Subcutaneous Lumbar Spine Index (SLSI) as a Risk Factor for Surgical Site Infection After Lumbar Fusion Surgery: A Retrospective Matched Case–Control Study

Abstract

Study Design: A retrospective matched case–control study. Objective: This study aims to investigate the value of Subcutaneous Lumbar Spine Index (SLSI) as a predictor of early surgical site infection (SSI) after lumbar intervertebral fusion surgery. Methods: A retrospective case–control study was performed on patients who underwent transforaminal lumbar interbody fusion (TLIF) from January 1, 2014 to December 31, 2019 in a single institution. Cases were defined as those who developed early SSI according to the US Center for Disease Control and Prevention criteria, and controls were matched from those patients without early SSI using the following matched criteria: gender, age, time of surgery and diabetes. Subcutaneous fat thickness (SFT) and SLSI were measured on preoperative MRI mid-sagittal T2 weighted images. Results: A total of 3615 patients who underwent TLIF were enrolled in this study. Thirty-three patients were included in early SSI, and sixty-six patients were selected as matched controls. Univariate analysis indicated that fusion levels (P =.007), operation time (P =.022), obesity (P =.013), SFT (P =.002) and SLSI (P =.001) were significantly associated with early SSI. Multiple logistic regression analysis revealed that multilevel fusion levels (P =.021), obesity (P =.035), a large SFT (P =.026) and a high SLSI (P =.012) were independent risk factors. Body mass index (BMI) and SLSI were moderately correlated (r2 =.55). ROC curve demonstrated that SLSI was more sensitive than SFT to predict the early SSI. Conclusion: SLSI is a novel radiological risk factor for early SSI development and is a better indicator than SFT to predict early SSI risk after lumbar intervertebral fusion.