675 Chemoprophylactic Anticoagulation Causes a Marked Decrease in Thromboembolic Events Following Lumbar Fusion: Causal Inferences from a Propensity-Matched Analysis of 1302 patients

Abstract

INTRODUCTION: Chemoprophylactic anticoagulation is commonly used to prevent venous thromboembolic events (VTE) after lumbar fusion. However, the magnitude of the associated risk reduction is not well described, and conventional retrospective statistical methods preclude causal inferences from this association. METHODS: 1302 consecutive lumbar fusions performed at our institution over a six-year period were identified, and relevant clinical and demographic data were collected. VTE events within 30 days postoperatively were identified. Patients who were given chemoprophylaxis and controls were matched according to age, body mass index, sex, Charlson Comorbidity Index, history of VTE, estimated blood loss, length of surgery, transfusion, whether surgery was staged, and whether surgery used an anterior approach. K-nearest neighbor propensity score matching was performed, and covariate adjustments were made to draw causal inferences regarding VTE rate. RESULTS: Unadjusted, there was no difference in the rate of VTE between patients who did (3.8%) and did notreceive chemoprophylaxis (4.4%, OR = 0.86 [0.47, 1.58], p = 0.667). On multivariable regression, and chemoprophylaxis was negatively associated with VTEs (OR = 0.38 [0.15, 0.95], p = 0.039). 589 lumbar fusion patients with and without chemoprophylaxis were successfully matched. After matching, median bias was 1.9%, and overall known bias was reduced by a median of 91.4%. After matching, covariates were well balanced (Rubin's B = 21.8). A covariate adjusted logistic regression model confirmed that chemoprophylaxis was associated with reduced odds of VTE (OR = 0.40 [0.16, 0.98], p = 0.044). The average treatment effect of chemoprophylaxis was a reduction in VTE of 3.7%. The only instance of epidural hematoma occurred in the control group. CONCLUSIONS: Among patients undergoing lumbar fusions, chemoprophylactic anticoagulation causes a marked decrease in VTE.