EVALUATING VENOUS THROMBOEMBOLISM IN PATIENTS WITH METASTATIC BONE DISEASE: ARE WE TREATING PATIENTS WITH APPROPRIATE THROMBOPROPHYLAXIS?

Metastatic bone disease (MBD) has a substantial impact on quality of life in cancer patients. Despite the prevalence of MBD, the incidence of post-operative venous thromboembolism (VTE) including pulmonary embolism (PE) and deep vein thrombosis (DVT) remains high and is likely under-reported. Additionally, there is a paucity of guidelines for directing optimal thromboprophylaxis in this high-risk patient population. The primary objective of this study was to evaluate the use of thromboprophylaxis in patients with MBD undergoing orthopaedic surgery. The secondary objectives were to determine the incidence of VTE and identify risk factors for developing VTE post-operatively. We have conducted a retrospective, multicentre cohort study of adult patients presenting for orthopaedic surgery for MBD of the long bones or pelvis across nine hospitals between 2006 and 2021. All VTE events were identified through chart review and were defined as an image-confirmed diagnosis of a DVT or PE. Outpatient prescriptions for post-operative thromboprophylaxis or anticoagulation were obtained from the regional Pharmaceutical Information Network (PIN). The PIN data search included prophylactic and therapeutic dosages for low-molecular weight heparin and direct oral anticoagulants, as well as therapeutic dosages of warfarin prescribed up to 90 days post-operatively. A binomial logistic regression analysis was performed to identify risk factors for developing VTE. A total of 558 patients were included with a median age of 67.3 years and 52.0% of patients were female. Breast, lung, prostate, renal cell carcinoma, and multiple myeloma were the most common primary malignancies (n=461, 82.5%). Lower extremity surgery was more prevalent, with 487 patients (87.3%) undergoing surgery of the femur, tibia, or pelvis. The indication for surgery was a pathologic fracture in 344 patients (61.7%) and an impending fracture in 214 patients (38.4%). The average post-operative length of stay was 10 days (95%CI: 9–12). Median follow-up was 8.0 months (95%CI: 6.8–9.7). Outpatient thromboprophylaxis was prescribed in only 198 patients (35.5%). Median duration of thromboprophylaxis was 30 days (IQR: 10–60). Thirty-four (6.1%) patients were on anticoagulation for chronic medical comorbidities. The incidence of VTE was 5.7% in the entire cohort, and 6.0% in patients undergoing surgery of the lower extremity. There were 24 PEs and 11 DVTs diagnosed. Notably, 10 PEs and six DVTs occurred in patients who were prescribed thromboprophylaxis. VTE was diagnosed a median of nine days post-operative (IQR: 5–36). Lack of outpatient prescription of thromboprophylaxis and a pathologic fracture were identified as risk factors for developing a VTE on logistic regression (p = 0.025 and p = 0.028, respectively) while age, sex, primary malignancy, surgical technique, and fixation strategy were not significant. We have identified low rates of thromboprophylaxis prescribing in patients undergoing orthopaedic surgery for MBD with a high rate of VTE (5.7%). As patients underwent diagnostic investigations for a VTE based on clinical indications, the true rate of VTE may be greater. This research highlights the need for evidence-based guidelines to optimize post-operative protocols and improve patient care in this high-risk population.