The Finite Element Analysis Of Three Different Posterior Fixation Techniques In Lumbar Spine For Two Levels

The aim of the study was to compare the biomechanics of the following three fixation techniques:bilateral pedicle screws fixation (BPS), unilateral pedicle screws fixation (UPS), and unilateral pedicle screws supplemented with translaminar facet screws (UPS+TLFS).The experiment was carried out in using a intact L3-L5FE (finite element) model. After the model was tested to be validated, three FE models were reconstructed by different fixation techniques following the validated intact model removed the left L3L4and L4L5facet joints. A compressive preload of500N combined with8N·m moment in flexion, extension, lateral bending, and axial rotation was loaded to the models. The angular displacement and the stress distribution were recorded. The results showed that the UPS fixation had the most variation in angular displacement compared with the BPS fixation and the UPS+TLFS fixation, the BPS fixation fell in between, while the UPS+TLFS fixation got few mobility and represented to be the most stable fixation technique. Considering the stress distribution, most of the stress concentrated on the body and tail part of the pedicle screws and rods in the UPS and BPS fixations, but the stress in UPS+TLFS fixation was gathered on the rods and TLFS pierced the facet joint part. The middle pedicle screw was almost endured no stress compared with the upper and the lower one. The maximum stress on the fixation devices was much higher in the FE models of UPS technique compared with the models of BPS and UPS+TLFS techniques, also the BPS fixation fell in between, while the maximum stress in the UPS+TLFS fixation is the lowest. In conclusion, no matter the angular displacement or the maximum stress, the UPS technique stood the higher level than the others, the BPS technique fell in between, and the UPS+TLFS technique was the minimum in the three models.