Risk of deep-venous thrombosis after hospital discharge in patients having undergone total hip replacement: double-blind randomised comparison of enoxaparin versus placebo.

Background: The risk of deep-vein thrombosis (DVT) and pulmonary embolism after total hip replacement (THR) surgery may persist after hospital discharge, but the extent of the risk is not known. We carried out a single-centre, prospective, randomised, double-blind trial with the aims of quantifying this risk and assessing the efficacy of continued prophylactic treatment.

Methods: At hospital discharge 13-15 days after surgery, we recruited 179 consecutive THR patients who had no DVT visible on bilateral ascending venography of the legs. The patients were randomly assigned subcutaneous enoxaparin (40 mg, once daily; n = 90) or placebo (n = 89) for 21 (19-23) days. The primary endpoint was the occurrence of DVT or pulmonary embolism. Venography was repeated at the end of 21 days' treatment or earlier if necessary.

Findings: There were no deaths and no symptomatic pulmonary embolisms during the study or follow-up periods. Of 173 patients with evaluable venograms, intention-to-treat analysis of efficacy showed that the rate of DVT at day 21 after discharge was significantly lower in the enoxaparin group than in the placebo group (6 [7.1%] vs 17 [19.3%], p = 0.018). Distal DVT was detected in one (1.2%) patient in the enoxaparin group and in ten (11.4%) patients in the placebo group (p = 0.006). Proximal DVT was observed in five (5.9%) patients in the enoxaparin group and in seven (7.9%) patients in the placebo group (p = 0.592). A perprotocol analysis of efficacy in 155 patients confirmed these findings. Safety was good; three minor bleeding episodes occurred in the enoxaparin group and one in the placebo group, but none of these episodes necessitated withdrawal from the study.

Interpretation: In patients who have undergone THR surgery, are without venogram-proven DVT at hospital discharge, and do not receive antithrombotic prophylaxis after discharge, the risk of late-occurring DVT remains high at least until day 35 after surgery. Continued prophylaxis with enoxaparin is effective and safe in reducing this risk.