DVT in Orthopedic and Abdominal surgery patients - is due to different types of pathophysiological changes?

Why should there be a difference in the incidence of DVT in Orthopedic and abdominal surgery patients in post operative period?

Lower preoperative fibrinolytic activation observed in patients undergoing orthopedic surgery compared with abdominal surgery might have pathophysiological consequences. This may explain why Without prophylaxis, patients subjected to major abdominal surgery have a risk of deep vein thrombosis of approximately 30%, while the rate varies between 40% and 60% in orthopedic surgery. Pinjala R K

http://link.springer.com/article/10.1007/BF02912463