Papers of the Year
Nonlinear mechanical analysis of posterior spinal instrumentation for osteoporotic vertebra: Effects of mechanical properties of the rod on the failure risks around the screw
- Release Date :
In spinal fusion with instrumentation for the treatment of osteoporotic vertebral fracture, it is common for pedicle screws, which are inserted into vertebrae and strongly immobilized by a rigid rod, to loosen and dissociate. One of their expected causes is failure and reduction of fixity around a screw. An improved rod with a damper structure has thus been proposed to increase the freedom of movement of the rod and allow more flexible fixation of the spine. To evaluate the availability of the proposed structure and establish appropriate improved design of screws and rods with fewer occurrences of loosening and dissociation, effects of the structural change to the improved rod on the distribution of failure risks around the screw need to be investigated. In the present study, we performed nonlinear fracture analysis for spinal instrumentation surgery using an osteoporosis model and evaluated the failure distribution in the vertebrae while changing the apparent stiffness of the damper joint. Our finite element analysis showed that there were few expected failures in the flexible fixation model, indicating the effectiveness of the improved structure of the rod in reducing the loosening and dissociation of screws. It also suggested that the reduction was derived from the allowance of horizontal deformation in the damper joint in the improved rod. The potential of the structural improvement and the mechanism responsible for reducing the risks of loosening and dissociation are discussed.
- Orthopedic computational biomechanics, Spinal instrumentation, Non-linear analysis, Loosening of screw, Osteoporosis
- Paper information
- Daisuke TAWARA, Kenta NORO, Tetsuya TSUJIKAMI, Yoshiyuki OKAMOTO and Hideki MURAKAMI, “Nonlinear mechanical analysis of posterior spinal instrumentation for osteoporotic vertebra: Effects of mechanical properties of the rod on the failure risks around the screw”, Journal of Biomechanical Science and Engineering, Vol.9, No.2 (2014), p.13-00163. doi:10.1299/jbse.13-00163. Final Version Released on December 15, 2014, Advance Publication Released on June 30, 2014.
Numerical analysis of arterial contraction regulated by smooth muscle stretch and intracellular calcium ion concentration
In this study, for a better understanding of arterial functions, we examine the effects of active stresses, which are generated by contractile units included in smooth muscle cells, on the stress distribution in the arterial wall. Thus far, it is widely recognized that active stress generation is regulated by mechanical and chemical operations, i.e., both smooth muscle stretch and intracellular calcium ion concentration. Based on this fact, we develop an arterial wall model with active stresses that couples the mechanical and chemical ones suitable for the finite element method. By using this coupled model within the framework of finite element analysis, we calculate the stress distribution including active stresses at a prescribed intracellular calcium ion concentration. The results show that as the intracellular calcium ion concentration increases, the effect of active stress appears continuously, i.e., stress distribution could be considered as a continuous function of the intracellular calcium ion concentration. To obtain stress distributions at the prescribed intracellular calcium ion concentration, which is assumed to be reached as a result of active calcium ion transport under various in vivo conditions, are meaningful as a preliminary step in developing advanced models considering the active calcium ion transport systems.
- Artery, Active stress, Mechanochemical model, Intracellular calcium ion concentration, Smooth muscle stretch, Nonlinear finite element method
- Paper information
- Naoki KIDA and Taiji ADACHI, “Numerical analysis of arterial contraction regulated by smooth muscle stretch and intracellular calcium ion concentration”, Journal of Biomechanical Science and Engineering, Vol.9, No.1 (2014), p.JBSE0002. doi:10.1299/jbse.2014jbse0002