Prevention of venous thromboembolism in orthopedic surgery with vitamin K antagonists: a meta-analysis

The benefit-to-risk ratio of vitamin K antagonists (VKA), relative to active comparators, especially low-molecular-weight heparins (LMWH), for preventing venous thromboembolism in patients undergoing major orthopedic surgery is debated.

We performed a meta-analysis of all randomized trials in orthopedic surgery comparing adjusted doses of VKA to control treatments.

An exhaustive literature search, both manual and computer-assisted, was performed. Studies were selected on the basis of randomization procedure (VKA vs. a control group). At least one of the following outcome measures was to be evaluated: deep vein thrombosis (DVT), pulmonary embolism (PE), death, major hemorrhage or wound hematoma. Four reviewers assessed each article to determine eligibility for inclusion and outcome measures.

VKAs were more effective than placebo or no treatment in reducing DVT [567 patients, relative risk (RR) = 0.56, 95% confidence interval (CI) 0.37, 0.84, P < 0.01] and clinical PE (651 patients, RR = 0.23, 95% CI 0.09, 0.59, P < 0.01). These results were obtained at the cost of a higher rate of wound hematoma (162 patients, RR = 2.91, 95% CI 1.09, 7.75, P = 0.03). VKAs were also more effective than intermittent pneumatic compression (534 patients, RR = 0.46, 95% CI 0.25, 0.82, P = 0.009) in preventing proximal DVT. In contrast, VKAs were less effective than LMWH in preventing total DVT and proximal DVT (9822 patients, RR = 1.51, 95% CI 1.27, 1.79, P < 0.001; and 6131 patients, RR = 1.51, 95% CI 1.04, 2.17, P = 0.028, respectively). The differences between VKA and LMWH in major hemorrhage and wound hematoma were not significant.

In patients undergoing major orthopedic surgery, VKAs are less effective than LMWH, without any significant difference in the bleeding risk.