Anterior approach lumbar fusions cause a marked increase in thromboembolic events: Causal inferences from a propensity-matched analysis of 1147 patients

Objective: Anterior lumbar fusions are thought to be associated with elevated venous thromboembolic event (VTE) rates, but the magnitude of this increase in VTE is not well described. The objective of this study was to quantify any increase in VTE caused by anterior approach lumbar fusion. Methods: 1147 consecutive lumbar fusions performed at our institution over a six-year period were identified, and clinical and demographic data were collected. K-nearest neighbor propensity score matching and propensity score adjusted regression were performed. Patients undergoing anterior versus posterior approach lumbar fusions were matched according to age, body mass index, sex, VTE history, estimated blood loss, length of surgery, transfusion, selection for postoperative intensive care unit (ICU) admission, comorbid disease burden, and use of chemoprophylactic anticoagulation. Results: Anterior approach surgery (OR=4.29, p < 0.001), a history of VTE (OR=8.67, p < 0.001), age (OR=1.53, p = 0.014), length of surgery (OR=1.16, p = 0.044), and selection for postoperative ICU admission (OR=4.60, p = 0.005) were independently associated with VTE on multivariable regression. 1058 anterior or posterior approach fusion patients were matched. After matching, overall bias was reduced by 71.0 %, no covariates remained significantly different between groups, and propensity scores were well balanced between populations (Rubin's B <= 0.25, 0.5 <= Rubin's R <= 2.0). Significantly more patients in the anterior group underwent lower extremity duplex ultrasonography (LED) (36.9 % vs. 14.8 %, OR=3.36 [2.38, 4.76], p < 0.0001), and a statistically insignificantly higher proportion of LEDs were positive among patients in the anterior group (23.2 % vs. 13.2 %, OR=1.99 [0.92, 4.25], p = 0.108). After matching, the rate of VTE was 8.6 % for the anterior group and 1.3 % for the posterior group, with anterior approach surgery causing an increase in VTE by 7.2 % (95 % CI [2.28 %, 12.16 %], p = 0.004). Conclusion: Among patients undergoing lumbar fusions, anterior approach surgery causes an increase in VTE by 7.2%, which is a multifold increase in the proportion of patients with thromboembolic complications.