| Objective:(1)Establish a finite element model of lumbar 4 bilateral spondylolysis for clinical research.(2)Establish two finite element models,which are one threaded pedicle screw dynamic fixation(TTL dynamic rod fixation system)and one threaded pedicle screw rigid fixation.(3)To explore the effects of different treatments on isthmus’ stability,vertebral stability,degeneration of adjacent intervertebral discs,internal fixation’s fracture.(4)Evaluate the effects of different treatments on lumbar spondylolysis.Materials and Methods:(1)Study subjects:We select 3 cases of inpatients in the Department of Orthopaedics,the First Affiliated Hospital of Chengdu Medical College,and their diagnoses are lumbar 4 bilateral spondylolysis,from 20 to 59 years old.Simultaneously,lumbar spine oblique films,lumbar CT and lumbar MRI prove lumbar 4 bilateral spondylolysis without obvious degeneration of adjacent intervertebral discs and hyperplasia of facet joint.Furthermore,bone mineral density examination shows normal bone mass.We must exclude patients with spinal fracture or other spinal disorders.(2)Data collection: Three volunteers need receive lumbar vertebrae scanning and image processing by Siemens 64-row CT.Thickness of the scan is 0.625 mm and its range is from L1 to S1 spine,including positions of coronal,sagittal,transverse.Select relevant data to import the U disk in DICOM format as backups,and apply Mimics(image interactive system)to process the data.(3)Establish a finite element model of lumbar 4 bilateral spondylolysis: The CT data are imported into Mimics,and we can distinguish CT data of different organizational structures in order to select bones’ threshold segmentation.Then,the preliminary model is established by processing the data.(4)Amend the finite element model of lumbar 4 bilateral spondylolysis: Finite element model was modified and perfected by Geomagic modification system.Mimics was introduced to generate different lumbar structures(cortical bone,cancellous bone,nucleus pulposus,fibrous ring,etc.)(5)Establish dynamic fixation(TTL dynamic rod fixation system)and rigid fixation by Solider Works.(6)Use Abaqus/Hyper Mesh to assemble the internal fixation system in the spondylolysis model.Finally establish three models of lumbar 4 bilateral spondylolysis,which are unfixed model,dynamic fixation and rigid fixation,and the materials of different lumbar structures and internal fixation were assigned.(7)Various loads,which are vertical,forward flexion,posterior extension,lateral flexion and rotation,are applied to the three groups by Abaqus software.Then we analyze the displacement of vertebral body and isthmus,the stress of lumbar 3/4 intervertebral disc,internal fixation’s stress.Then we collect data for charting and analysis by SPSS software.Result:1.By the cloud maps of lumbar 3 / 4 intervertebral disc’s stress and the comparison of intervertebral disc’s stress in three different treatments under same motion state,we get some results about the three models: under motion state of vertical,rigid fixation>dynamic fixation>unfixed method(these two kinds of fixations have no statistical significance,P>0.05;but the fixations and unfixed method are statistically different,P<0.05).Under motion state of forward flexion,posterior extension,lateral flexion and rotation,we find:rigid fixation>dynamic fixation>unfixed method(these three kinds of models are statistically different,P<0.05).2.By the cloud maps’ analysis of lumbar 4 bilateral spondylolysis’ displacement and the comparison of isthmus’ stress in three different treatments under same motion state,we find some difference,which is under motion state of vertical,lateral flexion and rotation: unfixed method>dynamic fixation>rigid fixation(these two kinds of fixations have no statistical significance,P>0.05;but the fixations and unfixed method are statistically different,P<0.05).Under motion state of forward flexion and posterior extension,we find some difference:unfixed method>dynamic fixation>rigid fixation(these three treatments are are statistically different,P<0.05).3.By the cloud maps’ analysis of the overall displacement of the lumbar vertebrae and the comparison of the overall displacement in three different treatments under same motion state,we get some results about the three models:under motion state of vertical,lateral flexion and rotation,unfixed method>dynamic fixation>rigid fixation(these two kinds of fixations have no statistical significance,P>0.05;but the fixations and unfixed method are statistically different,P<0.05).Under motion state of forward flexion and posterior extension,we find: unfixed method>dynamic fixation>rigid fixation(these three kinds of models are statistically different,P<0.05).4.By analysis stress of internal fixation of two kinds of operation methods showed that the stress of internal fixation of two kinds of operation methods in same lumbar motion state was compared,vertical,lateral flexion,rotation state,rigid fixation >dynamic fixation,the two had statistical significance(P < 0.05);in extension state,dynamic fixation > rigid fixation,the two had statistical significance(P < 0.05);in flexion state,the two kinds of operation methods had no significant difference(P <0.05).Statistical significance(P > 0.05).Conclusion:This experiment utilizes three-dimensional finite element to simulate three different treatments,which include unfixed method,dynamic fixation(TTL elastic rod),and rigid fixation about lumbar 4 bilateral spondylolysis.Meanwhile,relevant indexes about the three groups’ models under different motion state,which include overall stability,isthmus’ s stability,degeneration of adjacent intervertebral discs,the risk of internal fixation’s fracture,must be taken into consideration in order to analyze the biomechanics’ differences between the three different treatments.The motion state include vertical,forward flexion,posterior extension,lateral flexion and rotation.We define these two internal fixation methods as surgical fixation and unfixed method as conservative treatment.1.Dynamic fixation has less stress on the adjacent intervertebral discs and delays adjacent intervertebral discs’ degeneration better than rigid fixation.To a certain degree,dynamic fixation can reduce the risk of adjacent vertebral body’s disease.Surgical fixation increases stress of adjacent intervertebral discs.2.These two internal fixation methods can get similar isthmus’ stability,and benefit fusion of isthmus’ bone graft.Surgical fixation can gain better isthmus stability than conservative treatment.3.These two internal fixation methods can get similar overall stability of lumbar.These advantages can benefit recovery of normal biomechanical conduction’s vertebral Body and reduce complications caused by lumbar instability.Surgical fixation can provide lumbar better overall stability than conservative treatment.4.The peak of dynamic fixation’s average stress is less than rigid fixation,and at the same time,the risk of internal fixation’s fracture is lower.5.In summary,By comparing with the two internal fixation methods,we conclude that dynamic fixation can delay adjacent intervertebral discs’ degeneration and reduce the risk of internal fixation’s fracture.these two internal fixation methods can get some similar results,including the stability of the spine,isthmus’ s stability.the surgical fixation is better than conservative treatment in recovering the stability of the spine and improving isthmus’ s stability.Therefore,it is feasible to use dynamic fixation to treat spondylolysis,not only to retain segment activity and reduce the incidence of adjacent spondylosis and reduce the risk of internal fixation’s fracture,but also to provide the stability required for bone graft fusion. |
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