Comparison of inpatient versus post-discharge venous thromboembolic events after spinal surgery: A single institution series of 6869 consecutive patients

Study design: retrospective chart review. Objective: We aimed to determine the perioperative risk factors that lead to inpatient or post-discharge venous thromboembolism (VTE) events after spinal surgery. Summary of background data: While many studies relate the risk factors in a post-surgical setting to the incidence of VTE, this study aims to separate these VTE into inpatient and post-discharge categories to examine timing and risk factors. Methods: We analyzed 6869 patients from 2009 to 2015 using Current Procedural Technology codes from a single tertiary academic institution. Patients were stratified based on occurrence and setting of VTE then controlled for perioperative characteristics with exclusion criteria being patients undergoing minor spine surgeries or secondary procedures. Results: In 170 VTE events, these factors were associated with increased risk for: Inpatient DVT only: IVC filter (OR 6.380 [3.414−11.924]), longer length of hospital stay (OR 1.083 [1.047−1.120]), a prior history of DVT (OR 3.640 [1.931−6.856]). Post-discharge DVT only: history of PE (OR 45.142 [6.785−300.351]), having a corpectomy (OR 26.670 [3.477−204.548]), and having an osteotomy (OR 18.877 [1.129−315.534]). Inpatient PE only: surgery >4 h (OR 30.820, p < 0.001), fracture (OR 6.913, p = 0.004), IVC filter (OR 3.135, p = 0.029). Post-discharge PE only: corpectomy (OR 541.271, p = 0.009), foraminotomy (OR 40.137, p = 0.013), EBL > 500cc (OR 2467.798, p = 0.002). Time to onset of VTE events was significantly longer for patients undergoing osteotomy (7.43 days) than for patients with fracture (4.28 days), which is consistent with our findings that fracture was an independent predictor of inpatient VTE, and osteotomy was an independent predictor of post-discharge VTE (p = 0.018). Conclusions: Time-to-VTE varies between types of surgeries. Some risk factors are independently associated with VTE at all times during the 30-day postoperative period, while other factors are only associated with either inpatient or post-discharge VTE. Those patients with high-risk features for post-discharge VTE merit increased study for thromboprophylaxis management.