3D Digital Measurement And Finite Element Analysis Of Bony Articular Surface Of Facet Joint Lumbar Disc Herniation In Adolescents 13～18 Years Old

Objectives 1.To observe the bone structure of facet joints in normal and adolescent lumbar disc herniation（ALDH）from 13 to 18 years old,and to provide anatomical reference for early diagnosis and treatment of LDH.2.Observe different facet tropism（FT）standards,establish lumbar biomechanical finite element models of ALDH and normal people,summarize the characteristics of biomechanical changes,and provide reference for etiological analysis.Materials and methods:1.Computed Tomography（CT）imaging data of 32 patients who diagnosed by two or more deputy chief radiologists of imaging department and spinal surgery,excluding other spinal deformities and other diseases with lumbar disc herniation aged 13～18 years old in Inner Mongolia were retrospectively collected.CT imaging data of 62 patients who received health examination at the same period（no spinal diseases in the same age group）were selected as the control group the data were imported into mimics 21.0,including facet height,facet joint width,articular process thickness,interarticular facet spacing,facet joint thickness,facet joint cross-sectional area,facet joint angle,sagittal angle and transverse interfacet angle.ALDH group and control group were measured left and right observation indexes,and paired t test was used for left and right comparison;control group was divided into two groups according to"3-year-old group",which were recorded as 13-15-year-old group and 16-18-year-old group,and independent sample t test was used for observation indexes between different genders;ALDH group and control group were compared by independent sample t test.2.Combined with Mimics 21.0,3-Matic Medical 13.0,Geomagic wrap,Hyper Mesh and finite element software ABAQUS to establish three-dimensional finite element models of normal and adolescent lumbar disc herniation,according to different standards of facet joint asymmetry,including symmetric model FT0°model,asymmetric model FT5°model,asymmetric model FT 5°model Methods:the data of 3 normal adolescents aged 13～18 years old and 3 adolescent patients with L_4-5 lumbar disc herniation were collected.They were all male,with an average age of（16.67±2.07）years old.They were divided into control group and ALDH group.The stress of intervertebral disc under different torque loads（upright position,lateral flexion and rotation）was analyzed and compared.Results 1.（1）Facet joint height:In the control group,there was significant difference between male and female in L₅S₁segment of 13-15-year-old group（P<0.05）,male（15.57±1.71）mm was less than female（16.81±2.62）mm;there was significant difference between L_4-5 segment and L₅S₁segment（P<0.05）,and the largest value of L₅S₁ was（16.27±2.27）mm.（2）Facet joints width:There were significant differences between L_3-4,L_4-5 and L₅S₁（P<0.05）,which increased with the increase of vertebral sequence.（3）Articular process thickness:The thickness of superior articular process decreased with the increase of vertebral sequence.The thickness of inferior articular process decreased with the increase of vertebral sequence.（4）Interarticular facet spacing:there were significant differences in the height of facets and facets from L₃to L₅（P<0.05）,and it showed a decreasing trend with the increase of facets.（5）Facet joint thickness:male（1.63±0.32）mm and female（1.38±0.25）mm（P<0.05）,the difference was statistically significant.There were significant differences in the thickness of facet joint between L₃-L₅ sequences（P<0.05）.L₃-L₅increased first and then decreased with the sequence,L_4-5was the largest（1.6±0.31）mm,L₅S₁was the smallest（1.37±0.38）mm.（6）Facet joint cross-sectional area:There was a significant difference between male and female in 16-18 years old group（P<0.05）.Male（22.1±3.04）mm was larger than female（18.92±3.71）mm².There were significant differences between L_3-4 and L_4-5,L₅S₁ segments（P<0.05）.The minimum value of L_3-4 segment was（21.61±4.01）mm².（7）Facet joint Angle:In the control group,L₃-L₅ from top to bottom were（39.67±8.49）°,（48.55±8.89）°,（51.64±8.83）°;in ALDH group,L₃-L₅ from top to bottom were（44.09±8.48）°,（50.25±7.63）°,（54.2±10.14）°;L₃-L₅ showed an increasing trend with the change of vertebral sequence.The level of L_3-4 and L₅S₁ in control group was lower than that in ALDH group（P<0.05）.（8）Sagittal Angle and Transverse interfacet angle:There was no significant difference between L_3-4 and L_4-5segments（P>0.05）,but the L₅S₁ segment was the largest,which was（171.84±4.76）°and（81.84±4.76）°respectively.（9）The control group compared with ALDH group,L_3-4 facet joint angle（P<0.05）,the difference was statistically significant,L_4-5 facet joint height,inferior articular process,facet joint thickness（P<0.05）,the difference was statistically significant,L₅S₁ inferior articular process,facet joint thickness,facet joint angle（P<0.05）,the difference was statistically significant.（10）According to Chi square test,there was significant difference between ALDH group and control group at FT10 degree（P<0.05）.2.（1）The three-dimensional finite element model of L₃-L₅segment of 6 normal male and adolescent patients with lumbar disc herniation was established,and the stress and displacement cloud maps of neutral position,flexion,extension,lateral flexion and rotation and adolescent lumbar disc herniation were obtained.（2）The stress on the posterior side of L_4-5 fibrous annulus increased when the articular process joint angle of normal adolescents was symmetrical in the neutral position.（3）Under different working conditions,the stress annulus of intervertebral disc was larger than that of nucleus pulposus,and the stress of annulus fibrosus was flexion>neutral position>extension.4.In ALDH group,the stress on the left side of facet joint was greater than that on the right side in FT10°model,and the stress on the posterior side of annulus fibrosus of L_4-5 segment increased significantly.Under lateral flexion condition,the stress on the left side of the left flexor ring was significantly higher than that on the right side of the right flexor ring（P<0.05）.Under the rotating condition,the stress on the left and right sides of the fiber ring is greater than that on the back side.Conclusion:1.When ALDH occurred in L₅S₁ segment,there were significant differences in facet joint angle between the two groups,but there was no significant difference in the control group;in the control group,there were differences in facet joint thickness and facet joint cross-sectional area between male and female in L₃-L₅ segment,and the male was generally larger than the female.2.The greater facet joint height,inferior articular process is larger and the smaller the thickness of facet joint can indicate that lumbar disc herniation is prone to occur.Facet joint asymmetry can be considered as a risk factor for ALDH.4.Compared with ALDH group,the stress of intervertebral disc increased under different postures,which may increase the shear load of intervertebral disc and aggravate the process of intervertebral disc degeneration.Compared with adolescent patients with lumbar disc herniation,the stress of intervertebral disc in the control group increased under different postures,which may increase the shear load of intervertebral disc and aggravate the process of intervertebral disc degeneration.5.When the degree of left-right asymmetry of facet joint is more than 10 degrees,the stress on the side with small degree is greater.Facet joint asymmetry can lead to the overload of vertebral body and intervertebral disc,leading to spinal instability.6.The stress of intervertebral disc in extension is less than that in neutral position and flexion.Extension can relieve the pressure of intervertebral disc and play an auxiliary role in the recovery of adolescent patients with lumbar disc herniation.