Three-dimensional analysis of interbody cage-apophyseal ring contact to predict endplate subsidence following transforaminal interbody fusion

BACKGROUND: There is a higher risk of subsidence following transforaminal lumbar interbody fusion (TLIF) relative to other approaches. Decreased subsidence risk is associated with anterior cage placement, speculated to be because of increased apophyseal ring contact. However, this hypothesis is largely based on in vitro evidence and, to date, has not been investigated in a clinical cohort. METHODS: Pre-operative and post-operative computed tomography (CT) images from 42 TLIF patients were used to segment the endplate and cages. The apophyseal ring boundary was manually landmarked for each endplate. The pre-operative endplates were rigidly registered with the post-operative cage position, and an iterative closest point approach was used to calculate the contact area between the cage, apophyseal ring, and endplate. Subsidence was categorised based on severity (No Subsidence: