Comparative Finite Element Analysis of Lumbar Cortical Screws and Pedicle Screws in Transforaminal and Posterior Lumbar Interbody Fusion

Objective: Lumbar cortical screw fixation (CSF), rather than pedicle screw fixation (PSF), has recently been attempted in lumbar interbody fusion. The purpose of our study was to evaluate the biomechanical stability of lumbar CSF using a finite element (FE) model. Methods: A 3-FE model, including the L1 to S1 levels, was designed to evaluate and compare the biomechanical stability of lumbar CSF and PSF in single-level lumbar interbody fusion at L4-5. Cortical or pedicle screws were inserted bilaterally, and posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) were modeled at L4-5, respectively. We compared the stability of CSF to that of PSF in these 2 different anatomic variations of PLIF, as well as in TLIF. Results: Lumbar CSF showed less stability than PSF in PLIF when the midline posterior ligaments were not preserved, but demonstrated similar stability when the ligaments were preserved. The range of motion (ROM) at the treated level in CSF was larger than that observed for PSF, in all PLIF and TLIF models. Furthermore, the ROM in the posterior ligament-sacrificing PLIF with CSF model was larger than the ROM in the posterior ligament-preserving PLIF with CSF or PSF model. Conclusion: Based on our FE analysis, the stability of CSF is comparable to that of PSF in PLIF and TLIF when the midline posterior ligaments are preserved.