Bicortical lateral plate screw placement reduces subsidence risk in patients undergoing lateral lumbar interbody fusion.

Abstract

Lateral Lumbar Interbody Fusion (LLIF) is an effective, minimally invasive option to decompress the neural elements; however, subsidence remains a risk postoperatively. The objective of this study is to analyze the effect of lateral plate screw placement techniques on postoperative subsidence. A retrospective review was conducted at two quaternary referral centers from 2014-2022. Radiographic subsidence, bony fusion, and screw length were measured on follow-up imaging. Continuous and categorical variables were compared with two-sided independent-samples T-tests and Chi-squared/Fisher's exact test, respectively. Multiple logistic regression was conducted to analyze factors associated with subsidence risk. A total of 144 patients with 218 operative levels were included. Mean age was 69 ± 11, 59% of the cohort was female, and 10% were active smokers. Median imaging follow-up was 13 [IQR: 11-29] months. Of the 218 operative levels, 27 (12%) experienced grade I or II subsidence. On univariate analysis, there was a statistically significant difference in subsidence rates based on cage material type (p = 0.033), presence of lateral plating (p = 0.012), number of operative levels (p = 0.034), and lateral plate screw type (p = 0.023). On multivariate analysis, bicortical screws (OR: 0.291 95% CI: 0.087-0.803, p = 0.016) reduced odds of subsidence, while unicortical screw (OR: 0.402, 95% CI: 0.098-1.267, p = 0.125) did not reduce odds of subsidence compared to no lateral plating. Based on these results, bicortical screw placement may be a protective factor against subsidence.