Patients with obesity have a higher risk of periprosthetic joint infection and more frequent polymicrobial infections after knee arthroplasty: A nationwide register‐based study from Denmark

PURPOSE: To compare the 2-year incidence of (1) revision due to periprosthetic joint infection (PJI) and (2) all-cause revision after primary knee arthroplasty (KA) in patients with/without obesity and to compare the microbial profiles in early (≤ 90 days) and late (91-730 days) PJI. METHODS: . Cox proportional hazards models estimated hazard ratios (HRs) with corresponding two-sided 95% confidence intervals (95% CIs) for PJI and all-cause revision within 2 years. Analyses included crude and propensity score-adjusted models based on health and socioeconomic data. Microbial profiles were compared using absolute risk difference (ARD) with 95% CIs in the early and late post-operative periods. RESULTS: Among 111,117 eligible patients, 41,306 had obesity (mean BMI: 34.6) and 59,993 did not (mean BMI: 26.1). Patients with obesity were slightly younger and had higher use of glucose-lowering medication. Patients with obesity had a higher risk of PJI revision than those without obesity (482 [1.2%] vs. 559 [0.9%]; crude HR: 1.25 [1.11-1.42], and propensity-adjusted HR: 1.30, 95% CI: 1.14-1.48). The adjusted risk of all-cause revision was comparable (1494 [3.6%] vs. 1893 [3.2%]; HR: 1.05, 95% CI: 0.98-1.13). Within 90 days, patients with obesity had more polymicrobial infections (62 [18.5%] vs. 43 [11.3%]; ARD: 7.2%, 95% CI: 2.0%-12.5%) and more non-staphylococcal gram-positive organisms (69 [21%] vs. 54 [14%]; ARD: 6.3%, 95% CI: 0.8%-12%). Staphylococcus aureus was the most frequent pathogen in both groups (127 [38%] vs. 136 [36%]; ARD: 2.0%, 95% CI: -5.1% to 9.1%). CONCLUSIONS: Obesity was associated with an increased 2-year risk of PJI after KA; however, the risk of all-cause revision was comparable to that in patients without obesity. Within 90 days, patients with obesity exhibited a higher incidence of polymicrobial infections and non-staphylococcal gram-positive organisms. LEVEL OF EVIDENCE: Level II, prognostic studies-investigating natural history and evaluating the effect of a patient characteristic.