A comparison of rigid, semi-rigid and flexible spinal stabilization devices: A finite element study

Abstract

Pedicle-screw-based spinal fixation system has shown its success for treating degenerative disc disease-related back pain and spinal instability. In the last few decades, several non-fusion implants ( ‘flexible’ or ‘dynamic’ fixation) are developed for treating slight degenerate disc disease. The aim of this study is to characterize and compare the biomechanical responses of pedicle-screw-based fusion with various rod materials and a flexible spinal stabilization device on the lumbar spine (L3L5). Computed tomography scan-based finite element model and pedicle screw fixation with rigid rod material stainless steel rod, semi-rigid rod material poly-ether-ether-ketone and flexible rod device made of stainless steel are used in this study. Intact model of the lumbar spine and treated with all the different implants are simulated under typical physiological loading conditions. Compared with the intact model, pedicle screw with the stainless steel rod fixation system is found to offer very less range of motion. Poly-ether-ether-ketone rod system increased range of motion 3.8, 7 and 1.8 times for axial rotation, lateral bending and flexion–extension, respectively, compared to the stainless steel rod system. The flexible rod device rod system is found to reduce stress on vertebral body, carrying out more loads as compared to poly-ether-ether-ketone rods. In the case of stainless steel rods, range of motion is almost restricted on the fusion zone, which is overcome by the poly-ether-ether-ketone rod system to some extent and farther improved by the flexible rod device rod system. So, the poly-ether-ether-ketone rod and flexible rod device rod systems may be implemented for better clinical results after succeeding experimental validation and clinical trial.

Biomechanical properties of a novel nonfusion artificial vertebral body for anterior lumbar vertebra resection and internal fixation

“…This is consistent with our previous results from in vitro mechanics tests on fresh cadaver specimens 11 . It was suggested that fusion surgery would seriously affect the physiological motor function of the lumbar spine at the surgical site and increase the intervertebral disc ROM in the adjacent segments, which was consistent with the previous research results of Biswas, JK et al 21 . Although the ROMs of the adjacent discs to the surgical site were reduced in the nonfusion group compared with those in the intact group, the difference between the two groups was not obvious.…”

Hybrid surgery with PEEK rods for lumbar degenerative diseases: a 2-year follow-up study

“…Although both types of rods can significantly reduce the mobility of the fixed segment (> 70%), PEEK rods can provide greater all-directional mobility than can titanium rods [ 20 – 22 ]. The finite element analysis showed that compared with titanium rods, PEEK rods can increase the range of flexion and extension, lateral flexion and axial rotation by 1.8-2.1, 7-7.2 and 3.7-3.8 times, respectively [ 23 , 24 ]. Biswas et al [ 24 ] performed finite element analysis and reported that the mobility of the fixed segment of PEEK rods was 4.2°-6.2° in flexion and 4.2°-1.1° in extension.…”

Design and development of a novel expanding flexible rod device (FRD) for stability in the lumbar spine: A finite-element study

“…To simulate physiological flexion, extension, lateral bending and axial rotational motions, 2, 4, 6, 8 and 10 Nm bending moment are applied on L1 vertebrae to implanted (FRD) and intact (natural) models. 20…”

“…To simulate physiological flexion, extension, lateral bending and axial rotational motions, 2, 4, 6, 8 and 10 Nm bending moment are applied on L1 vertebrae to implanted (FRD) and intact (natural) models. 20 Multilinear stress-strain curve Ligaments [16][17][18] Young's modulus (MPa) Poisson's ratio Anterior longitudinal ligament (ALL) 7.8 (ε < 12%) 20 (ε > 12%) 0.3 Posterior longitudinal ligament (PLL)…”