THE EFFECTS OF BONE MICROSTRUCTURE ON SUBSIDENCE RISK FOR ALIF, LLIF, PLIF, AND TLIF SPINE CAGES.

Several approaches (anterior, posterior, lateral, and transforaminal) are used in lumbar fusion surgery. However, it is unclear whether one of these approaches has the greatest subsidence risk as published clinical rates of cage subsidence vary widely (7-70%). Specifically, there is limited data on how a patient's endplate morphometry and trabecular bone quality influences cage subsidence risk. Therefore, this study compared the subsidence between anterior (ALIF), lateral (LLIF), posterior (PLIF), and transforaminal (TLIF) lumbar interbody fusion cage designs to understand the impact of endplate and trabecular bone quality on subsidence. Forty-eight lumbar vertebrae were imaged with micro-CT to assess trabecular microarchitecture. Micro-CT images of each vertebra were then imported into image processing software to measure endplate thickness and maximum endplate concavity depth. Generic ALIF, LLIF, PLIF, and TLIF cages made of PEEK were implanted on the superior endplates of all vertebrae and subsidence testing was performed. The results indicated that TLIF cages had significantly lower (p<0.01) subsidence stiffness compared to ALIF and LLIF cages. Maximum subsidence force for TLIF cages was also significantly lower (p<0.01) than other cage groups. For all cage groups, trabecular BVF was better correlated with maximum subsidence force compared to endplate thickness and concavity depth. These findings highlight the importance of cage design (e.g. surface area), placement on the endplate, and trabecular bone quality on subsidence. These results may help surgeons during cage selection for lumbar fusion procedures to mitigate adverse events such as cage subsidence.