65. Subsidence after minimally invasive transforaminal lumbar interbody fusion with expandable cage: Rates and clinical impact

Abstract

<h3>BACKGROUND CONTEXT</h3> Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is commonly used to treat lumbar spinal stenosis with degenerative disc disease. Expandable cage technology has been increasingly adopted and has demonstrated successful results, offering a larger footprint and intraoperative height adjustment, enabling more precise dialing in of sagittal alignment and disc height. While many advances have been made, endplate violation and postoperative cage subsidence can still be seen. <h3>PURPOSE</h3> To determine the rate and clinical implications of subsidence after expandable cage use in MI-TLIF. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study. <h3>PATIENT SAMPLE</h3> Patients undergoing MI-TLIF for degenerative disc disease using articulating, expandable cages. <h3>OUTCOME MEASURES</h3> Patient-reported outcome measures (PROMs), including the Oswestry Disability Index (ODI), visual analog scale (VAS) for back/leg pain, Short Form-12 (SF-12), and PROMIS physical function (PF). <h3>METHODS</h3> Patients undergoing MI-TLIF for degenerative disc disease using articulating, expandable cages from 2017-2019 were retrospectively studied. AP and lateral radiographs were reviewed and evaluated for the presence or absence of subsidence intraoperatively and at follow-up times including 2 weeks, 6 weeks, 12 weeks, 6 months and 1 year postoperatively. Each of the four corners of the implant was evaluated, and subsidence was determined to have occurred if there was endplate violation ≥3mm at any corner. Patient-reported outcome measures, including the ODI, VAS for back/leg pain, SF-12 and PROMIS PF were recorded at the preoperative and follow-up time points. Fusion was assessed 1-year postoperatively via CT. <h3>RESULTS</h3> A total of 87 patients were included, with mean age 58.3 years (SD,13.4). Of 87 total patients, 13 (14.9%) demonstrated subsidence, with the majority (84.6%) of cases occurring within the first 12 weeks. Patients who had subsidence were older (67.2 vs 56.7 yrs; p=0.009), had lower bone quality (p=0.049), and were more likely to have 2-level surgery compared to those without (p=0.032). On multiple regression analysis, age was the only variable which retained significance when comparing the subsidence and no subsidence groups (p=0.04). There were significant differences in subsidence rate with greater implant height (p=0.013) and smaller width (p=0.026). With the exception of SF-12 PCS at 1-year postoperative, there were no significant differences in any patient-reported outcomes between the 2 groups. The overall fusion rate was 90.5% (57/63 levels) at 1-year postoperative, with no significant difference in fusion rate between the subsidence and no subsidence groups. <h3>CONCLUSIONS</h3> The rate of subsidence after MI-TLIF was 14.9%, with the majority of cases occurring within the first 12 weeks postoperatively. Patients who had subsidence were older with lower bone quality, had cages with greater height and smaller width, and were more likely to have 2-level surgery. With the exception of SF-12 PCS at 1 year, there were no significant differences in any of the PROMs between the groups. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.