Revisiting the International Normalized Ratio (INR) Threshold for Complications in Primary Total Knee Arthroplasty An Analysis of 21,239 Cases

Background: Consensus guidelines recommend use of the international normalized ratio (INR) to predict the risk of perioperative bleeding in orthopaedic surgery. However, current recommendations for targeting an INR of <1.5 are based on studies across all surgical disciplines. This study examined the impact of the INR on perioperative bleeding, mortality, postoperative infections, length of hospital stay (LOS), and readmissions following primary total knee arthroplasty (TKA). Methods: We retrospectively reviewed the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database for adult patients who underwent primary TKA from 2010 to 2016. Patients for whom an INR had been recorded within 1 day before the surgery were stratified and analyzed for perioperative bleeding, mortality within 30 days, deep wound and superficial infections, LOS, and readmissions. Multivariable regressions were utilized to adjust for differences in demographics and comorbidities among INR groups. Results: Of 21,239 patients, 57.2% had an INR of 1.0; 38.1% had an INR of >1.0 to 1.25, 3.9% had an INR of >1.25 to 1.5, and 0.8% had an INR of >1.5. After adjustment, a progressively increased bleeding risk was found with an INR of >1.0 to 1.25 (odds ratio [OR] = 1.19, 95% confidence interval [CI] = 1.07 to 1.31, p = 0.001), an INR of >1.25 to 1.5 (OR = 1.29, 95% CI = 1.02 to 1.63, p = 0.033), and an INR of >1.5 (OR = 2.02, 95% CI = 1.29 to 3.14, p = 0.002) relative to an INR of Patients with an INR of >1.5 were at increased risk for infection (OR = 5.34, 95% CI = 2.45 to 11.68, p < 0.001), but only patients with an INR of >1.25 to 1.5 were at increased risk for mortality (OR = 3.37, 95% CI = 1.31 to 8.63, p = 0.011) relative to those with an INR of Overall and TKA-related readmission rates and LOS were significantly increased for patients with an INR of >1.25 to 1.5 or an INR of >1.5. Conclusions: An INR of >1.25 to 1.5 was associated with increased bleeding, infection, and mortality rates following TKA, and an INR of >1.5 was associated with increased bleeding and infection rates. Current INR target recommendations in consensus guidelines should be reconsidered.