Bicortical Lateral Plate Screw Placement Reduces Subsidence Risk in Patients Undergoing Lateral Lumbar Interbody...

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 2 quaternary referral centers from 2014 to 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.