275 patients undergoing unilateral total knee arthroplasty were randomized to receive spinal epidural anaesthesia, VenaFlow compression device, and enoxaparin or spinal epidural anaesthesia, VenaFlow compression device, and aspirin to prevent deep vein thrombosis. Enoxaparin and aspirin were taken for 4 weeks after surgery. Deep vein thrombosis was diagnosed through ultrasonography completed 3 to 5 days and 4 to 6 weeks after surgery. At the end of the 6 week study period, it was found that the rates of deep thrombosis experienced by the enoxaparin group (14.1%) and the aspirin group (17.8%) were not significantly different.