Increased risk of infection and reoperation following total knee arthroplasty in patients under 40

BACKGROUND: Total knee arthroplasty (TKA) is increasingly performed in younger patient populations. This study aimed to compare perioperative outcomes between patients under 40 and those over 65, stratified by surgical indication. METHODS: This retrospective study used the Epic Cosmos dataset to identify primary TKA patients under 40 years old (n = 3,177) or over 65 (n = 698,662). Patients were stratified by surgical indication (primary osteoarthritis, post-traumatic osteoarthritis, rheumatoid arthritis, avascular necrosis, and multiple indications) using ICD-10 codes. Outcomes included superficial wound dehiscence, infection, readmission, and ipsilateral reoperation, assessed at 90 days and 1 year postoperatively. Differences between age groups were assessed using adjusted odds ratios (95% confidence intervals) derived from multivariable logistic regression models adjusted for sex, body mass index, comorbidity burden, insurance status and smoking status with significance set at p < 0.05. A sensitivity analysis in the overall cohort tested the interaction between age group and surgical indication. RESULTS: Surgical indications differed significantly between cohorts (standardized proportions difference 0.939, p < 0.001), with osteoarthritis accounting for 97.8% of cases in patients >65 compared to 64.6% in patients <40. Younger patients had higher rates of post-traumatic osteoarthritis (2.4% vs 0.1%) and multiple diagnoses (20.7% vs 1.6%). Among patients with osteoarthritis, those under 40 had significantly higher 90-day odds of infection (OR 3.16, 95% CI 2.29-4.35), superficial wound dehiscence (OR 1.91, 95% CI 1.34-2.72) and ipsilateral reoperation (OR 3.91, 95% CI 3.34-4.58), which persisted at 1 year (infection OR 2.79, 95% CI 2.13-3.67; superficial wound dehiscence OR 1.91, 95% CI 1.41-2.59; reoperation OR 3.44, 95% CI 3.00-3.94). Patients under 40 with multiple diagnoses had elevated odds of infection at 90 days (OR 2.06, 95% CI 1.15-3.69) and 1 year (OR 1.80, 95% CI 1.09-2.95), and ipsilateral reoperation at 90 days (OR 3.10, 95% CI 2.25-4.25) and 1 year (OR 2.71, 95% CI 2.06-3.55). In the overall cohort, the effect of age differed significantly by surgical indication for all outcomes except superficial wound dehiscence. CONCLUSION: Patients under 40 undergoing Total Knee Arthroplasty are at increased risk for prosthetic joint infection, superficial wound problems and ipsilateral reoperation at 90 days and 1 year when compared to those over the age of 65, independent of smoking status and comorbidity burden. Those with multiple indications for surgery are also at increased risk for infection and same-side reoperation at both time points.