| Objective: The pedicle screw fixation technique has been the mainstay in lumbar spine surgery for decades,but cancellous bone degenerates with aging,which may cause postoperative pedicle screw fixation failure.The cortical bone trajectory(CBT)technique was proposed for compensating certain defects of the pedicle screw fixation technique in2009.However,the CBT technique failed to make full use of the bone cortex along the screw tract unreservedly.To compensate for the defects of the CBT technique in anatomical reference,entry point,and screw trajectory,the modified cortical bone trajectory(MCBT)technique was previously proposed by our team,which reached the medial wall of the pedicle and the lateral margin of the superior endplate of the vertebral body.To address the need for both minimal invasiveness and thorough decompression,the current study was aiming to investigate the biomechanical properties of the hybrid fixation technique with bilateral modified cortical bone trajectory screw(BMCS)and bilateral pedicle screw(BPS)in L4-L5 transforaminal lumbar interbody fusion(TLIF)model.Methods: CT scan was performed using three human wet cadaveric lumbar specimens.Three finite element(FE)models of the L1-S1 lumbar spine including five lumbar vertebrae and sacrum,five intervertebral discs with the upper and lower vertebral endplates,seven ligaments,and facet joint cartilages were established.The FE models were validated and the TLIF surgery was simulated.The BPS-BMCS(BPS at L4 and BMCS at L5),BMCS-BPS(BMCS at L4 and BPS at L5),BPS-BPS(BPS at L4 and L5),and BMCS-BMCS(BMCS at L4 and L5)fixation techniques were performed at the L4-L5 segment of each FE model.A reference point was created at the upper center of the L1 vertebral endplate,and 400 N compressive load with 7.5 Nm moment was applied to the reference point for stimulating flexion,extension,lateral bending,and rotation.The range of motion(ROM)of the L4-L5 segment,von Mises stress of the intervertebral cage,screw,and rod were recorded and discussed.Results: The BPS-BMCS group showed a lower ROM in extension(0.52±0.09°)and rotation(0.54±0.07°),and the BMCS-BMCS group showed a lower ROM in flexion(0.53±0.16°)and lateral bending(0.49±0.36°).The BPSBPS group showed lower von Mises stress in flexion(51.21±23.64 MPa)and lateral bending(65.40±0.76 MPa).The BMCS-BPS group showed lower von Mises stress of the cage and rod in extension(58.88±10.45,59.72±9.46 MPa)and rotation(48.37±17.71,47.92±2.28 MPa),but the BMCS-BMCS group showed greater von Mises stress of the cage almost in flexion(54.76±29.24 MPa),lateral bending(72.66±2.40 MPa),rotation(53.79±20.22 MPa).The BMCS-BPS group showed the lower von Mises stress of the screw in flexion(66.42±35.07 MPa),extension(171.86±23.22 MPa),lateral bending(200.34±91.11 MPa),and rotation(193.35±68.09 MPa).The BMCS-BMCS group showed almost higher von Mises stress of the rod in flexion(45.50±22.12 MPa),extension(119.17±83.94 MPa),lateral bending(119.35±43.20 MPa),and rotation(113.32±103.50MPa).Conclusion: The hybrid BPS-BMCS technique offered superior stability in extension and rotation and a lower risk of screw and rod breakage than the BPS-BPS,BMCS-BMCS,and BMCS-BPS techniques in four motions.The BMCS-BMCS technique offered superior stability in flexion and lateral bending.The hybrid BMCS-BPS technique offered a lower risk of cage subsidence and rod breakage.Compared with the traditional trajectory technique and cortical bone trajectory technique,the hybrid BPS-BMCS,and BMCS-BPS techniques might be an alternative in TLIF surgery. |
PDF Full Text Request