Post-operative period increases the risk of DVT due to immobilization. Diagnosis of DVT: D-dimer measurement: If normal, no indication for fuher investigation but, if raised, a duplex ultrasound examination of the deep veins should be performed Duplex ultrasound: Filling defects in flow and lack of compressibility indicate the presence of a thrombosis . Ascending venography: Shows thrombus as a filling defect, is now rarely required .