The purpose of this study is to find the best possible (optimal) dose (effect versus adverse events) of YM150 to prevent the risk of blood clot formation after scheduled hip replacement surgery.

Inclusion Criteria:

• Scheduled for elective primary hip replacement
• Age 18 years or over
• Written informed consent obtained

Exclusion Criteria:

• Documented history or considered at increased risk of venous thromboembolism
• Subjects considered at increased risk of bleeding
• Surgery planned for contralateral hip at the same time or within 10 weeks after enrolment
• Concomitant use of anticoagulants/ antiplatelet agents