Low-molecular-weight heparin (LMWH) is not effective at preventing symptomatic venous thromboembolism (VTE) in patients who are immobilized due to leg casting or have undergone knee arthroscopy, according to a new study from the Netherlands. In two trials, 1,543 patients who underwent arthroscopy and 1,451 patients who were immobilized after casting were randomized to eight weeks of LMWH (arthroscopy) or LMWH for the full duration of immobilization (casting) in a randomized, controlled fashion. In arthroscopy patients, VTE occurred in five of the 731 patients (0.7%) in the treatment group and in three of the 720 patients (0.4%) in the control group (relative risk [RR], 1.6; 95% confidence interval [CI], 0.4-6.8). Major bleeding occurred in one patient (0.1%) in the treatment group and in one patient (0.1%) in the control group. In the casted patients, VTE occurred in 10 of the 719 patients (1.4%) in the treatment group and in 13 of the 716 patients (1.8%) in the control group (RR, 0.8; 95% CI, 0.3-1.7). No major bleeding events occurred. The authors concluded that LMWH is not effective at preventing VTE after knee arthroscopy or for patients treated during the full period of immobilization due to casting. (Published online Dec. 3, 2016, doi: 10.1056/NEJMoa1613303).