As Dr. Pedell points out, the mean length of stay after total hip or knee arthroplasty has decreased since we completed our study. Our study showed that an average of 10 days of warfarin prophylaxis given in the hospital only provided safe and effective patient care. With current lengths of hospital stay after joint arthroplasty as short as 4 days, the question is raised about whether outpatient warfarin treatment is warranted to ensure that patients receive prophylaxis for at least 10 days.

Our study does shed some light on this matter. We agree with Dr. Pedell that the state of mobilization at the time of hospital discharge is likely to be a factor in the risk for the development of postdischarge venous thromboembolism. At hospital discharge, 85% of the patients in our study were "fully mobile," and no correlation was observed between length of stay and risk for subsequent postdischarge venous thromboembolism. About 15% of the patients were discharged from the hospital before day 6. On the basis of this information, we believe that patients who receive prophylaxis for 5 days and are fully mobile at hospital discharge on day 5 do not require postdischarge prophylaxis. Postdischarge prophylaxis lasting up to 5 days should be considered for patients discharged on day 5 who are not fully mobile.

As stated by Dr. Rajput and Mr. Nanavati, controlled studies have shown that prolonging prophylaxis 3 weeks beyond hospital discharge reduces the rate of venography-confirmed deep venous thrombosis after total hip arthroplasty [1, 2]. However, it is uncertain whether prolonging prophylaxis for this length of time results in a clinically important reduction in the rate of symptomatic or fatal thromboembolic complications after total hip or knee arthroplasty. In the absence of outcomes data from controlled trials, the potential benefits of outpatient prophylaxis must be carefully weighed against the risks and the costs of medication and monitoring in any individual patient.