Impact of Multiple Operative Levels on Radiographic Subsidence in Stand-Alone Lateral Lumbar Interbody Fusion.

Abstract

Lateral Lumbar Interbody Fusion (LLIF) is a useful minimally invasive technique for arthrodesis, yet subsidence is still a significant postoperative concern. This study aims to evaluate the impact of the number of operative levels on subsidence rates following LLIF. Patients who underwent LLIF procedures between 2014 and 2022 at two quaternary referral centers were reviewed. Collected variables included age, sex, BMI, smoking status, number of operative levels, cage material, average operative level bone density (Hounsfield units), and length of imaging follow-up. Two independent spine surgeons graded postoperative implant subsidence on postoperative imaging according to the Marchi criteria. 144 patients (218 surgical levels) met the inclusion criteria. Lateral plate fixation was utilized at 110 (50%) levels. Median imaging follow-up was 13 months [IQR: 11-29 months]. On univariate analysis, only PEEK cage material (p = 0.033) and the presence of lateral plating (p = 0.012) were significantly different between patients with and without subsidence; however, on multiple logistic regression, both lateral plating (p = 0.03) and increased number of operative levels (p = 0.047) were associated with decreased odds of subsidence, while age (p = 0.013) and PEEK cage material (p = 0.036) were associated with increased odds of subsidence. Multilevel stand-alone LLIF may reduce the rate of subsidence independent of other surgical factors such as lateral plating. Future biomechanical studies should be conducted to further determine the protective mechanism of multilevel LLIF.