Low-molecular-weight heparin prophylaxis using dalteparin extended out-of-hospital vs in-hospital warfarin/out-of-hospital placebo in hip arthroplasty patients - A double-blind, randomized comparison

Background: No randomized trials have directly evaluated the need for exten ded out-of-hospital thromboprophylaxis for patients who have hip arthroplas ty in the United States or Canada. The uncertainty as to the need for exten ded prophylaxis in North American patients is complicated by early hospital discharge, resulting in a short thromboprophylaxis interval. Methods: To resolve this uncertainty, we performed a randomized double-blin d trial in 569 patients who underwent hip arthroplasty comparing the use of dalteparin: sodium started immediately before surgery or early after surge ry and extended out-of-hospital to an overall interval of 35 days with the use of warfarin sodium inhospital and placebo out-of-hospital. Results: For patients with interpretable venograms in the preoperative, pos toperative, and combined dalteparin groups, new proximal vein thrombosis ou t-of-hospital was observed in 1.3%, 0.7% (P=.04), and 1.0% (P=.02) of patie nts, respectively, compared with 4.8% in the in-hospital warfarin/out-of-ho spital placebo group. The respective overall cumulative frequencies of all deep vein thrombosis were 30 (17.2%) of 174 patients (P<.001), 38 (22.2%) o f 171(P=.003), and 68 (19.7%) of 345 (P<.001) in the dalteparin groups comp ared with 69 (36.7%) of 188 for the in-hospital warfarin/out-of-hospital pl acebo group. For proximal deep vein thrombosis, the respective frequencies were 5 (3.1%) of 162 (P=.02), 3 (2.0%) of 151 (P=.007), and 8 (2.6%) of 313 (P=.002) compared with 14 (9.2%) of 153. No major bleeding occurred during the extended prophylaxis interval. Conclusions: Extended dalteparin prophylaxis resulted in significantly lowe r frequencies of deep vein thrombosis compared with in-hospital warfarin th erapy. Despite in-hospital thromboprophylaxis, patients having hip arthropl asty in the United States and Canada remain at moderate risk out-of-hospita l. The number needed to treat provides a public health focus; only 24 to 28 patients require extended prophylaxis to prevent 1 new out-of-hospital pro ximal vein thrombosis. Recent studies demonstrate that asymptomatic deep ve in thrombi cause the postphlebitic syndrome; thus, extended out-of-hospital prophylaxis will lessen the burden to both the patient and society.