Information of Clinical Data
In this retrospective study, a total of 1808 inpatients underwent knee arthroplasty were retrospectively enrolled in this study, with 80.75% cases undergoing TKA surgery, and 19.25% cases undergoing UKA surgery. There are 1421 females and 387 males. The number of females in DVT group is markedly higher than that in non-DVT group (P=0.002). Age in DVT group was significantly older than that in non-DVT group (71.67±6.75 vs. 68.22±7.65, P<0.001). There is no significant difference in BMI between DVT group and non-DVT group (26.55±3.79 vs. 27.05±3.85, P=0.21). The binary logistic regression showed that gender-female and age were independent risk factors for preoperative DVT (P=0.002, OR=2.877, 95%CI=1.473- 5.618; P<0.001, OR=1,071, 95%CI=1.041-1.103). (Table 1).
Incidence and Distribution of Preoperative DVT
100 patients (5.53%) were diagnosed as DVT before knee arthroplasty. Among them, 12 cases were found thrombosis in bilateral legs; 48 cases had thrombosis in the affected leg (operated leg), and 40 cases in the contralateral leg. For patients with proximal thrombosis, 1 case occurred in iliac vein, 2 cases occurred in femoral vein, 2 cases occurred in popliteal vein and 1 case had mixed thrombosis in both popliteal and muscular veins. While, for patients with distal thrombosis, majority of cases (n=93) occurred in muscular veins, and 1 case occurred in both muscular and peroneal veins (Table 2).
Comparison of Cumulative Score and Risk Factors between Non-DVT and DVT Groups
The range of cumulative score of the study population is from 0 to 9. Distribution by each cumulative score was 0 (0.11%), 1 (3.98%), 2 (23.95%), 3 (49.72%), 4 (17.26%), 5 (2.93%), 6 (1.33%), 7 (0.50%), 8 (0%) and 9 (0.22%) respectively. The detailed distribution of cases and incidence rate of preoperative DVT is illustrated in Figure 1. The growth of preoperative DVT appears to accelerate according to their cumulative risk score, especially significant for cumulative risk scores of 6-9. Meanwhile, the mean of cumulative score in DVT group is mildly higher than non-DVT group (3.28±1.33 vs. 2.96±0.96, P=0.022) (Table 2).
Among 37 risk factors listed in the Caprini risk assessment mode, age (P=0.012), swollen legs (P=0.035) and history of blood clots (P<0.001) were associated significantly with increased risk of DVT incidence before knee arthroplasty. Gender-female was also significantly correlated with the incidence of preoperative DVT. In addition, DVT incidence before knee arthroplasty in 4 different age groups was analyzed as manifested in Table 3. The incidence rate increased with age significantly (0.00% in ≤40years, 2.43% in 41-60years, 5.26% in 61-74 years and 8.31% in ≥75 years, P=0.012).
Comparison of Risk Levels between Non-DVT and DVT Groups
The distribution by risk levels for these 1808 cases was low (4.09%), moderate (23.95%), high (66.98%) and highest (4.98%). Figure 2 demonstrated the distribution of preoperative DVT in different risk levels. The incidence of preoperative DVT was correlated with increase of risk level. In the highest risk level, 12.22% cases acquired DVT; patients with high and moderate risk level, 5.45%; and patients with low risk, 0%. The difference among 4 risk levels was statistically significant (P=0.07) (Table 4). Additionally, in the low risk group, the preoperative DVT rate were significant lower than other groups (P=0.034), while that in the highest risk group were significant higher than others (P=0,004).
The binary logistic regression in Table 5 showed that compared to low and moderate risk levels, cases in high risk level had mildly higher risk (1.213 times) of preoperative DVT (p=0.436, OR-1.213, 95%CI=0.746-1.973). While, cases in highest had a significantly higher risk (2.93 times) acquiring DVT before knee arthroplasty (P=0.005, OR=2.93, 95%CI=1.375-6.246).