Three-dimensional finite element analysis of oblique lateral lumbar interbody fusion combined with unilateral pedicle screw fixation

English Keywords:Finite element analysis  Lumbar fusion  Oblique lateral interbody fusion  Unilateral pedicle screw-rod fixation

English Abstract:

  【Abstract】 Objectives: To validate whether oblique lateral interbody fusion(OLIF) combined with unilateral pedicle screw-rod fixation can provide sufficient interbody stability for corresponding fusion and fixation segment through three-dimensional finite element analysis. Methods: To establish a three-dimensional finite element model of L3-S1 segments by Mimics, Geomagic, and 3-Matic software based on CT scan data of L3-S1 of healthy people, and it was set as normal control group(M0). On such basis, combined with Freeform and other software, OLIF stand alone model(M1) of L4/5, OLIF with unilateral pedicle screw-rod fixation (Wiltse approach) model(M2), and OLIF with bilateral pedicle screw-rod fixation(Wiltse approach) model(M3) were set up. 500N preload was applied on the upper surface of L3 and 10N·m moment was applied to simulate the physiological activities of lumbar spine in standing position, flexion, extension, lateral flexion and rotation. The above loading conditions were applied on both the M0, to validate the effectiveness of the model, and all finite element models, to observe the L4/5 segment range of motion(ROM), stress distribution of cage and pedicle screw-rod under different working conditions. The maximum stress of cage and pedicle screw-rod should be recorded. Results: It was validated that the finite element model was effective compared with the literature data. The ROM values of 4 groups in each movement state(flexion, extension, left and right lateral flexion, left and right rotation) were ranked from small to large: M3, M2, M1, and M0. M2 showed better stability in flexion and extension than M0 and M1. To be specific, the variation ranges under flexion and extension condition of M2 ROM were 75.43% and 85.20% respectively comparing to M0, and 58.88% and 70.39% respectively comparing to M1. M3 showed better stability in flexion and extension than M2, and the variation ranges of M3 ROM were 25.55% and 25.33% under flexion and extension respectively comparing to M2. Except smaller difference of variation range under right bending and right rotation conditions, the variation range of ROM of M2 comparing with M0 was much larger than that comparing with M3. Under all working conditions, the variation ranges of ROM of M2 when compared with M0 were 14.08%-85.20%, and that were 16.44%-25.55% when compared with M3. In terms of the peak stress of the cage, except that it was slightly higher in M2 than in M1 under condition of standing, in other motion states, it showed a decreasing trend with the increase of the number of additional pedicle screw-rod, which was most obvious in extension with a decreasing range of 109.14%. In terms of the peak stress of the screw-rod system, it was higher in M2 than in M3 under other states, except that peak stress value of M2 significantly lower than that of M3 in right lateral flexion and slightly lower than that of the M3 in left lateral bending. The differences of peak stress of screw-rod system between M2 and M3 were larger in right lateral bending and retroextension which were -33.09% and 76.79%. The peak stress of the screw-rod and cage in each of the three surgery groups was far from their yield strength respectively. Conclusions: The model of OLIF with unilateral pedicle screw-rod fixation can provide sufficient intervertebral stability for the corresponding fusion fixation segment.