Analysis of Compression Behavior on Intervertebral Disc L4-5 in Pedicle Screw System Instrumented Lumbar Spine under Follower Load / 영남의대학술지

BACKGROUND: Confirm the stability of intervertebral disc sustaining each fused lumbar spine cases, comparing vertical compression, A-P shear force and rotational moment on intervertebral disc of instrumented lumbar spine with simple vertical compression load and follower load using finite element analysis. MATERIALS AND METHODS: We analyze the stability of intervertebral disc L4-5 supporting fused lumbar spine segments. After performing finite element modelling about L1-L5 lumbar vertebral column and L1-L4 each fusion level pedicle screw system for fused lumbar spine fine element model. Intervertebral discs with complex structure and mechanical properties was modeled using spring element that compensate stiffness and tube-to-tube contact element was employed to give follower load. Performing geometrical non-linear analysis. RESULTS: The differences of intervertebral disc L4-5 behavior under the follower compression load in comparision with vertical compression load are as follows. CONCLUSION: As a result of finite element interpretation of instrumented lumbar spine, the stability of L4-5 sustaining fused lumbar segment, the long level fused lumbar spine observed hing stability under follower load. This research method can be the basis tool of effects prediction for instrumentation, a invention of a more precious finite element interpretation model which consider the role of muscle around the spine is loaded.

Analysis of Compression Behavior on Intervertebral Disc L4-5 in Pedicle Screw System Instrumented Lumbar Spine under Follower Load / 영남의대학술지

BACKGROUND: Confirm the stability of intervertebral disc sustaining each fused lumbar spine cases, comparing vertical compression, A-P shear force and rotational moment on intervertebral disc of instrumented lumbar spine with simple vertical compression load and follower load using finite element analysis. MATERIALS AND METHODS: We analyze the stability of intervertebral disc L4-5 supporting fused lumbar spine segments. After performing finite element modelling about L1-L5 lumbar vertebral column and L1-L4 each fusion level pedicle screw system for fused lumbar spine fine element model. Intervertebral discs with complex structure and mechanical properties was modeled using spring element that compensate stiffness and tube-to-tube contact element was employed to give follower load. Performing geometrical non-linear analysis. RESULTS: The differences of intervertebral disc L4-5 behavior under the follower compression load in comparision with vertical compression load are as follows. CONCLUSION: As a result of finite element interpretation of instrumented lumbar spine, the stability of L4-5 sustaining fused lumbar segment, the long level fused lumbar spine observed hing stability under follower load. This research method can be the basis tool of effects prediction for instrumentation, a invention of a more precious finite element interpretation model which consider the role of muscle around the spine is loaded.

Effect of Insertion Status of a Pedicular Screw on its Mechanical Properties using the Finite Element Method / 대한정형외과학회잡지

PURPOSE: The structural performance of a fixation system was investigated in the case of screw insertion into the pedicular canal with or without its threads fastened in the cortex and in the broken pedicle. MATERIALS AND METHODS: The symmetric geometric model was used for the pull-out test, and the simplified 3-dimensional model at 3 level, namely, the 3rd, 4th and 5th lumbar vertebrae, was used for the axial compressive loading test. RESULTS: According to the result of the axial-loading test, bending moments and Von-Mises stresses were increased at the junction between the head and the 2nd and 3rd pitches of the lumbar pedicle screw and at the center of 4th lumbar vertebral body, in the models of intact, posterior elements removed and unstable fractured spines. As the results of flexibility, there is no difference in intra-cortical insertion compared to intra-medullary pedicle insertion in the intact spine model. However, flexibility of the laminectomy model was 8% better that of the intra-cortical insertion, and the unstable fracture model 2% better. CONCLUSION: There is no difference in the flexibility of intra-cortical and intra-medullary pedicle screw insertion. The stability of the posterior structure is more important than anterior pedicle screw fixation.

Analysis of Compression Behavior in Lumbar Spine Under Simple Vertical Load vs Follower Load / 대한척추외과학회지

PURPOSE: To clarify the behavior of the lumbar spine under vertical compressive load and follower compressive load and to confirm the effect of the follower load on the stability of the spinal column using finite element method. MATERIALS AND METHODS: Describing follower compression test to overcome underestimation of load carrying capacity, the problem in existing ex-vivo lumbar spine compression test, with finite element analysis, comparing with the result of simple vertical compressive load, we analyze the property of kinetic behavior. After performing finite element modelling about L1-L5 lumbar vertebral column, analyze it about vertical compressive load and follower compressive load. Intervertebral discs with complex structure and mechanical properties was modeled using spring element that compensate stiffness and tube-to-tube contact element was employed to give follower load. With compressive load, change of lumbar spinal curve is so much, that geometrical analysis should be done. RESULTS: Under the follower compressive load, the vertebral column was so stiff that vertical displacement of the upper end plate of L1 was markedly reduced, comparing with that under the simple vertical compressive load. Sagittal rotation of that upper end plate was also decreased in the opposite direction. Compressive load on the intervertebral disc was evenly distributed along the entire column. The bending moment at each disc was reduced in the opposite direction. A lesser A-P shear force occurred at the intervertebral disc. CONCLUSION: As a result of finite element interpretation of lumbar spine, the stability and load carrying capacity was increased largely, and the compressive load was transmitted through the column in a more pattern, when follower compressive load applied. This can provide the basis for explaining the difference of early buckling occurrence reported in ex-vivo testing, and load carrying capacity of the lumbar spine in-vivo, but, for more precise replication of behavior of lumbar spine in-vivo to variable loading. A invention of a more precious finite element interpretation model which consider the role of muscle around the spine is loaded.