Early Ambulation Reduces the Risk of Venous Thromboembolism after Total Knee Replacement

Purpose:
Symptomatic venous thromboembolism (VTE) is a frequent complication following total knee replacement (TKR). This study was performed to analyze the association between acute VTE and potential risk factors, including delivery of pharmacologic prophylaxis, degree of obesity and duration of immobility.

Background/Significance:
Although widely recognized as a potentially preventable complication, acute VTE is diagnosed after TKR in 2.0 to 2.5% of all cases. VTE leads to increased length-of-stay and higher costs, and may lead to complications such as fatal pulmonary embolism, post-thrombotic syndrome, and anticoagulant-related bleeding. We conducted a case control study to determine the effect of patient factors (age, gender, BMI) and guideline-based interventions on the risk of acute VTE after TKR.

Methods:
130 cases diagnosed with acute VTE within 90 days of TKR between 2008-2010 were identified at 15 academic medical centers; ~4 controls without acute VTE were randomly selected at each site (N=463). Data obtained by standardized chart abstraction included age, gender, BMI, type of TKA (unilateral vs. simultaneous bilateral), use of pharmacologic and mechanical prophylaxis, and timing of initiation of post-op ambulation. Multivariable logistic regression was used to analyze the strength of the association of these risk factors with post-operative acute VTE.

Results:
Factors associated with development of VTE included undergoing simultaneous-bilateral TKR vs. unilateral (OR=3.3, 95% CI:1.4-7.5, P=<.01); receipt of recommended pharmacologic prophylaxis vs. mechanical (OR=0.5, 95% CI:0.2-1.09, P=.07); and ambulation on post-operative day 1 or 2 vs. day 3 or later (OR=0.3, 95% CI:0.1-0.88, P=<.01). BMI≥35 was not significantly associated with VTE. 47% of cases first ambulated on day 3 or later, vs. 37% of controls; 61% of all patients ambulated within 24 hours following surgery.

Conclusions and Implications for Practice:
Ambulation within 48 hours was associated with a 70% reduction in the risk of VTE. Although prophylaxis is typically the focus of VTE prevention strategies, this finding demonstrates that early ambulation, a nursing and physical therapy function, directly affects this important health care outcome.