Thromboembolic and Bleeding Outcomes of Extended Duration Low-Intensity Warfarin Following Elective Total Knee Arthroplasty

•We identified 1487 patients receiving low-intensity warfarin after TKA•Time in therapeutic range (INR 1.5 to 2.5) was 55%•Symptomatic VTE occurred in 1.3% (95% CI 0.8%-2.0%) within 90 days•Most VTE occurred within 14 days of surgery (84.2%)•Clinically-relevant bleeding occurred in 1.7% (95% CI 1.1%-2.0%)

IntroductionThe purpose of this study was to describe the incidence of symptomatic venous thromboembolism (VTE), clinically-relevant bleeding, and death among a real-world population receiving warfarin prophylaxis targeting an international normalized ratio (INR) of 1.5 to 2.5 for four weeks following total knee arthroplasty (TKA).Materials and MethodsThis retrospective, observational study included patients receiving warfarin following a TKA between August 1, 2005 and July 31, 2009 identified in the Kaiser Permanente Total Joint Replacement Registry. Patients < 18 years, receiving warfarin for another indication, or without continuous KPCO membership during the study period were excluded.ResultsThere were 1487 patients with TKA included in the analysis. Mean patient age was 67.7 years and 61.7% were female. The median percent of time in therapeutic INR range during follow-up was 55% (interquartile range = 35%-75%). Nineteen cases of symptomatic VTE [1.3%; 95% confidence interval (CI) 0.8%-2.0%] including ten pulmonary emboli (PE) (0.7%) were identified within 90 days of surgery. Clinically-relevant bleeding occurred in 1.7% (95% CI 1.1%-2.5%) of patients during warfarin prophylaxis and there were no deaths within 90 days of surgery.ConclusionsThe rates of symptomatic VTE and clinically-relevant bleeding following TKA in patients receiving warfarin prophylaxis with a target INR of 1.5 to 2.5 were low. Additional studies should include low-intensity warfarin to identify the regimen that optimally balances risks of bleeding and symptomatic VTE after major orthopedic surgery.