Influence of Whole-Body Vibration on Dynamic Response of Lumbar Spine after Transformal Lumbar Interbody Fusion

Introduction: Occupational whole body vibration (WBV) plays a major role in determining dynamic responses of the lumbar spine. WBV has been shown to cause low-back problems and degenerative disc diseases. Fusion surgery such as trans-formal lumbar inter-body fusion (TLIF) have been widely utilized to treat such disorders. Materials and Methods: In this study, finite element method (FEM) was used to investigate dynamic responses of the lumbar spine due to WBV with the frequency in the range of regular physiologic activities after TLIF. A FE model of the L1-L5 lumbar spine was modeled and cyclic loading with the frequency of 1 Hz and 5 Hz were exerted to the model. Then, the disc bulge and stress distribution on the annual ground substance and vertebral bodies were measured.Results: It was observed that the maximum disc bulge (MDB) and maximum von-Mises stress (MMS) occurred in proportion to the loading frequency; overall, in the 5 Hz model, MDB and MMS were detected to happen 5 times more frequently as compared to the 1 Hz model. However, the magnitude of MDB and MMS were not generally affected by the loading frequency. Conclusions: It can be concluded that different frequency of WBV, although in the physiologic range, can alter dynamic responses of the lumbar spine and, thus, their fatigue behavior. In the results can be of assistance to broaden the understanding regarding the dynamic responses of the lumbar spine during WBV after TLIF

Mechanical Vulnerability of L3-L4 Spinal Segment after Fusion Surgery Utilizing Dynamic Stress Analysis

Introduction: Pedicle screw-based spine fusion has been employed as a felicitous approach for treatment of degenerative lumbar spinal diseases.  Although the pedicle screw designs and fixation techniques have progressed, many clinical studies have reported the adjacent segment degeneration (ASD) and several other adverse effects after surgery. In the case of fixation techniques, the use of semi-rigid rods such as Polyarylether ether ketone (PEEK) rods can be an appropriate substitute for rigid fusion instrumentation. However, the biomechanical effects of using viscoelastic PEEK rods for use in clinical studies are still unclear. Materials and Methods: In this study, the effects of using two pedicle screw-based stabilization systems, i.e. viscoelastic PEEK rods and elastic Titanium rods, on the stress distribution in L3-L4 intervertebral disc and the surrounding osseous tissue were investigated. An L1-L5 lumbar region was modeled. Subsequently, a mild degenerative disc disease was simulated in the L3-L4 lumbar level. Next, an axial cyclic torque was applied to the model.Results: The results showed that, at the end of the loading cycle, the maximum von-Mises stress in the L3-L4 intervertebral disc as well as the overall value of stress in the surrounding osseous tissue were slightly greater in the viscoelastic model as compared to the elastic one. Nonetheless, the stress distribution contours and the location of maximum stress were different in the two models. Conclusion: It can be postulated that the vulnerable areas of lumbar bone are different in two models