Stress distribution of different lumbar posterior pedicle screw insertion techniques: a combination study of finite element analysis and biomechanical test

Abstract

At present, the pedicle screw is the most commonly used internal fixation device. However, there are many kinds of common posterior pedicle screw insertion techniques performed to reconstruct the lumbar stability. Therefore, spinal surgeons often face a difficult choice. The stress distribution of internal fixation system is an important index for evaluating safety. Unfortunately, little had been known about the difference of stress distribution of screw-rod systems that established by Roy-Camille, Magerl and Krag insertion techniques. Here, combination of finite element analysis and model measurement research was adopted to evaluate the difference of stress. Following different pedicle screw insertion techniques, three lumbar posterior surgery models were established after modeling and validation of the L1–S1 vertebrae finite element model. By analyzing the data, we found that stress concentration phenomenon was in all the postoperative models. Roy-Camille and Magerl insertion techniques led to the great stress on screw-rod systems. Then, fresh frozen calf spines were selected as a model for subsequent measurements. Fitted with a specially designed test pedicle screw, L5–L6 vertebrae were selected to repeat and verify the results of the finite element analysis. With the aid of universal testing machine and digital torque wrench, models simulated flexion, extension, lateral bending and rotation. Finally, the strain value was captured by the strain gauge and was then calculated as the stress value. Krag and Magerl were found to be the safer choice for pedicle screw insertion. Overall, our combination method obtained the reliable result that Krag insertion technique was the safer approach for pedicle screw implantation due to its relatively dispersive stress. Therefore, without the consideration of screw size, pedicle fill, bone density, and bone structures, we recommend the Krag insertion technique as the first choice to reconstruction of lumbar stability. Additionally, the combination method of finite element analysis and strain gauge measurement can provide a feasible way to study the stress distribution of spinal internal fixation.

Biomechanical evaluation of a short-rod technique for lumbar fixation surgery

“…Fragmentation of the CSSR region has been reported in the literature. A screw-rod system like the “crane” force structure determines the stress concentration at the center of rotation, where the screw and rod come into contact ( Song et al, 2021 ). In addition to the stress on the pedicle screw, the insertion method and stability of the screw fixation system can also have a considerable effect on the healing capacity of the injured vertebra.…”

“…The volume ratio of the annulus fibrosus and nucleus pulposus was 3:7 ( Goto et al, 2002 ). The cortical bone was 1 mm thick, and the endplates on the upper and lower surface of the vertebrae simulated the connection between the vertebrae and the intervertebral disc ( Song et al, 2021 ). The thickness of the cartilage layer of the facet joint was assumed to be 0.2 mm ( Kim et al, 2015 ).…”

“…To validate the FE model, the L4–L5 intervertebral disc was subjected to pure compressive forces of 150, 400, and 1000 N, and the resulting stresses were compared with in vitro experimental data ( Brinckmann and Grootenboer, 1991 ; Dreischarf et al, 2014 ). Considering the limitations on exercise postoperatively, the model was also placed under a 300 N axial ( Song et al, 2021 ) and three different moments (3.0, 7.5, and 10 Nm) to simulate flexion, extension, lateral bending, and axial rotation. The resulting range of motion (ROM) of L4–L5 was compared with in vivo experimental results ( Goel et al, 1985 ; Yamamoto et al, 1989 ; Karahalios et al, 2010 ).…”

Unilateral pedicle screw fixation of lumber spine: A safe internal fixation method

“…We established a model of L3-S1 based on a previous FE model of the total lumbar spine [ 23 ]. The CT scanning layer thickness was 0.625 mm.…”

Biomechanical effects of individualized artificial titanium alloy lamina implantation after laminectomy: A finite element analysis

“…In the first step, a vertical axial preload of 500 N was applied to the upper surface of L1 as a representation of the upper body weight and muscle forces. In the second step, a 10 N-m moment was applied to the top center of the L1 vertebral body to simulate four movements of flexion, extension, lateral bending, and axial rotation for clinical prediction ( Biswas et al, 2018 ; Song et al, 2021 ).…”