Hybrid pedicle screw and modified cortical bone trajectory technique in transforaminal lumbar interbody fusion at L4-L5 segment: finite element analysis.

Background: Investigate the biomechanical properties of the hybrid fixation technique with bilateral pedicle screw (BPS) and bilateral modified cortical bone trajectory screw (BMCS) in L4-L5 transforaminal lumbar interbody fusion (TLIF).

Methods:  Three finite element (FE) models of the L1-S1 lumbar spine were established according to the three human cadaveric lumbar specimens. 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) were implanted into the L4-L5 segment of each FE model. The range of motion (ROM) of the L4-L5 segment, von Mises stress of the fixation, intervertebral cage, and rod were compared under a 400-N compressive load with 7.5 Nm moments in flexion, extension, bending, and rotation.

Results:  BPS-BMCS technique has the lowest ROM in extension and rotation, and BMCS-BMCS technique has the lowest ROM in flexion and lateral bending. The BMCS-BMCS technique showed maximal cage stress in flexion and lateral bending, and the BPS-BPS technique in extension and rotation. Compared to the BPS-BPS and BMCS-BMCS technique, BPS-BMCS technique presented a lower risk of screw breakage and BMCS-BPS technique presented a lower risk of rod breakage.

Conclusion:  The results of this study support that the use of the BPS-BMCS and BMCS-BPS techniques in TLIF surgery for offering the superior stability and a lower risk of cage subsidence and instrument-related complication.