Lower limb trauma requiring immobilization is a very frequent condition that is associated with an increased risk of developing venous thromboembolism (VTE). The TRiP(cast) score has been developed to provide individual VTE risk stratification and help in thromboprophylactic anticoagulation decision. The recent CASTING study had confirmed that patients with a TRiP(cast) score \<7 have a very low risk of VTE and could be safely manage without prophylactic treatment. Conversely, patients with a score ≥ 7 have a high-risk of VTE and require a prophylactic anticoagulant treatment. Low molecular weight heparins (LMWH) have been shown to be effective in this indication. However, in the CASTING study, the 3-month symptomatic VTE rate was 2.6% in this subgroup despite LMWH prophylactic treatment. This result suggests that LMWH are not sufficiently effective in this particular subgroup of high-risk patients. Direct oral anticoagulants, and in particular rivaroxaban, may be an effective and safe alternative to LMWH. In the PRONOMOS study, comparing LMWH with rivaroxaban in patients who had undergone non-major lower limb surgery, the relative risk of symptomatic VTE was 0.25 (95% CI = 0.09 - 0.75) in favor of rivaroxaban 10mg. No significant increase in bleeding was found. In addition, as LMWH treatment requires subcutaneous daily injections, the use of rivaroxaban may positively impact patients' quality of life as well as being effective in medico-economic terms. The aims of this study are to demonstrate that rivaroxaban is at least as effective, easier to use and more efficient than LMWH in patients with trauma to the lower limb requiring immobilisation and deemed to be at risk of venous thromboembolism (TRiP(cast) score ≥ 7). High-risk patients are randomized to receive either rivaroxaban or LMWH. They are followed up at 45 days and 90 days to assess the occurrence of thrombotic events or bleeding, as well as their satisfaction with the treatment received.