Cage’s Footprint on the Endplate Stresses Immediately Surgery: A Finite Element Based Study

INTRODUCTION Transforaminal Lumbar Interbody fusion (TLIF), using interbody cages is a popular surgical method of treating various spinal disorders. In the past few years, various types of interbody cages have been introduced to spine surgeons. These interbody device and footprint sizes [1]. The footprint size of the interbody device is an important factor that determines the biomechanical stability afforded by these implants. Moreover, occurrence of subsidence is also believed to be influenced by the footprint size of the device1. We hypothesized that a large footprint interbody would help distribute the endplate stresses over a wide surface area, leading to lower peak stresses. Such a device may reduce the occurrence of cage subsidence. For this purp Element (FE) analysis was conducted to compare the loading & stress at vertebral endplate following implantation with a AVID TLIF cage with a large foot print compared with regular TLIF cage in different configuration. METHODS A 3D, ligamentous, experimentally validated finite element model of L3-S1 lumbar segment [2] was used for this study. the AVID interbody cage as well as a regular TLIF cage and transferred into the FE model. Four different surgical cases shown in figure 1, were simulated which included: A) Double TLIF B) Symmetric TLIF c) Asymmetric TLIF and D)AVID TLIF device cage was placed inside the L4-L5 segment following a simulated surgical procedure which included a uniltaral total facet partial annulectomy and total nucleotomy. To simulate the surgical procedure for placement of the cage inside the segment, the lower vertebrae (L5) was fixed and the upper one (L4) was distracted until required intevertebral height was achieve placement of the cage, then a contact was defined between the cage and the vertebral endplate allowing settlement of the vertebral on the cage. A rough friction formulation was then simulated at the interface of cage with endplate and graft with endplate to simulate the rigid interface. The cages were assigned material property of PEEK (E=3400 MPa, v=0.3) and were filled with cancelous bone graft (E=100 v=0.2). A titanium (E=115 GPa, v=0.3) screw-rod fixation construct was added to the cage implanted segment. The rods were fixed to the screw heads and the screws were affixed to the pedicle bone.