72. Static vs expandable TLIF cage: a comparison of predicted and achieved restoration of intervertebral disc height

Abstract

<h3>BACKGROUND CONTEXT</h3> In situ expandable TLIF cages have been shown effective in restoration of intervertebral disc and neuroforaminal height in minimally invasive surgery. However, prior studies have reported increased rates of radiographic subsidence with expandable cages, in part, related to presumed increased stress per surface area at the graft-bone interface upon distraction. A novel multidirectional expandable TLIF cage aims to increase axial fusion footprint to better distribute this stress and reduce subsidence. However, the relationship between predicted and actual disc height (DH) restoration upon physiologic loading between a static and expandable cage following MIS TLIF remains unclear. <h3>PURPOSE</h3> To evaluate and compare the predicted vs actual DH restoration following MIS TLIF using an expandable vs static cage. <h3>STUDY DESIGN/SETTING</h3> A single-center retrospective review of 137 consecutive adult patients undergoing 1- or 2-level MIS TLIF were divided between an expandable cage cohort (ECC, n=83) vs static caged cohort (SCC, n-54). Predicted DH restoration was calculated based on cage height. DH was assessed by upright X-ray before, immediately following and one year postsurgery. <h3>PATIENT SAMPLE</h3> A single-center retrospective review of 137 consecutive adult patients undergoing 1- or 2-level MIS TLIF. <h3>OUTCOME MEASURES</h3> Predicted DH restoration was calculated based on cage height. DH was assessed by upright X-ray before, immediately following and one year postsurgery. <h3>METHODS</h3> A single-center retrospective review of 137 consecutive adult patients undergoing 1- or 2-level MIS TLIF were divided between an expandable cage cohort (ECC, n=83) vs static cage cohort (SCC, n-54). Predicted DH restoration was calculated based on cage height. DH was assessed by upright X-ray before, immediately following and one year postsurgery. <h3>RESULTS</h3> One hundred thirty-seven patients representing 148 operative levels (mean age 63.7±11.3 years, 57.7% female) were included for analysis. Mean cage height in the SCC vs ECC was 10.3±1.6 mm and 10.8±1.7 mm, respectively. Preoperative mean DH were comparable at 7.1±0.3 mm and 7.6±0.2 mm in the SCC and ECC (p>0.05). A statistically significant difference in mean DH restoration favoring the ECC was obtained immediate postoperative with durable gains to 1-year postoperative (p0.05) <h3>CONCLUSIONS</h3> The expandable TLIF cage studied showed significantly better gains in DH restoration at the immediate postoperative to one year post surgery. At one year, significantly more patients maintained at least their predicted DH in the ECC, suggestive that an expandable cage may restore, maintain and achieve predicted DH better than a static cage following MIS TLIF. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.