Maximum subsidence of a centrally vs. peripherally placed transforaminal lumbar interbody fusion cage: A CT analysis using synthetic composite vertebral bodies

Hypothesis: The central placement of an interbody device will result in less subsidence
Study design: Subsidence study using CT imaging, following failure of a centrally versus peripherally placed TLIF cage

Introduction: Spinal fusion procedures are widely adopted for treatment of multiple spinal pathologies. They commonly involve the insertion of an interbody cage to restore the intervertebral height and permanently fuse the anterior and posterior vertebral bodies while also allowing for indirect decompression. Due to a variety of intra-operative factors, cage placement is not always center-center in the disc space. One of the major surgical complications of a spinal fusion is cage subsidence. To our knowledge, the influence of cage placement on cage subsidence has not been fully elucidated. Therefore, this study aims to evaluate whether a central or peripheral placement of a transforaminal lumbar interbody fusion (TLIF) cage influences the risk of subsidence.

Methods: A TLIF cage was placed centrally or peripherally between two synthetic composite vertebral models of L3 and L4. The vertebral column assembly was uniaxially compressed at constant speed until failure using an Electromechanical Testing System (Instron Model 5566, Norwood, MA). Computed tomography (CT) scans of each sample L3 and L4 were obtained using a CT scanner (nanoScan® PET/CT Mediso, USA) after mechanical testing. CT images were analyzed using Osirix 13.0.1. Maximum subsidence depth of both L3 caudally and L4 rostrally were measured in the coronal plane. Total area of failure in L3 and L4 was also measured in the axial plane.

Results: The maximum subsidence depth did not significantly vary between the centrally and peripherally located cage in both L3 and L4 (p=0.83, 0.77). While the area of failure in the vertebral body did not vary between central and peripheral placement, L3 vertebrae had significantly less subsidence compared to L4 in the axial plane (p <.01).

Conclusions: The risk of subsidence between central and peripheral cage placement may be lower than previously anticipated. While cage placement did not affect maximum subsidence or the area of vertebral deformation, L3 deformed in a smaller area than L4 in both groups.