Tyler J. Humphrey, BA; Todd D. O’Brien, MD, MBA; Christopher M. Melnic, MD; Kimberly I. Verrier, NP; MGB Arthroplasty Outcomes Writing Committee; Hany S. Bedair, MD
Humphrey, Tyler J., et al. “Morbidly Obese Patients Undergoing Primary Total Joint
Arthroplasty May Experience Higher Rates of Venous Thromboembolism When Prescribed
Direct Oral Anticoagulants vs Aspirin.” The Journal of Arthroplasty 37.6 (2022): 1189-1197.
Summary by Nareena Imam, BA
Although the risk of developing venous thromboembolism (VTE) after total joint arthroplasty
(TJA) is 1.8%,1 consequences are life-threatening. Prophylactic anticoagulation is
recommended,2 but no universal regimen currently exists. The International Consensus Meeting
(ICM) found low-dose aspirin to be the optimal agent for VTE prophylaxis after TJA due to its
efficacy and safer risk profile than other anticoagulants.3
Patients with obese BMI (>40 kg/m 2 ) have a higher risk of complications after TJA, including
VTE.4,5 However, much remains unknown regarding the ideal agent to prevent VTE in these
patients. Humphrey et al. investigated the risk of VTE in obese patients when prophylactically
treated with direct-acting oral anticoagulants (DOACs) or aspirin.6 They conducted a
retrospective study of 897 patients undergoing unilateral primary TJA receiving either DOACs,
specifically apixaban or rivaroxaban, or aspirin postoperatively for VTE prophylaxis. A
multivariate logistic regression model was used to assess risk for VTE with prophylactic agent
for patients taking DOACs alone, aspirin alone, or both.
The study found obese patients prescribed DOACs alone after TJA had a higher likelihood of
VTE compared to those taking aspirin alone (OR 2.962, 95% CI 1.224-7.165, p = 0.016). Usage
of DOACs with aspirin carried a higher risk of postoperative VTE compared to aspirin alone
(OR 3.545, 95% CI 1.157-10.864, p = 0.027). TKA patients had a higher likelihood of
postoperative VTE than THA patients (OR 4.830, 95% CI 1.294-18.022, p=0.019). Apixaban
compared to aspirin had an increased risk of developing VTE postoperatively (OR 3.146, 95%
CI 1.029-9.614, p=0.044). Rivaroxaban compared to aspirin did not result in a higher risk for
VTE (OR 2.916, 95% CI 0.933-9.108, p = 0.066).
The authors concluded obese patients undergoing TJA taking DOACs alone or with aspirin have
a higher risk of postoperative VTE compared to aspirin alone. Risk of VTE in obese patients is
higher after TKA than THA. However, this study had significant limitations. Primarily, there
may be overfitting of the multivariate logistic regression model. Although common, performing
a univariate analysis to select variables for inclusion in the multivariate regression model raises
the risk of overfitting.7 Additionally, while statistical significance was defined as a p-value <
0.05, a p-value of <0.20 on univariate analysis was used to determine inclusion of variables in
the model. Further, shrinkage techniques to adjust for model optimism were not discussed in the
study, limiting validity.7 Lastly, aspirin dose, comorbidities, and medication interactions were
- Samama CM, Ravaud P, Parent F, Barre J, Mertl P, Mismetti P. Epidemiology of venous
thromboembolism after lower limb arthroplasty: the FOTO study. J Thromb Haemost
2007;5(12):2360-7. DOI: 10.1111/j.1538-7836.2007.02779.x.
- Mont MA, Jacobs JJ. AAOS clinical practice guideline: preventing venous
thromboembolic disease in patients undergoing elective hip and knee arthroplasty. J Am
Acad Orthop Surg 2011;19(12):777-8. DOI: 10.5435/00124635-201112000-00008.
- The ICMVTEH, Knee D. Recommendations from the ICM-VTE: Hip & Knee. J Bone
Joint Surg Am 2022;104(Suppl 1):180-231. DOI: 10.2106/JBJS.21.01529.
- Werner BC, Evans CL, Carothers JT, Browne JA. Primary Total Knee Arthroplasty in
Super-obese Patients: Dramatically Higher Postoperative Complication Rates Even
Compared to Revision Surgery. J Arthroplasty 2015;30(5):849-53. DOI:
- Zusmanovich M, Kester BS, Schwarzkopf R. Postoperative Complications of Total Joint
Arthroplasty in Obese Patients Stratified by BMI. J Arthroplasty 2018;33(3):856-864.
- Humphrey TJ, O’Brien TD, Melnic CM, Verrier KI, Committee MGBAOW, Bedair HS.
Morbidly Obese Patients Undergoing Primary Total Joint Arthroplasty May Experience
Higher Rates of Venous Thromboembolism When Prescribed Direct Oral Anticoagulants
vs Aspirin. J Arthroplasty 2022;37(6):1189-1197. DOI: 10.1016/j.arth.2022.01.089.
- Babyak MA. What you see may not be what you get: a brief, nontechnical introduction to
overfitting in regression-type models. Psychosomatic medicine 2004;66(3):411-421.