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was 130.1 ± 34.9 min (range, 115-158 min). All surgeries were performed under general anes-thesia. Cementless implants were used in all patients (Table 2).DVT formation was observed until POD 21 in 95 patients (27.2%). No thrombus was observed in 253 patients (72.8%). The DVT-positive ratio was 9.4% (6/64) in men and 31.3% (89/284) in women. There was a significant difference between the groups (p = 0.0002). The mean age in the DVT-positive group was 73.0 ± 7.9 years (range, 55-84 years), while that in the DVT-negative group was 63.3 ± 11.2 years (range, 39-90 years). Patients in the DVT-positive group were significantly older than those in the DVT-negative group (p = 0.0041).We did not observe any patients with symptom-atic PE. The mean BMI in the DVT-positive group was 22.4 ± 2.2 kg/m2 (range, 18.0-26.2 kg/m2), while that in the DVT-negative group was 22.9 ± 2.9 kg/m2 (range, 17.6-24.9 kg/m2), with no signifi-cant difference (p = 0.2956). The mean operating time was 135.1 ± 41.0 min (range, 93-154 min) in the DVT-positive group and 125.9 ± 20.03 min (range, 104-171 min) in the DVT-negative group, with no significant difference (p = 0.4509). In our hospital, all patients were administered enoxaparin at 2,000 units twice a day for two weeks after surgery and an intermittent pneumatic compres-sion device during the perioperative period for No. of patientsAge(years)BMI (%)Diagnosis　Osteoarthritis　Osteonecrosis　OthersType of operation　Primary　Revision　Operation time(min)Type of anesthesia　General　SpinalBMI, body mass index Table 2　Demographic and surgical characteristics of the patientsMaleFemale284(81.6%)67.5±10.4(48-90)22.3±4.2(17.6-24.7)52120278606402840129.9(93-158)6402840thromboprophylaxis. The thrombus was diagnosed as the distal type in 89 patients (93.7% of the DVT-positive group). Thrombus occurred in the soleal vein in 71 patients (74.7% of the DVT-posi-tive group), but there was no significant difference between the operated and non-operated sides. The thrombus in the popliteal vein (proximal type) was observed in 6 patients (6.3% of the DVT-positive group) (Table 3).Postoperative changes in D-dimer values are shown in Figure 1. At POD 3 and 7, the D-dimer value was significantly higher in the DVT-positive group compared with the DVT-negative group (POD 3: 6.08 µg/ml in the positive group vs. 4.39 µg/ml in the negative group, p = 0.0014; POD 7: 10.65 µg/ml in the positive group vs. 8.79 µg/ml in the negative group, p = 0.021).The postoperative changes in FDP values are shown in Figure 2. There was no significant differ-ence in the FDP values between the DVT-positive and negative groups.The changes in DVT-positive rates are shown in Figure 3. The DVT-positive rates were 3.0% preop-eratively, 9.0% on POD 0, 20.0% on POD 1, 18.1% on POD 3, 18.1% on POD 7, 16.3% on POD 14, and 16.3% on POD 21.Figure 4 shows the time points at which DVT was first observed. In the DVT-positive group, the frequencies for the first observation of DVT were Over-all34866.0±11.222.8±2.75330(94.8%)18(5.2%)3480130.1±34.93480049364(18.4%)53.5±10.4(39-73)25.7±2.1(21.8-32.8)132(115-153)