1593. Immediate Restoration of Lordosis in Single-level Minimally Invasive Transforaminal Lumbar Interbody fusion (MI-TLIF): A comparison of Expandable and Static Interbody Cages

Authors: Avani Vaishnav; Philip Saville, MD; Steven McAnany, MD; Sertac Kirnaz, MD; Rodrigo Navarro-Ramirez, MD, MSc; Roger Hartl, MD; Catherine Gang, MPH; Sheeraz Qureshi, MD, MBA (New York, NY)

Introduction:
Current literature is conflicted regarding the effect of Minimally Invasive Tranforaminal Lumbar Interbody Fusion(MI-TLIF) on sagittal alignment and the role of expandable cage technology.

Objective:
To compare generation of lordosis by static and expandable cages, and determine what factors affect segmental lordosis and foraminal decompression.

Methods:
Segmental lordosis(SL), regional lordosis(RL) and Posterior Disc Height(PDH) were measured pre- and post-operatively on upright lateral radiographs of patients undergoing single-level MIS-TLIF with expandable or static cages. Distance from anterior edge of vertebral body to the front of the cage was measured. Based on pre-operative SL, patients were stratified into: low(<15o), moderate(15-25o) and high-lordosis(>25o). 

Non-parametric tests were used to compare radiographic parameters between static and expandable cages and the change from pre- to post-operatively. Linear regressions were conducted to assess the effect of pre-operative radiographic parameters, cage-type and cage-position on post-operative SL and PDH.

Results:
Of the 171 patients included; 111 were in the static and 60 in the expandable cohort. 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 PDH increased in both cohorts, 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 post-operative SL or PDH.

Conclusion: 
Expandable cages showed benefit in restoring disc height and maintaining lordosis in the immediate post-operative period. Cage position did not impact lordosis or 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.