(339) Risk of lower extremity injury following concussion in the National Football League

Background: Literature on injury risk after concussion is mixed, with varied results based on design, comparison group, and outcome (timing/injury type).

Objectives: To examine whether National Football League (NFL) players had increased risk of lower extremity (LEX) sprain, strain, or fracture after concussion.

Methods: This retrospective study analyzed time to LEX injury among players concussed in 2015-2021 pre- or regular season NFL games compared to a) players participating in the same game, and b) players who sustained a missed time upper extremity injury in the study period using a robust electronic medical records database linked to player participation data. Cox Proportional Hazards models adjusted for prior-year injuries, tenure, and roster position. Additional models accounted for time missed from participation after injury.

Results: Without accounting for time missed from participation after concussion, the hazard of LEX injury was 19% higher among concussed players compared to non-concussed (HR=1.19, 95% CI 0.97-1.44). However, accounting for time missed, the hazard of LEX injury was 11% higher among concussed players compared to non-concussed (HR=1.11, 95% CI: 0.90-1.36). The hazard of LEX injury for concussed players was lower than players with upper extremity injuries (HR=0.78, 95% CI: 0.60-1.02). This ratio did not change when days missed due to injury (concussion or upper extremity) was included as a covariate. Results were largely consistent across follow-up times, with slightly stronger associations in the 30 days immediately following the index event.

Conclusions: While NFL players returning from concussion did have elevated risk of subsequent injury compared to non-concussed players in the same game, they had a lower risk of subsequent LEX injury compared to players returning from upper extremity injury, although neither result was statistically significant. Using an injured comparison group produced different results than an all-player comparison group and controlling for days missed also influenced results, suggesting that observed increased subsequent injury risk may be related to days missed from training and deconditioning rather than neurocognitive effects.