Preoperative Anemia as a Predictor of Periprosthetic Joint Infection Following Total Knee Arthroplasty: A Continuous Variable Analysis

Background: Preoperative anemia, defined by the World Health Organization as hemoglobin levels below 12.0 g/dL in women and below 13.0 g/dL in men, has been associated with postoperative complications following total knee arthroplasty (TKA). This study sought to utilize preoperative hemoglobin levels to assess the risk of early postoperative adverse events following elective TKA. Methods: An inpatient and outpatient encounters database was utilized to identify all primary TKA patients between 2016 and 2021 who had a preoperative hemoglobin value within 28 days of surgery. Restricted cubic splines were generated utilizing multivariable logistic regression models to assess the relationship between hemoglobin, as a continuous variable, and the 90-day risk of periprosthetic joint infection (PJI), aggregate medical complications, and aggregate surgical complications. Hemoglobin changepoints were identified beyond which the risk of PJI significantly increased. In total, 61,857 TKA patients (women: 37,800 [61.1%]; men: 24,057 [38.9%]) were identified with preoperative hemoglobin values, of which 367 (0.60%) developed a PJI. Results: The risk of PJI, aggregate medical complications, and aggregate surgical complications was found to significantly increase for patients who had a hemoglobin < 13.0 g/dL (men < 13.0 g/dL; women < 12.7 g/dL). Patients who had a hemoglobin of 10 g/dL had a 1.86-fold (95% confidence interval [CI]: 1.44 to 2.41) increased risk of PJI, a 2.72 (CI: 2.56 to 2.90) times increased risk of medical complications, and a 2.16-fold (CI: 1.82 to 2.57) increased risk of aggregate surgical complications. No increased risk of adverse events was found for hemoglobin values > 13.0 g/dL. Conclusions: Preoperative anemia is associated with early postoperative adverse outcomes, including PJI, following elective TKA. Further study is necessary to determine if correction of low preoperative hemoglobin decreases is associated with decreased complication rates or if low hemoglobin values are a surrogate for chronic diseases that increase the postoperative risk of complications.