Finite Element Analysis of 3 Posterior Fixation Techniques in the Lumbar Spine

Abstract

This study compared the biomechanics of 3 fixation techniques: bilateral pedicle screw (BPS) fixation, unilateral pedicle screw (UPS) fixation, and UPS supplemented with translaminar facet screw (UPS+TLFS) fixation. The study was conducted in an L3-L5 finite element model. Three different finite element models were created by adopting different fixation techniques after removal of the left L3-L4 and L4-L5 facet joints. A 500-N compressive preload combined with 8-NM moment were applied in 3 finite element models with 3 fixation techniques during different movements. Angular displacement and stress distribution were recorded. As described in this article, the UPS model had the most variation in angular displacement, the BPS model was intermediate, and the UPS+TLFS model had the least mobility. Most of the stress accumulated on the body and tail of the pedicle screws and the connecting rods in the UPS and BPS models, but stress accumulated on the rods and the part of the facet joint pierced by the TLFS in the UPS+TLFS model. The middle part of the pedicle screw endured little stress compared with the upper and lower parts. The maximum stress on the fixation devices was highest in the UPS model. The maximum stress in the UPS+TLFS model was the lowest among the 3 models. Biomechanically, UPS+TLFS fixation is superior to either UPS fixation or BPS fixation in improving stability and reducing stress. Bilateral pedicle screw fixation is intermediate, and UPS fixation is inferior.

A biomechanical comparison of 3 different posterior fixation techniques for 2-level lumbar spinal disorders

“…The addition of the TLFS to the UPS confers to it intermediate stability, superior to the UPS and inferior to the BPS in stability. However, this is different from what Gong et al 11 demonstrated in a finite element model, in which they revealed that UPSFS fixation was superior to either UPS or BPS fixation in improving stability and reducing stress biomechanically. The reason for this discrepancy might be explained by the variances of these two study methods.…”

Translaminar facet joint screw insertion with a rapid prototyping guide template: a cadaver study

“…Accordingly, several modified techniques have been assessed by finite element analysis and biomechanical tests, for example, unilateral pedicle screw (UPS), UPS with contralateral translaminar facet joint screw (UPS þ TFS) and etc. The results show that the stability of UPS þ TFS is similar to that of BPS for both 1-level and 2-level lumbar spinal disorders [5][6][7]. Moreover, some recent clinical studies also indicate TLIF using UPS þ TFS by paramedian mini-incision is a safe, feasible and effective method to treat one or two segment lumbar degenerative disorders [8,9].…”

Biomechanical study of unilateral pedicle screw combined with contralateral translaminar facet screw in transforaminal lumbar interbody fusion

“…A previous infinite element analysis showed that UPS + TLFS fixation is superior to either UPS or BPS in improving stability and reducing stress (Gong et al, 2014). However, all the mechanical parameters were set under normal conditions for infinite element model.…”

“…The finite element model could accurately simulate the movement of the lumbar spine in all directions to investigate the changes in internal stress accumulated on multiple areas of the lumbar spine and fixation devices during movement. In a previous study, an infinite element analysis showed that UPS + TLFS fixation is superior to either UPS or BPS in improving stability and reducing stress (Gong et al, 2014). However, all the mechanical parameters were set under normal conditions for the finite element model and some conditions seen in clinical settings were ignored when experimental parameters were set, such as vertebral body flexibility and effect of muscle tissues.…”

“…Many studies have been performed to compare the biomechanical ability between TLFS + UPS and BPS (Slucky et al, 2006;Sethi et al, 2011;Gong et al, 2014). Finite element based simulations were useful and efficient to evaluate the biomechanical ability of different fixation techniques (Freutel et al, 2014).…”