Evaluation of VTE Risks Associated with a Risk Stratification Protocol for Venous Thromboembolism Prophylaxis in Post-op Arthroplasty Patients


Background: VTE is a common complication following orthopedic surgery. Current guidelines have yet to identify definitive recommendations for which medications would best prevent VTE, but they recommend using patient-specific factors to guide prophylaxis choices. Risk stratification protocols are becoming increasingly popular to incorporate patient factors into therapy choice.

Objectives: To identify the efficacy of a risk stratification protocol used to determine VTE prophylaxis following primary TKA or THA.

Study Design: Retrospective cohort study

Patients/Methods: Adult patients who underwent primary TKA or THA at the University of Utah Hospital in 2013 or 2017 were included. Patients from 2017 received warfarin or aspirin based on the risk stratification protocol while patients from 2013 received empiric warfarin. The 2013 patients were stratified based on the protocol during chart review. VTE rates in the high-risk and low-risk patients from before the protocol initiation were compared to the rates in respective groups after the initiation.

Results: 1,390 TKA/THA procedures were included in the study. 26 of these patients experienced a VTE event. VTE rates in both low-risk TKA and THA procedures resulted in nonsignificant P-values of 0.869 and 0.671. High-risk TKA procedures also showed a nonsignificant difference in VTE rates (0.131).

Conclusion: This risk stratification protocol resulted in similar VTE event rates across all cohorts. This indicates that the protocol does not result in excess VTE risk and may prevent over-anticoagulation. Another arm of this study is looking at bleeding rates in this population.

Published in College of Pharmacy, Virtual Poster Session Spring 2020


  1. Kelsey, Nicely presented. While I see that the risk stratification decision making does not lead to different outcomes now relative to 2013, I am curious about the greater number of VTE events overall in the low-risk patients in 2017 cohort. Is this acceptable because they’re at low risk of adverse outcomes of a VTE event, so we err on having those to avoid a bleeding event?

    1. The event rate for low-risk patients in 2017 does appear to be higher due to the increased number of events; however, one piece of information that is not apparent in the poster is the number of procedures that were evaluated in each group. The low-risk groups in 2017 had a larger number of procedures than the groups in 2013. Low-risk TKAs in 2017 had 476 procedures with only 211 procedures in 2013. THAs had 305 and 174 procedures, respectively.

      Your comment about the higher number of VTE events being acceptable due to the lower risk of adverse events is on the right track. Overall, we want to balance the risk of a VTE and the risk of a bleeding event because these can both have serious effects on lifestyle and healing following the procedure. Cassidy’s poster looks at the rate of bleeding events in this same population so that we can evaluate both the efficacy and the safety of the protocol.

  2. Nice work, Kelsey. I’m wondering about the difference in number of total VTE in the high risk TKA group (7 vs. 1)…the p-value for the comparison was not significant but I wonder if there could potentially be a power problem given the small number of events. It might have been helpful to report the % of patients with VTE events in the bar graph so as to take into account any differences in the number of patients in each group. Were the hazard ratios reported? I didn’t see them.

    1. I agree that due to the small number of events there is likely a problem in regards to power, particularly with this group. The high-risk group in 2013 only had 92 patients and the low-risk group had 66 patients. 7.6% of TKA procedures in 2013 resulted in a VTE while 1.5% of procedures in 2017 results in an event. With both the small number of patients and the small number of events, this data is likely not sufficiently powered. Unfortunately, I neglected to include the hazards ratios within the poster. For High-risk TKAs the hazard ratio was 0.199 with a 95% CI of 0.024 to 1.617.

      Of note, the high-risk groups, across both years, were treated with warfarin. There is a chance that these results may be confounded by other variables such as improvement in surgical techniques or warfarin/INR management which was not assessed in this study.

  3. Kelsey, Interesting study. So many decisions in health care come down to evaluation of risk. good work.

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