P18. Peri-incisional subcutaneous fat thickness is associated with infection after posterior lumbar surgery in obese patients: a propensity score matched retrospective study

Abstract

BACKGROUND CONTEXT Obesity has been associated with increased risk of infection after posterior lumbar surgery, but previous studies have failed to take factors such as body composition and fat distribution into consideration. PURPOSE To determine the role in body habitus and weight distribution on developing a surgical site infection (SSI) after posterior lumbar surgery in obese patients. STUDY DESIGN/SETTING Retrospective study with propensity score matching. PATIENT SAMPLE A total of 483 posterior lumbar surgeries in obese patients (BMI > 28, mainland China criteria) at two institutions from Jan 2010 to Dec 2016 were reviewed. OUTCOME MEASURES Peri-incisional anatomic features such as horizontal distance from the lamina to the skin surface, paraspinal muscles thickness, and thickness of subcutaneous fat at the surgical site, were determined through preoperative MRI/CT images. METHODS All patients (n = 21) who developed SSI were compared to a propensity score matched cohort of obese patients who did not have SSI. Demographics and clinical attributes were collected, as well as the peri-incisional anatomic features. Risk and ROC analysis were performed to investigate the association between peri-incisional anatomic features and SSI. RESULTS The BMI index is higher but without statistical significance in patients with SSI compared with that in patients without SSI (31.5 ± 2.4 kg/m2 versus 30.4 ± 1.7 kg/m2, p = 0.080). Patients with SSI showed greater subcutaneous fat thickness contrasted with patients without SSI (30.0 ± 5.0 mm versus 24.0 ± 5.4 mm, p 25 mm and subcutaneous fat thickness > 30 mm increased the risk of SSI by 1.9 (p = 0.011) and 3.0 (p=0.040), respectively. ROC analysis demonstrated subcutaneous fat thickness as a biomarker for SSI prediction (AUC = 0.82, 95% CI: 0.51 ∼ 0.85), with sensitivity and specificity of 76.2% and 81.0%, respectively. CONCLUSIONS Peri-incisional subcutaneous fat thickness is associated with a significantly increased risk of SSI after posterior lumbar surgery in obese patients. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.