Spine and implant FE models used in this study. (A). The osseous structures, intervertebral discs, and ligaments of the intact spine. (B). The Awesome Dynamic Rod and Z-brace cage. (C). At the L4-L5 disc space, the Z-brace cage was placed obliquely with the left posterolateral corner of the annulus fibrosus removed as in PLIF procedures. (D). Four FE models used in this study.