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  • Chi square tests with significance set to

    2022-07-02

    Chi-square tests with significance set to p<0.05 were used to compare the comorbidities and complication rates between the cohorts at each time point. When Chi-square testing demonstrated a significant difference in the three-way comparison between anticoagulation cohorts, adjusted residuals (AR) were calculated to measure the contributions of individual cells, with values ≥2 or ≤−2 considered statistically significant [16].
    Results There were 4090 hip fracture patients included in the study. 2326 of these received enoxaparin, 929 received XaI, and 835 received warfarin. The mean CCI for each group was 3 (Table 2). There were some significant differences in demographics between the three cohorts (Table 2). There was a significant difference in DVT rates between the three groups at thirty days (5.03% warfarin, 2.91% XaI, and 3.48% enoxaparin, p=0.047. Higher rates of DVT in the warfarin group contributed significantly to this difference (AR=2.35 warfarin). AR in the XaI and enoxaparin DOI hydrochloride were non-significant, but less than zero, indicating fewer observed DVTs than statistically expected (−1.41 XaI, −0.72 enoxaparin) (Fig. 1). There were no significant differences in DVT rates at 2 weeks, 6 weeks, or ninety days (Fig. 1). For PE, there were significant differences between the groups at all time points studied following Chi-square analysis (2 weeks: 1.80% warfarin, 1.72% XaI, 0.60% enoxaparin, p=0.002; thirty days: 2.04% warfarin, 1.83% XaI, 0.95% enoxaparin, p=0.026; 6 weeks: 2.04% warfarin, 1.83% XaI, 0.99% enoxaparin, p=0.037; ninety days: 2.63% warfarin, 2.15% XaI, 1.25% enoxaparin, p=0.017)(Fig. 2). At 2 weeks, adjusted residuals were significant for all cells: the warfarin and XaI groups had significantly more PE events than expected (2.16 warfarin, 2.07 XaI), while the enoxaparin group had significantly fewer (−3.51 enoxaparin). At the thirty day and six week time points, only lower rates than expected in the enoxaparin groups were found significant after calculation of adjusted residuals (thirty days: 1.86 warfarin, 1.37 XaI, −2.68 enoxaparin; 6 weeks: 1.77 warfarin, 1.29 XaI, −2.54 enoxaparin). At ninety days, there were significantly more events in the warfarin group than expected and significantly fewer in the enoxaparin group (AR=2.23 warfarin, 1.11 XaI, −2.75 enoxaparin)(Fig. 2).
    Discussion There are relatively few high quality therapeutic studies assessing the effect of chemoprophylaxis on VTE rates among hip fracture patients, and even fewer data available which compare the efficacy of different agents. One of the studies with the highest methodologic quality on the topic is a multicenter, multinational, randomized controlled trial by Rodgers et al. from 2000, in which 13,356 hip fracture patients were randomized to either an antiplatelet or placebo, and complications were tracked for 35days [3]. The authors found that the rates of DVT and PE at 35days were 1.0% (compared to 1.5% in the placebo group) and 0.7% (compared to 1.2%), respectively, and concluded that chemoprophylaxis was effective for VTE risk reduction [3]. In the current study, each of the patient cohorts received some form of chemoprophylaxis, but we found 30day DVT rates between 2.91–5.03% and PE rates between 0.95–2.04%, which are slightly higher than the Rodgers et al. data [3]. The reasons for this are unknown, and likely multifactorial. There is little information in the Rodgers study regarding the baseline medical comorbidities and general health status of the patients [3], and it is possible our American patient population had poorer overall health status at the time of surgery, which may have increased their risk for VTE. Additionally, up to 44% of patients in the previous study received both the randomized treatment of an antiplatelet in addition to unfractionated heparin or enoxaparin [3]; it is possible this use of dual chemoprophylaxis reduced VTE rates in that study relative to our cohort.