Optimal axis for lumbosacral interbody fusion: Prospective finite element analysis and retrospective 3D-CT measurement.

A feasible and optimal axis of biomechanical and anatomic significance in axial lumbosacral interbody fusion (AxiaLIF) was designed. Using the image dataset of an adult volunteer, two groups of finite element (FE) models of the AxiaLIF, lumbosacral anterior column fixation (ACF) models and middle column fixation (MCF) models with different bone graft fusion degrees, were prospectively established, and their biomechanical differences were comparatively predicted. In addition, 3D reconstruction was performed by retrospectively collecting CT data from pelvises in 60 adult cases. Their anatomic parameters relating to two groups of models were digitally measured and statistically compared. Numerical analysis revealed that the load and the maximum stress on the screw as well as the maximum stress difference between the screw and peripheral tissues in the MCF model were reduced compared with the ACF model. These indices of both models all decreased markedly in response to the increase in the disc fusion degree. Statistical analysis revealed that the effective fixed length of the sacrum in the MCF model was increased compared with the ACF model (P < 0.05). The surgical dissection distance of presacral vessels and nerves from the axis to sacrum of the MCF model was reduced compared with the ACF model (P < 0.05). The feasible and optimal axis of biomechanical and anatomic significance of the AxiaLIF is similar to the axis of the MCF model. Disc bone graft fusions plus axial screw fixations of middle column could strengthen the biomechanical stability of the AxiaLIF model. Clin. Anat. 32:337-347, 2019.