Factors associated with current KOOS-defined knee status among recreational runners: a cross-sectional study

To examine factors associated with current Knee Injury and Osteoarthritis Outcome Score (KOOS)-defined knee status among recreational runners and to develop a nomogram for estimating the probability of this current outcome. In total, 423 recreational runners from Changsha were recruited between June 2023 and March 2024. Demographic and running-related information was collected using questionnaires, and current knee status was defined based on the KOOS. Univariable and multivariable logistic regression analyses were performed to examine factors associated with current KOOS-defined knee status. Five factors showing at least one statistically significant category contrast in the fully adjusted model were jointly refitted in a separate multivariable logistic regression model to construct a nomogram. Model discrimination, calibration, and decision-curve (DCA) performance were evaluated, with internal validation performed using 1,000 bootstrap resamples. Among the 423 recreational runners, 182 (43.02%) met the study definition of current KOOS-defined knee status. In the fully adjusted association model, weekly running frequency, pre-running warm-up, full-marathon participation, previous knee or ankle discomfort, and an annual running volume of 600–900 km were associated with the current outcome. In the jointly refitted five-predictor model, previous knee or ankle discomfort showed the strongest association with the outcome, whereas pre-running warm-up was no longer statistically significant. The apparent AUC, equivalent to the apparent C-index for this binary outcome, was 0.761 (95% CI: 0.716–0.807). After 1,000 bootstrap resamples, the optimism-corrected C-index was 0.737. Bootstrap calibration showed generally reasonable agreement between model-estimated and observed probabilities, and decision-curve analysis in the development sample suggested potential net benefit across a broad range of examined threshold probabilities. Several running-related and health-related characteristics were associated with current KOOS-defined knee status. The internally validated nomogram provides a preliminary visual method for estimating the probability of this status within the study population. Prospective evaluation and external validation are required before the model can be used to predict future injury or support routine clinical decision-making. Registration number: ChiCTR2200064956. Date of registration: 24 October 2022.