Objective To make a comparative analysis on mechancial properties of the modified cortical bone trajectory(MCBT)nailing technique using a novel variable-diameter screw and the traditional pedicle nailing technique using the cement-augmented pedicle screw(CAPS)in the L4 vertebral body.Merthods CAPS and MCBT instrumentation in the L4 vertebral body model were established by obtaining CT scan data from osteoporotic patients.The finite element method was used to compare the stability,screw axial pull-out force and lumbar spine motion under four working conditions(upper,lower,left and right loads)by using different nailing techniques.Results The axial pull-out force of the screws in MCBT group was 25.3％higher than that of the CAPS group(P＜0.05);the load-displacement ratios of the screws in MCBT group were 14.9％(P＞0.05),23.2％(P＞0.05),and 19.1％(P＜0.05)higher than those of CAPS group under the lower,left,and right working conditions,respectively;the load-displacement ratios of the screws in MCBT group were slightly lower than those of CAPS group under the upper working condition,but the differences were not statistically significant(P＞0.05);under the anterior and posterior flexion conditions,the lumbar spine motion of MCBT group was reduced by 13.3％and 2.5％,respectively,compared with CAPS group;under the left lateral bending,right lateral bending,and axial rotational conditions,the lumbar spine motion of MCBT group was improved by 69.1％,74.6％,and 118.1％,respectively,compared with CAPS group,but these differences were not statistically significant(P＞0.05).Conclusions MCBT screw was slightly better than CAPS in axial resistance to extraction force,and stability of vertebral anterior flexion under lower,left and right working conditions,and slightly weaker than CAPS in stability under upper,left lateral bending,right lateral bending,and axial rotational conditions.This study demonstrates that MCBT screw has certain advantages over CAPS,providing a pre-basic foundation for the clinical application of MCBT nailing technique for treating osteoporosis.

Objectives:To evaluate the difference in biomechanical properties of lumbar spine between tradi-tional trajectory(TT)and modified cortical bone trajectory(MCBT)pedicle screws in different osteoporotic condi-tions using finite element analysis.Methods:CT scanning was used to obtain lumbar spinal tomographic im-ages of osteoporotic patients,and then the L4 lumbar spine structure was reconstructed in three dimensions and validated.Two nail channels were constructed by varying the bone density as osteopenia(A1),moderate osteoporosis(A2),and severe osteoporosis(A3),respectively.One was a conventional double-threaded pedicle screw used in TT with a diameter of 6mm and an overall length of 45mm(TT group),the other was a vari-able-diameter,all-cortical bone threaded pedicle screw used in MCBT with a diameter of 4-5.5mm and an overall length of 45mm(MCBT group).The effects of the two designs on screw pullout resistance,stability(load-displacement ratio of upward,downward,left and right working conditions,defined as the ratio of load value to displacement when screw tail end displaced 0.1mm upward,downward,left and right towards its vertical axis)and lumbar spine mobility(when forward flexion,backward extension,lateral bending and axial rotation)were analyzed under different osteoporotic conditions.Results:In terms of axial pullout force,the MCBT group significantly improved 93.5％,96.5％,and 98.5％than the TT group in A1,A2,and A3,respec-tively.In terms of stability,at upward,downward,left,and right working conditions,the load-displacement ratios of the screws in the MCBT group were improved in comparison with the TT group in A1,A2,and A3,respectively,by 42.2％,40.8％,41.7％;49％,49％,51.5％;82.4％,81.5％,85.2％;73.1％,70.8％,72.5％.In terms of lumbar spine mobility,at forward flexion,under A1,A2,and A3,the TT group increased by 25％,26.6％and 28.7％compared to the MCBT group,respectively;at backward extension,the TT group increased by 24.5％and 22.9％compared to the MCBT group under A1 and A2,respectively,whereas under A3,the difference was not significant(P＞0.05);at lateral bending and axial rotation,the MCBT group had a slightly slight increase compared to the TT group under A1,A2,and A3(P＞0.05).Conclusions:Under different degrees of osteoporosis grading,MCBT technique was inferior in stability to TT technique only in spinal axial rotation and lateral flexion,while it outperformed TT technique in axial pull-out force,screw stability,and spinal stability during forward flexion and backward extension.

Objectives:To evaluate the difference in biomechanical properties of lumbar spine between tradi-tional trajectory(TT)and modified cortical bone trajectory(MCBT)pedicle screws in different osteoporotic condi-tions using finite element analysis.Methods:CT scanning was used to obtain lumbar spinal tomographic im-ages of osteoporotic patients,and then the L4 lumbar spine structure was reconstructed in three dimensions and validated.Two nail channels were constructed by varying the bone density as osteopenia(A1),moderate osteoporosis(A2),and severe osteoporosis(A3),respectively.One was a conventional double-threaded pedicle screw used in TT with a diameter of 6mm and an overall length of 45mm(TT group),the other was a vari-able-diameter,all-cortical bone threaded pedicle screw used in MCBT with a diameter of 4-5.5mm and an overall length of 45mm(MCBT group).The effects of the two designs on screw pullout resistance,stability(load-displacement ratio of upward,downward,left and right working conditions,defined as the ratio of load value to displacement when screw tail end displaced 0.1mm upward,downward,left and right towards its vertical axis)and lumbar spine mobility(when forward flexion,backward extension,lateral bending and axial rotation)were analyzed under different osteoporotic conditions.Results:In terms of axial pullout force,the MCBT group significantly improved 93.5％,96.5％,and 98.5％than the TT group in A1,A2,and A3,respec-tively.In terms of stability,at upward,downward,left,and right working conditions,the load-displacement ratios of the screws in the MCBT group were improved in comparison with the TT group in A1,A2,and A3,respectively,by 42.2％,40.8％,41.7％;49％,49％,51.5％;82.4％,81.5％,85.2％;73.1％,70.8％,72.5％.In terms of lumbar spine mobility,at forward flexion,under A1,A2,and A3,the TT group increased by 25％,26.6％and 28.7％compared to the MCBT group,respectively;at backward extension,the TT group increased by 24.5％and 22.9％compared to the MCBT group under A1 and A2,respectively,whereas under A3,the difference was not significant(P＞0.05);at lateral bending and axial rotation,the MCBT group had a slightly slight increase compared to the TT group under A1,A2,and A3(P＞0.05).Conclusions:Under different degrees of osteoporosis grading,MCBT technique was inferior in stability to TT technique only in spinal axial rotation and lateral flexion,while it outperformed TT technique in axial pull-out force,screw stability,and spinal stability during forward flexion and backward extension.

Objective To make a comparative analysis on mechancial properties of the modified cortical bone trajectory(MCBT)nailing technique using a novel variable-diameter screw and the traditional pedicle nailing technique using the cement-augmented pedicle screw(CAPS)in the L4 vertebral body.Merthods CAPS and MCBT instrumentation in the L4 vertebral body model were established by obtaining CT scan data from osteoporotic patients.The finite element method was used to compare the stability,screw axial pull-out force and lumbar spine motion under four working conditions(upper,lower,left and right loads)by using different nailing techniques.Results The axial pull-out force of the screws in MCBT group was 25.3％higher than that of the CAPS group(P＜0.05);the load-displacement ratios of the screws in MCBT group were 14.9％(P＞0.05),23.2％(P＞0.05),and 19.1％(P＜0.05)higher than those of CAPS group under the lower,left,and right working conditions,respectively;the load-displacement ratios of the screws in MCBT group were slightly lower than those of CAPS group under the upper working condition,but the differences were not statistically significant(P＞0.05);under the anterior and posterior flexion conditions,the lumbar spine motion of MCBT group was reduced by 13.3％and 2.5％,respectively,compared with CAPS group;under the left lateral bending,right lateral bending,and axial rotational conditions,the lumbar spine motion of MCBT group was improved by 69.1％,74.6％,and 118.1％,respectively,compared with CAPS group,but these differences were not statistically significant(P＞0.05).Conclusions MCBT screw was slightly better than CAPS in axial resistance to extraction force,and stability of vertebral anterior flexion under lower,left and right working conditions,and slightly weaker than CAPS in stability under upper,left lateral bending,right lateral bending,and axial rotational conditions.This study demonstrates that MCBT screw has certain advantages over CAPS,providing a pre-basic foundation for the clinical application of MCBT nailing technique for treating osteoporosis.

Objective To explore the mechanical properties of modified cortical bone trajectory(MCBT)and cortical bone trajectory(CBT)in lumbar revision surgery using finite element analysis and to analyze the advantages of MCBT over CBT in lumbar revision.Methods A three-dimensional(3D)model of the L1-5 vertebral body,endplate,annulus fibrosus,and nucleus pulposus was established based on CT tomography data.The traditional trajectory(TT)was used for pedicle screw placement in the vertebral body model;then,the TT screws were removed,retaining the TT screw path,and revision screws were placed on the vertebral body with MCBT and CBT screws.The mechanical properties of the MCBT and CBT during revision surgery were analyzed using finite element analysis.Results Under flexion,extension,lateral bending,and axial rotation,the range of motion(ROM)in the CBT revision group decreased by 12.07％,19.60％,8.72％,and 7.66％,respectively;the annulus stress of L3-4 segment increased by 11.27％,30.43％,35.52％,and 25.36％,respectively;and the annulus stress of L4-5 segment decreased by 39.84％,52.64％,23.91％,and 15.77％,respectively,compared with the control group.The ROM in the MCBT revision group decreased by 13.18％,20.27％,25.63％,and 8.59％,respectively;the annulus stress of the L3-4 segment increased by 10.41％,21.60％,15.83％,and 18.41％,respectively;and the annulus stress of the L4-5 segment decreased by 37.14％,61.94％,39.46％,and 35.23％,respectively,compared with the control group.The ROM of the MCBT revision group decreased by 1.26％,0.83％,18.53％,and 1.00％,respectively.The annulus stress of the L3-4 segment decreased by 0.77％,6.77％,14.53％,and 5.54％,respectively,whereas that of the L4-5 segment decreased by 2.82％,15.91％,19.79％,and 8.75％,respectively,compared to the CBT revision group.Compared with the CBT revision group,the annulus stress of the L4-5 segment in the MCBT revision group increased by 4.49％under flexion and decreased by 19.65％,20.44％,and 23.11％under extension,lateral bending,and axial rotation,respectively.Conclusions Both MCBT and CBT can provide mechanical properties that meet the requirements of vertebral fixation,and the fixation performance and safety of MCBT are comparable to those of CBT.This study provides a reference for using the MCBT and CBT techniques in revision surgery in clinical practice.

Objective To study mechanical properties of traditional trajectory (TT) and modified cortical bone trajectory (MCBT) on osteoporotic vertebrae through finite element analysis. Methods The three-dimensional model of L4 segment was established, and pedicle screw (PS) (diameter 6.0 mm, length 45 mm) and MCBT screw (diameter 4.5 mm, length 40 mm) were placed on both sides of the lumbar spine. The pull-out strength and the load-displacement ratio of screws in two different screw trajectories under up, down, left, right working conditions were analyzed, and the stability between the screw and vertebral body under osteoporotic conditions was evaluated. Results Compared with TT, the pull-out strength of MCBT screw was increased by 13.1%. Compared with PS, the load-displacement ratio of MCBT screw under up, down and left working conditions was increased by 57.2%, 32.4%, and 31.6%. Under right working condition, although the load-displacement ratio of MCBT screw was higher than that of PS, no statistical difference was found. The load-displacement ratio of vertebral body in MCBT group under lateral bending and axial rotation was significantly higher than that in TT group. The load-displacement ratio of vertebral body in MCBT group under flexion was lower than that in TT group. Although the load-displacement ratio of vertebral body in MCBT group under extension was higher that that in TT group, no statistical difference was found. Conclusions MCBT is superior to TT in pull-out strength, screw stability and vertebral body stability under lateral bending and axial rotation, but its vertebral body stability under flexion and extension was weaker than that of TT. The research findings demonstrate the superiority of MCBT under osteoporotic conditions and lay the foundation for clinical application of MCBT.