The influence of oral anticoagulation therapy on deep vein thrombosis rates four weeks after total hip replacement.

Purpose: The purpose of this study was to assess the rate of postoperative deep vein thrombosis (DVT) as a function of oral anticoagulation therapy after total hip replacement surgery.

Methods: A total of 125 patients completed the study. All the patients received sequential gradient pneumatic compression over elastic stockings until hospital discharge. In addition, all the patients underwent postoperative heparin therapy followed by oral warfarin therapy, adjusted in dose to maintain a goal international normalized ratio (INR) level of 2.0 to 3.0. Warfarin therapy and compression stockings were continued for 1 month after surgery. Bilateral duplex scanning was performed 1 and 4 weeks after surgery to assess the rate of DVT.

Results: Nineteen of the 125 patients had DVT develop (15.2%). Of those thromboses, six (31.6%) and 13 (68%) were detected 1 week and 1 month after surgery, respectively. The rate of proximal DVT was 2.4% (3 of 125) 1 week after surgery and rose to 8.2% (10 of 122) 1 month after surgery. Most DVT cases (64%; 12 of 19) were asymptomatic. The patients in whom DVT developed had significantly lower INR values during the second to fourth postoperative weeks than did those patients without thrombosis, and no differences in INR values were found during the first postoperative week.

Conclusion: The risk of the development of DVT extends beyond hospital discharge in patients who undergo total hip replacement, despite a regimen of prolonged oral anticoagulation therapy. This is particularly true in patients whose INR values did not reach therapeutic range during the first postoperative month. Therefore, thrombosis prophylaxis regimens on the basis of the administration of warfarin should try to maintain INR values within therapeutic range during the entire first postoperative month to minimize the incidence of DVT.