Comparing an instrumented posterior fixation system with rigid and semi-flexible rods using finite element analysis

In this study finite element model of the human lumbar spinal segments (L2–L5) was developed to parametrically examine the stiffness of a dynamic stabilization device and its influence on the mobility of adjacent intervertebral segments. Five models were analyzed and compared: (1) a lumbar spine with intact discs, a reference; (2) a fused spine with a fixation device following interbody fusion and total laminectomy; (3) a spine stabilized with a dynamic stabilization device following total laminectomy; and (4) an additional vertically parallel paired dynamic posterior fixator and paired rigid fixator implemented at levels L3–L5. The disc pressure on the adjacent segments in the fused spine was greater than that of the intact spine, but the disc pressure of the dynamically stabilized spine was similar to that of the intact spine. The use of dynamic stabilization devices restored functionality more closely to that of the intact spine compared to the fused spine. The stiffness values utilized in the device were determined to be important design parameters for manufacturing dynamic stabilization devices.