Finite element model analysis of lumbar biomechanical characteristics after nucleus discectomy

Abstract

Objective To use three-dimensional finite element model analysis for studying the lumbar biomechanical characteristics following nucleus discectomy in a patient with lumbar intervertebral disc protrusion.Methods A novel CAD method was adopted to accurately create the finite element models of L_4/5 segment,including the models for normal disc,degenerated disc,denucleated disc immediately after operation(denucleated model),and denucleated disc after a longer time period(scar growth model).Furthermore,the biomechanical parameters of the four models were examined under five different loads,namely,compression,flexion,extension,forward and backward shear loads.Results(1)Under the five loads,the stiffness of degenerated model was increased compared with that of the normal disc under all 5 different loads.(2)The stiffness of denucleated model was decreased than that of degenerated disc and increased than that of the normal disc.(3)The stiffness of scar growth model was enhanced and even surpassed that of the degenerated model due to the fact that the scar tissue filled the intradisc cavity.(4) The facet contact force was decreased under flexion,extension,and backward shear loads in denucleated model,and were increased under extension,forward and backward shear loads in scar growth model.(5) The backward bulge in the degenerated model was obviously slighter than that in the normal model.The backward bulge of denucleated model increased to some extent,and its inner annulus fibrous had inward bulging.Conclusion Nucleus discectomy has different effects on the biomechanics of lumbar motion segment in patients at different time points after operation.The impacts on lumbar stability and posterior structure are small immediately after nucleus discectomy,and the lumbar motion segment may stiffen and the stress of articular process may increase after a longer time period following nucleus discectomy.