High Altitude is an Independent Risk Factor for Postoperative Venous Thromboembolism Following Primary Total Knee Arthroplasty: A Large Database Study

Introduction: Venous thromboembolism (VTE) is a relatively uncommon but potentially fatal complication following total knee arthroplasty (TKA). High altitude may induce physiological changes that can predispose patients to VTE. The purpose of this study was to determine if high altitude is an independent risk factor for postoperative VTE following TKA.

Methods: A large claims database was queried for patients who underwent TKA at high elevation (≥ 4,000 feet) and low elevation (≤ 100 feet) using Current Procedural Terminology (CPT) codes, International Classification of Disease (ICD) codes, and zip codes. High- and low-altitude cohorts were matched 1:3 by 5-year age range, sex, Charlson comorbidity index (CCI), and comorbidities including diabetes mellitus, obesity (BMI [body mass index] ≥ 30), hypertension, and tobacco use. There were 57,135 patients included in the high-altitude group and 171,322 in the low-altitude group. Outcome measures included 30- and 90-day incidence of VTE, deep venous thrombosis (DVT), and pulmonary embolism (PE). Chi-square tests were used to determine differences in demographics between cohorts. Binomial logistic regression analysis was used to determine postoperative rates of VTE, DVT, and PE.

Results: The incidence of VTE was significantly higher for the high-altitude group than the low-altitude group at 30 days (OR [odds ratio] 1.15 [95% CI (confidence interval) 1.02 to 1.30], P = 0.022) and 90 days follow-up (OR 1.20 [95% CI 1.08 to 1.34], P = 0.0007). The incidence of DVT was significantly higher for the high-altitude cohort at both 30- (OR 1.30 [95% CI 1.10 to 1.54], P = 0.002) and 90-days postoperatively (OR 1.36 [95% CI 1.18 to 1.57], P < 0.0001). The incidence of PE within 30 and 90 days was not significantly different between groups.

Conclusions: High altitude (> 4,000 feet) is an independent risk factor for VTE following TKA. Patients who undergo TKA at surgical centers greater than 4,000 feet in elevation are more likely to develop VTE and DVT within 30- and 90 days postoperatively. Surgeons may account for high altitude as a risk factor and determine the most suitable postoperative prophylaxis method for their patients.