BACKGROUND:In 2019,the modified cortical bone trajectory technique was proposed by our team,significantly improving traditional methods.Previous studies have highlighted its superior biomechanical properties for segment fixation.However,a comprehensive systematic analysis of its specific biomechanical effects on adjacent segment degeneration is lacking,particularly regarding its influence on range of motion and intervertebral disc stress in posterior lumbar interbody fusion and transforaminal lumbar interbody fusion techniques.OBJECTIVE:To investigate the biomechanical effects of modified cortical bone trajectory screw techniques on adjacent segment degeneration in posterior lumbar interbody fusion and transforaminal lumbar interbody fusion.METHODS:CT scans were performed on three human cadaver specimens to establish and validate three-dimensional intact finite element models of the L1-S1 segment.For each of these,the posterior lumbar interbody fusion or transforaminal lumbar interbody fusion with three different fixation techniques was reconstructed at the L4-L5 segment.The L4-L5 segment was fixed using three different internal fixation techniques(modified cortical bone trajectory,cortical bone trajectory,and traditional pedicle screws).The range of motion and von Mises stress of the intervertebral disc of the L3-L4 and L5-S1 segments were recorded with a 400 N compressive load and 7.5 N moments in flexion,extension,left-right bending,and left-right rotation.The impacts of the three internal fixation techniques on adjacent segment degeneration in the two kinds of fusion were compared and analyzed.RESULTS AND CONCLUSION:(1)In the posterior lumbar interbody fusion model,the modified cortical bone trajectory screw group showed a reduced range of motion on adjacent segments(L3-L4,L5-S1)under six loading conditions compared to both the cortical bone trajectory screw group and traditional bone trajectory screw group.Specifically,the modified cortical bone trajectory screw group significantly reduced the maximum stress on the intervertebral disc in the superior adjacent segment(L3-L4)during extension compared to the traditional bone trajectory screw group(P=0.005),while the stress on the intervertebral disc in the inferior adjacent segment(L5-S1)exhibited greater dispersion.Similarly,the cortical bone trajectory screw group also significantly reduced the maximum stress on the intervertebral disc in the superior adjacent segment(L3-L4)during extension compared with the traditional bone trajectory screw group(P=0.03).(2)Compared with transforaminal lumbar interbody fusion,the three internal fixation techniques(modified cortical bone trajectory,cortical bone trajectory,and traditional pedicle screws)showed a trend of reduced range of motion in the inferior adjacent segment(L5-S1)under six loading conditions.In contrast,the maximum stress on the intervertebral discs in both the superior and inferior adjacent segments(L3-L4,L5-S1)exhibited an increasing trend in the posterior lumbar interbody fusion model.(3)It is concluded that in the posterior lumbar interbody fusion model,the modified cortical bone trajectory screw exhibited superior biomechanical properties in reducing the range of motion at adjacent segments,which may have a beneficial effect on reducing the risk of adjacent segment degeneration.

BACKGROUND:In 2019,the modified cortical bone trajectory technique was proposed by our team,significantly improving traditional methods.Previous studies have highlighted its superior biomechanical properties for segment fixation.However,a comprehensive systematic analysis of its specific biomechanical effects on adjacent segment degeneration is lacking,particularly regarding its influence on range of motion and intervertebral disc stress in posterior lumbar interbody fusion and transforaminal lumbar interbody fusion techniques.OBJECTIVE:To investigate the biomechanical effects of modified cortical bone trajectory screw techniques on adjacent segment degeneration in posterior lumbar interbody fusion and transforaminal lumbar interbody fusion.METHODS:CT scans were performed on three human cadaver specimens to establish and validate three-dimensional intact finite element models of the L1-S1 segment.For each of these,the posterior lumbar interbody fusion or transforaminal lumbar interbody fusion with three different fixation techniques was reconstructed at the L4-L5 segment.The L4-L5 segment was fixed using three different internal fixation techniques(modified cortical bone trajectory,cortical bone trajectory,and traditional pedicle screws).The range of motion and von Mises stress of the intervertebral disc of the L3-L4 and L5-S1 segments were recorded with a 400 N compressive load and 7.5 N moments in flexion,extension,left-right bending,and left-right rotation.The impacts of the three internal fixation techniques on adjacent segment degeneration in the two kinds of fusion were compared and analyzed.RESULTS AND CONCLUSION:(1)In the posterior lumbar interbody fusion model,the modified cortical bone trajectory screw group showed a reduced range of motion on adjacent segments(L3-L4,L5-S1)under six loading conditions compared to both the cortical bone trajectory screw group and traditional bone trajectory screw group.Specifically,the modified cortical bone trajectory screw group significantly reduced the maximum stress on the intervertebral disc in the superior adjacent segment(L3-L4)during extension compared to the traditional bone trajectory screw group(P=0.005),while the stress on the intervertebral disc in the inferior adjacent segment(L5-S1)exhibited greater dispersion.Similarly,the cortical bone trajectory screw group also significantly reduced the maximum stress on the intervertebral disc in the superior adjacent segment(L3-L4)during extension compared with the traditional bone trajectory screw group(P=0.03).(2)Compared with transforaminal lumbar interbody fusion,the three internal fixation techniques(modified cortical bone trajectory,cortical bone trajectory,and traditional pedicle screws)showed a trend of reduced range of motion in the inferior adjacent segment(L5-S1)under six loading conditions.In contrast,the maximum stress on the intervertebral discs in both the superior and inferior adjacent segments(L3-L4,L5-S1)exhibited an increasing trend in the posterior lumbar interbody fusion model.(3)It is concluded that in the posterior lumbar interbody fusion model,the modified cortical bone trajectory screw exhibited superior biomechanical properties in reducing the range of motion at adjacent segments,which may have a beneficial effect on reducing the risk of adjacent segment degeneration.

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.

BACKGROUND:Osteoporotic trabecular structures are insufficient to maintain screw holding force,often leading to spinal fixation failure.Currently,the following four aspects are mainly used to solve this problem:(1)screw material;(2)surface coating treatment;(3)screw channel solidification strategy;(4)screw shape.The screw channel of the modified cortical bone trajectory screw placement technique has been proven to have a good fixation effect,but there is an urgent need to develop matching screws.OBJECTIVE:To compare the biomechanical performance differences of various types of spinal cortical bone thread screws in the modified cortical bone trajectory fixation of lumbar vertebrae using the finite element method.METHODS:The L4 vertebral models were constructed based on the CT data of three adult wet lumbar specimens(two males and one female)and subjected to finite element analysis.In the modified cortical bone trajectory fixation technique,fully cortical bone thread screws(single thread screws)with lengths of 45 mm and diameters of 5.5 mm and 4.5 mm were used and considered as groups A and B,which were compared with those of the traditional pedicle screw technique group(group C,6.0 mm diameter,45 mm length,double-threaded screw)and the cortical bone trajectory screw group(group D,4.5 mm diameter,45 mm length,double-threaded screw).Axial pull-out force,screw stability(determined by the displacement ratio of upper,lower,left,and right loads),and anti-spin-out torque were measured to compare fixation strength of each group of screws.RESULTS AND CONCLUSION:(1)Axial pull-out force:Group A＞group B(P=0.003),and both group A and group B were greater than the group C(P＜0.001,P=0.003)and group D(all P＜0.001).(2)Screw stability:When load was applied in the upward and downward directions on the screw,the load displacement ratio of the four screw double threads was greater in group A than in group B(P＞0.05);both group A and group B were greater than the group C(all P＜0.001)and the group D(all P＜0.001).(3)Anti-spin-out torque:Group A＞group B(P=0.008),and both group A and group B were greater than the group C(P=0.008,P=0.131).(4)It is indicated that during modified cortical bone trajectory fixation of lumbar vertebrae,the novel spinal cortical bone thread screw demonstrates superior biomechanical performance compared to double thread screws applied in the clinically classic pedicle screw trajectory and cortical bone trajectory.Additionally,the novel spinal cortical bone thread screw(D=5.5 mm,L=45 mm)becomes the optimal adaptation for the modified cortical bone trajectory screw path.

BACKGROUND:Osteoporotic trabecular structures are insufficient to maintain screw holding force,often leading to spinal fixation failure.Currently,the following four aspects are mainly used to solve this problem:(1)screw material;(2)surface coating treatment;(3)screw channel solidification strategy;(4)screw shape.The screw channel of the modified cortical bone trajectory screw placement technique has been proven to have a good fixation effect,but there is an urgent need to develop matching screws.OBJECTIVE:To compare the biomechanical performance differences of various types of spinal cortical bone thread screws in the modified cortical bone trajectory fixation of lumbar vertebrae using the finite element method.METHODS:The L4 vertebral models were constructed based on the CT data of three adult wet lumbar specimens(two males and one female)and subjected to finite element analysis.In the modified cortical bone trajectory fixation technique,fully cortical bone thread screws(single thread screws)with lengths of 45 mm and diameters of 5.5 mm and 4.5 mm were used and considered as groups A and B,which were compared with those of the traditional pedicle screw technique group(group C,6.0 mm diameter,45 mm length,double-threaded screw)and the cortical bone trajectory screw group(group D,4.5 mm diameter,45 mm length,double-threaded screw).Axial pull-out force,screw stability(determined by the displacement ratio of upper,lower,left,and right loads),and anti-spin-out torque were measured to compare fixation strength of each group of screws.RESULTS AND CONCLUSION:(1)Axial pull-out force:Group A＞group B(P=0.003),and both group A and group B were greater than the group C(P＜0.001,P=0.003)and group D(all P＜0.001).(2)Screw stability:When load was applied in the upward and downward directions on the screw,the load displacement ratio of the four screw double threads was greater in group A than in group B(P＞0.05);both group A and group B were greater than the group C(all P＜0.001)and the group D(all P＜0.001).(3)Anti-spin-out torque:Group A＞group B(P=0.008),and both group A and group B were greater than the group C(P=0.008,P=0.131).(4)It is indicated that during modified cortical bone trajectory fixation of lumbar vertebrae,the novel spinal cortical bone thread screw demonstrates superior biomechanical performance compared to double thread screws applied in the clinically classic pedicle screw trajectory and cortical bone trajectory.Additionally,the novel spinal cortical bone thread screw(D=5.5 mm,L=45 mm)becomes the optimal adaptation for the modified cortical bone trajectory screw path.

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.