After hip or knee replacement all patients receive a standardized treatment with blood thinners, this medication is called thrombosis prophylaxis. However, despite this standard treatment some individuals still develop venous thrombosis (VTE), while others experience bleeding. This indicates that not all patients have the same VTE risk following surgery. Individualizing the amount of thrombosis prophylaxis following surgery might lead to less thrombotic and bleeding events. In this study the investigators individualize the treatment with thrombosis prophylaxis based on the medical history of a patient. The main questions this study aims to answer are: Can thrombosis prophylaxis be shortened in patients with a low VTE risk to decrease the risk of bleeding without increasing the risk of VTE? Does an increase in the dose and duration of thrombosis prophylaxis in patients with a high VTE risk reduce the risk of VTE without inducing an unacceptable risk of bleeds? Researchers will compare both the shortened treatment in low VTE risk patients and the intensified and extended treatment in high VTE risk patients with the standard treatment to assess the risk of VTE and bleeding in comparison to the standard treatment. Participants will receive 4 questionnaires to evaluate whether they have experienced a VTE or bleed. For this study no additional hospital visits are necessary.