The effect of different types of laminectomy on biomechanical characteristics of BioFlex system

English Keywords:Finite element analysis  BioFlex system  Laminectomy  Range of motion  Facet contact force

English Abstract:

  【Abstract】 Objectives: To investigate the effect of different type of laminectomy on the biomechanical characteristics of BioFlex system by using finite element method. Methods: The normal L3-L5 geometry model was established by three-dimensional reconstruction software Mimics 10.01 and the BioFlex system geometry model was established by reverse engineering software ProE, and were assembled according to surgery and imported into ANSYS Workbench 14.0 finite element analysis software to establish four different types of laminectomy in finite element models, which included Intact(INT), L4-L5 laminectomy + 1/2 facet joint removal + Bioflex(MF-BF), L4-L5 laminectomy + total facet joint removal + Bioflex(TF-BF), L4-L5 laminectomy + discectomy + Bioflex(D-BF). All models were loaded under 1200N to simulate different spinal motions(flexion, extension, lateral bending and rotation) with torque 8, 8, 6, and 4Nm, respectively. The range of motion(ROM) at fixed and adjacent segment, the annulus stress and facet contact force(FCF) at adjacent segment were measured and analyzed. Results: The ROM at fixed segment decreased dramatically after laminectomy and placing of BioFlex system compared with INT group(P＜0.05), and the ROM of TF-BF group decreased up to 77.2% in flexion and the ROM of MF-BF group decreased up to 37.4%, 67.2%, 83.1% in extension, lateral bend, and rotation respectively; while the ROM at adjacent segment increased obviously compared with INT group(P＜0.05), the ROM of MF-BF group increased up to 22.9% in flexion, and the ROM of TF-BF group increased up to 18.2%, 32.1% in extension, lateral bend respectively and the ROM of DF-BF group increased up to 13.8% in rotation. The change of ROM at fixed and adjacent segment were little under different type of laminectomy, there was no significant differences between groups of MF-BF, TF-BF and DF-BF(P＞0.05). The annulus stress and FCF at adjacent segment dramatically increased after laminectomy and placing of BioFlex system, which had significant difference compared with INT group(P＜0.05). The FCF of TF-BF group increased up to 81.6%, 77.3% in extension, rotation respectively, and the FCF of DF-BF group increased up to 60.5% in lateral bend. The annulus stress of DF-BF group increased up to 46.6% in flexion and the annulus stress of MF-BF group increased up to 11.8%, 63.5%, 51.3% in extension, lateral bend and rotation. The change of FCF and annulus stress at adjacent segment was little under different type of laminectomy, there was no significant differences between groups of MF-BF, TF-BF and DF-BF(P＞0.05). Conclusions: The ROM at fixed segment significantly decreases after placing of Bioflex system, while the ROM at adjacent segment increases obviously. The different type of laminectomy has insignificant influence on the ROM at fixed segment and adjacent segment after placing of Bioflex system. The annulus stress and FCF at adjacent segment significantly increases after placing of Bioflex system, there is no significant influence on the annulus stress and FCF at adjacent segment with different type of laminectomy.