Redefining Injury Severity in Youth Sports: Functional Inability to Walk as a Primary Severity Phenotype (n = 4,829)

ObjectivesDeterminants of functional injury severity in young athletes remain incompletely understood. Conventional assumptions emphasize contact sport participation and skeletal immaturity as major drivers of severe injury; however, severity definitions based on surgery or time loss are strongly influenced by health-care systems and competition contexts. We investigated factors associated with early functional severity after lower-extremity sports injury using a large clinical cohort. MethodsThis cross-sectional observational study analyzed 4,829 lower-extremity sports injury cases in athletes aged [&le;]22 years who presented to a specialized sports injury clinic between January 2017 and November 2025. Severe injury was defined as inability to walk independently at the initial visit. Multivariable logistic regression analysis was performed to evaluate associations between severe injury and age, sex, sport type, injury mechanism, injury location, and physeal status. ResultsSevere injury was most strongly associated with acute injury compared with overuse injury (odds ratio [OR], 31.1; 95% confidence interval [CI], 17.7-54.6; p <.001). Injuries involving the knee and ankle were also significantly associated with severe injury (OR, 2.73; 95% CI, 2.04-3.64; p <.001). Female sex showed a modest independent association (OR, 1.40; 95% CI, 1.06-1.84; p =.017), whereas participation in contact sports, physeal status, and age were not independently associated. ConclusionEarly functional severity after lower-extremity sports injury in young athletes was primarily associated with injury acuity and anatomical involvement of the knee and ankle rather than with sport type or skeletal maturity. These findings challenge conventional exposure-based assumptions and support function-oriented phenotyping for injury surveillance and targeted prevention strategies.