MRI and FE to acquire the discs' anatomy and determine the nonlinear relations between stiffness and morphology. Such protocol may be useful to relate the disc's mechanical properties to its degree of degeneration.
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Currently, rigid fixation systems are the gold standard for degenerative disk disease treatment. Dynamic fixation systems have been proposed as alternatives for the treatment of a variety of spinal disorders. These systems address the main drawbacks of traditional rigid fixation systems, such as adjacent segment degeneration and instrumentation failure. ⋯ In extension, the facet load in DSDR case was similar to that in intact spine. The dynamic rod constructions (DSDR and RSDR) led to a lesser peak stress at screws compared with rigid rod constructions (DSRR and RSRR) in all loading cases. A dynamic construct consisting of a dynamic rod and a dynamic screw did protect the adjacent level from excessive motion.
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Joint injuries and the resulting posttraumatic osteoarthritis (OA) are a significant problem. There is still a need for tools to evaluate joint injuries, their effect on joint mechanics, and the relationship between altered mechanics and OA. Better understanding of injuries and their relationship to OA may aid in the development or refinement of treatment methods. ⋯ The SCM technique was able to evaluate variations in contact outcomes arising from scapholunate ligament injury and also the effects of surgical repair, with similar accuracy to the FEM gold standard. At least 80% of contact forces, peak contact pressures, mean contact pressures and contact areas from SCM were within 10 N, 0.5 MPa, 0.2 MPa, and 15 mm2, respectively, of the results from FEM, regardless of the state of the wrist. Depending on the application, the MRI-based SCM technique has the potential to provide clinically relevant subject-specific results in a computationally efficient manner compared to FEM.
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The bicuspid aortic valve (BAV), which forms with two leaflets instead of three as in the normal tricuspid aortic valve (TAV), is associated with a spectrum of secondary valvulopathies and aortopathies potentially triggered by hemodynamic abnormalities. While studies have demonstrated an intrinsic degree of stenosis and the existence of a skewed orifice jet in the BAV, the impact of those abnormalities on BAV hemodynamic performance and energy loss has not been examined. This steady-flow study presents the comparative in vitro assessment of the flow field and energy loss in a TAV and type-I BAV under normal and simulated calcified states. ⋯ The presence of simulated calcific lesions normalized the alignment of the BAV jet and resulted in the loss of jet axisymmetry in the TAV. It also amplified the degree of stenosis in the TAV and BAV, as indicated by the 342% and 404% increase in EL, 70% and 51% reduction in ELI and 48% and 51% decrease in EOA, respectively, relative to the nontreated valve models at the maximum flow rate. This study indicates the ability of the BAV to function as a TAV despite its intrinsic degree of stenosis and suggests the weak dependence of pressure drop on orifice area in calcified valves.
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Bone sawing is widely used in orthognathic surgery to correct maxillary deformities. Successful execution of bone sawing requires a high level of dexterity and experience. A virtual reality (VR) surgical simulator can provide a safe, cost-effective, and repeatable training method. ⋯ By performing multiple regression analysis, the prediction models for the bone-sawing procedure were determined. By employing Omega.6 as a haptic device, a medical simulator for the Lefort I osteotomy was developed based on an experimental force model. Comparison of the force-time curve acquired through experiments and the curve computed from the simulator indicate that the obtained forces based on the experimental force model and the acquired data had the same trend for the bone-sawing procedure of orthognathic surgery.