Influence of Placement of Lumbar Interbody Cage on Subsidence Risk: Biomechanical Study

Lumbar spinal fusion is a common surgical procedure that can be done with a variety of different instrumentation and techniques. Despite numerous research studies investigating subsidence risk factors, the impact of cage placement on subsidence is not fully elucidated. This study aims to determine whether placement of an expandable TLIF cage at the center endplate or at the anterior apophyseal ring affects cage subsidence. A TLIF cage was placed centrally or peripherally between two synthetic vertebral models of L3 and L4. A compression platen attached to a 10 KN load cell was used to uniaxially compress the assembly. The ultimate force required for the assembly to fail and subsidence stiffness were analyzed. CT scans of each L3 and L4 were obtained and maximum endplate subsidence was measured in the frontal plane. Anterior apophyseal cage placement resulted in higher stiffness of the vertebrae-cage assembly (Ks , 962.89 N/mm) and a higher subsidence stiffness (Kb,987.21 N/mm) compared to central placement (p <0.05). Ultimate compressive load of the vertebrae-cage assembly did not increase. Moreover, the maximum subsidence depth did not significantly vary between placements. The subsidence stiffness increased with anterior apophyseal cage placement. Periphery endplate cortical bone architecture may play a role in resisting the impact of cage subsidence. To fully understand the effect of cage placement on cage subsidence, future studies should investigate its implications on native and diseased spine.