Efficacy and limitations of a web-based native adult knee septic arthritis calculator in urban trauma care

Background: Septic arthritis of the knee presents significant diagnostic challenges. Traditional diagnostic methods demonstrate limited sensitivity and specificity, whereas delayed intervention risks irreversible joint damage. A web-based septic arthritis calculator offers quantifiable risk assessment, but its performance requires validation. Questions/Purposes: We evaluated (1) diagnostic accuracy of a web-based septic arthritis calculator in a tertiary referral center and (2) optimal risk thresholds for recommending surgical intervention and for confidently excluding septic arthritis. Methods: We retrospectively analyzed 121 consults for suspected septic arthritis of the knee including arthrocentesis in adult patients at a tertiary referral center from 2018 to 2023. Newman criteria served as the diagnostic gold standard for septic arthritis. We calculated risk probabilities using the web-based tool incorporating 6 clinical and laboratory variables. Receiver operating characteristic analysis identified optimal thresholds for surgical intervention and assessed diagnostic performance. Results: The calculator demonstrated excellent discrimination between septic (n = 75) and nonseptic (n = 46) joints (area under the curve of 0.97 [95% confidence interval 0.95–0.99; P < .001). Median calculated probabilities for sepsis were 80% vs 4% for nonseptic cases. Optimal thresholds included 58% for recommending surgical intervention (sensitivity 89%, specificity 98%, positive predictive value 99%) and 24.6% for excluding septic arthritis (sensitivity 96%, specificity 87%, negative predictive value 93%). Both thresholds achieved 93% correct classification. Conclusions: The web-based calculator provides excellent diagnostic accuracy and clinically relevant thresholds derived from ROC analysis: ≥58% for recommending surgical intervention and <24.6% for confidently excluding septic arthritis. These findings support systematic implementation in tertiary referral centers to enhance diagnostic precision and optimize resource allocation, although prospective validation remains essential. Level of Evidence: III.