Summary and conclusions A prospective study of patients undergoing total knee replacement was carried out by using a combination of 15I-fibrinogen scanning and phlebography, and showed a high incidence of venous thromboembolic disease (TE). Ventilation-perfusion lung scanning was performed to detect pulmonary emboli in most patients. High doses of aspirin and an intermittent low-pressure pneumatic compression device (IPCD) were effective, even in women, in preventing TE. Low doses of aspirin and placebo were equally ineffective in preventing TE. Lung-scan abnormalities compatible with pulmonary emboli were found in six out of 10 patients with isolated calf-vein thrombi. Conventional tests of platelet function did not predict the development of TE. No significant differences were found between the patients receiving low and high doses of aspirin with respect to the mean template bleeding time or platelet aggregation in response to adenosine diphosphate, collagen, and epinephrine, although these variables were significantly abnormal in the two groups receiving aspirin compared with those treated with placebo and the IPCD.Thus high doses of aspirin and a new low-pressure IPCD were effective in preventing venous TE in patients (predominantly women) undergoing total knee replacement. IntroductionVenous thromboembolism (TE), a common complication of orthopaedic surgery,1-3 is also a major cause of postoperative death.4 Although effective prophylaxis with low-dose heparin is feasible in many patients, its efficacy in those undergoing orthopaedic surgery remains controversial5 6 and is compounded by bleeding complications.6 Controversy exists regarding the effectiveness of aspirin as a mode of prophylaxis in venous TE,7 particularly in women.' We conducted a pilot study, which showed a high incidence of TE (about 800o) in patients undergoing total knee replacement at our hospital.9 Patients with a mean intake of 3 5 g aspirin/day had a significantly lower incidence of TE than patients who had not ingested any aspirin. We report here a prospective study designed to evaluate the efficacy of a low dose of aspirin (325 mg thrice daily), a high dose of aspirin (13 g thrice daily), and an intermittent lowpressure pneumatic compression device (IPCD) as compared with placebo (one tablet thrice daily) in preventing TE in patients undergoing total knee replacement.

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Manuscript received July 15, Il)l)l); accepted July 30, Il)l)l).