P133. Measuring the radiographic efficacy of indirect decompression following minimally invasive lumbar interbody fusion: a computed tomography (CT) analysis study

Abstract

<h3>BACKGROUND CONTEXT</h3> The advancement of MIS techniques has led to increased reliance on indirect decompression techniques. The latest generation of MIS TLIF cages are typically expandable cages that restore disc height and achieve ligamentum flavum unbuckling with associated increased central canal area. While prior studies have measured the extent of indirect decompression associated with ALIF and LLIF, the degree of decompression achieved via MIS-TLIF has not been described. <h3>PURPOSE</h3> Assess the degree of indirect decompression following minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF). <h3>STUDY DESIGN/SETTING</h3> Single-center, multi-surgeon, retrospective review. <h3>PATIENT SAMPLE</h3> Patients undergoing MIS-TLIF without direct decompression between 3/2017 and 3/2021. Patients were included if they had a pre- and postoperative CT scan. <h3>OUTCOME MEASURES</h3> Pre- and postoperative CT scans were used to measure disc height, foraminal area (left and right) and central canal area at the operative level(s). The most recent postoperative patient reported outcome measures (PROMs) between 6 months and 2 years were used to compare against preoperative values. <h3>METHODS</h3> Postoperative CT was performed at 1-43 months based on surgeon-specific protocols. Both pre- and postoperative CT measurements were performed by two observers. PROMs were collected in a prospectively maintained database. Paired tests were used to compare changes in CT measurements and PROMs. Bivariate analysis was also done to assess correlations between the changes in CT measures and PROMs improvement. <h3>RESULTS</h3> A total of 40 patients (48 operative levels) were assessed; 16 (33.3%) of the subjects were female and 24 (50%) were male. The average age was 56.6 ± 15.9 years. The average length of follow-up was 17.9 ± 7.9 months for PROMs and 13.5 ± 9.3 months for postoperative CT imaging. There were 32 (80%) single-level and 8 (20%) two-level cases, with 23 (47.9%) operated at L4L5 and 25 (52.1%) at L5S1. Disc height, foraminal area, and central canal area all increased significantly (p < 0.001). Mean disc height increased 50%, from 4.2 to 6.3mm. Right sided foraminal area increased 23%, from 144 .5 to 177.8mm2, the left increased 21.4% from 142.8 to 173.4mm2, and the central canal increased 16.4% from 228.6 to 266 mm2. All PROMs except for SF12-MCS (p=0.439) showed a statistically significant improvement (p < 0.05). There was no correlation between each change in PROM and the increase in cross sectional canal area. <h3>CONCLUSIONS</h3> MIS-TLIF provides a significant degree of indirect decompression. Disc height, foraminal area and central canal area were all increased following insertion of the interbody cage via the MIS-TLIF technique. PROMs by 2 years demonstrated a statistically significant improvement. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.