Biomechanical Study Of Minimally Invasive Transforaminal Lumbar Interbody Fusion Using Different Internal Fixation Systems

Objective:(1) To establish the models of minimally invasive transforaminallumbar interbody fusion (MIS-TLIF) at L4~L5using three kinds of internal fixationsystems with fresh-frozen human cadaveric lumbar spines;(2) To compare thebiomechanics of the three kinds of internal fixation systems, and provide theoreticalbasis for clinical choice of internal fixation system.Methods: Six fresh human lumbar spines (L1~S1) were using to establish thefollowing four models at L4~L5:(1) intact model (INT);(2) unilateral pedical screwfixation model (UPS);(3) bilateral pedical screw fixation model (BPS);(4) unilateralpedicle screws and a translaminar facet screw (TLFS) fixation model (UPS+TLFS).After validated to be effective, the models were tested by applying pure moments of8Nm. The operation segment L4~L5and adjacent segment L3~L4range of motion(ROM) and stiffness for each construct were obtained by applying pure moments inflexion, extension, lateral bending, and axial rotation. The biomechanics of the fourmodels were compared.Results:(1) The INT, UPS, BPS, and UPS+TLFS models were established andvalidated to be effective;(2) Compared with the INT model, the three fixation models,including BPS, UPS, and UPS+TLFS models, decreased the ROM and increased thestiffness of the fixation segment L4~L5in all direction of motion. The stiffest modelwas BPS model, and the lowest was UPS model;(3) The UPS model was significantlydifferent than BPS and UPS+TLFS model in the right lateral bending and rotating inL4~L5ROM (P<0.05);(4) The BPS model was stiffer than INT and UPS model inall loading modes (P<0.05), and UPS+TLFS model except in the right lateral bending(P<0.05);(5) Compared with the INT model, the three fixation models increased theROM of the adjacent segment L3~L4in all direction of motion (P<0.05). The mostwas BPS model, and the lowest was UPS model;(6) The most growth was in BPSmodel, which was significantly different than INT model in all loading modes (P<0.05),and UPS+TLFS model in extension, lateral bending, and left axial rotation (P<0.05).Conclusion:(1) The INT, UPS, BPS, and UPS+TLFS models were establishedand validated to be effective;(2) The BPS fixation had the biggest strength and the most increasing of the ROM of the adjacent segment;(3) The UPS fixation was the leaststable, especially in lateral bending and axial rotation;(4) The hybrid construct ofUPS+TLFS fixation was considered appropriate internal fixation for MIS-TLIF for thereasons that it might likely achieve the biomechanical property of BPS fixation but lessinfluence to the ROM of the adjacent segment.