1592. Immediate Restoration of Lordosis in Single-level Minimally Invasive Transforaminal Lumbar Interbody Fusion (MIS-TLIF): A Comparison of Static and Expandable Interbody Cages

Authors: Sertac Kirnaz; Christoph Wipplinger, MD; Franziska Schmidt, MD; Philip Saville, MD; Avani Vaishnav, MD; Rodrigo Navarro-Ramirez, MD; Sheeraz Qureshi, MD; Roger Härtl, MD (New York, NY)

Introduction: Sagittal alignment is becoming an increasingly important consideration in spine surgery. The literature is conflicted regarding the effect of MIS-TLIF on sagittal parameters and the role of expandable cage technology. We aimed to compare the lordosis generated by static and expandable cages in order to determine if there is a benefit of expandable cages in minimally invasive TLIF (MIS-TLIF) and determine what factors affect segmental lordosis and foraminal decompression. Methods: Pre-operative regional lordosis(RL), segmental lordosis(SL), and posterior disc height (PDH) were compared to post-operative values in patients undergoing single-level MI-TLIF using expandable or static interbody cages. Patients were stratified based on pre-operative SL: low lordosis (<15 degrees), moderate lordosis (15-25 degrees), and high lordosis (>25 degrees). Regression analyses were conducted to determine factors associated with post-operative SL and PDH. Results: 171 patients were included; 111 in the static and 60 in the expandable cohorts. Patients with low pre-operative lordosis experienced an increase in SL and maintained RL regardless of cage type. Those with moderate to high pre-operative lordosis experienced a decrease in SL and RL with the static cage but maintained SL and RL with the expandable cage. Although both cohorts showed an increase in PDH, the increase in the expandable cohort was significantly greater. Pre-operative SL was predictive of post-operative SL and pre-operative SL, pre-operative PDH and cage-type were predictive of post-operative PDH. Cage position was not related to postoperative SL or PDH. Conclusion: Expandable cages showed favorable results in restoring posterior disc height and maintaining lordosis in the immediate post-operative period. Cage position did not impact the restoration of lordosis or posterior disc height. Pre-operative segmental lordosis was the most significant predictor of post-operative segmental lordosis. Thus, pre-operative radiographic parameters and goals of the surgery should be important considerations in surgical planning.