Inclusion Criteria:

• Age > 16 years

• Unilateral or bilateral, closed or open, fractures of the lower extremity distal to the knee including:

  1. Isolated fractures of the tibia including tibial plateau, shaft and plafond and medial malleolus
  2. Isolated fractures of the fibula including fibular head, fibular diaphysis,distal fibula and lateral malleolus
  3. Combined fractures of the tibia and fibula
• Tibia and/or fibula fractures may be accompanied by fractures of the patella and/or foot as well as ligamentous injuries as long as either the tibia or the fibula is involved
• Patients must be scheduled to undergo surgery (internal or external fixation) for repair of their fracture during the current admission

Exclusion Criteria:

• Patients presenting greater than 72 hours after injury
• Major injury involving other site(s)
• Lower extremity vascular injury requiring surgical repair
• Known systemic bleeding disorder or INR > 1.5, aPTT > 40 sec, or platelets < 50 x 109/L at baseline
• Active, uncontrolled bleeding (as determined by the attending surgeon or delegate)
• Intracranial or other major bleed in the previous 4 weeks
• Ongoing need for anticoagulation for other reasons
• Previous DVT or PE (objectively proven or treated with anticoagulants)
• Known molecular hypercoagulable state
• Active cancer
• Inability to receive contrast dye because of pregnancy, contrast allergy, or renal failure (serum creatinine > 300 mmol/L)
• Hypersensitivity to heparin or LMWH (including history of HIT)
• Inability to arrange out-of-hospital study medication administration
• Anticipated inability to undergo endpoint duplex ultrasound or follow-up (day 14 ± 2, 6 weeks, 3 months)
• Inability or refusal to provide informed consent· Previous participation in this study
• Estimated weight less than 40 kg