(18) Lower Extremity Strains in the U.S. National Football League, 2015-2019

Publication Number: 692

Background: Lower extremity (LEX) strains, including hamstring, quadriceps, adductor, and calf strains, are among the most common injuries in sports. Injury reduction strategies and policies can be refined by understanding occurrence and incidence using Electronic Medical Record (EMR) data linked to player participation exposure information.

Objectives: To describe the incidence of LEX strains in professional American football using a standardized, linked EMR database.

Methods: We conducted a retrospective, observational cohort study of LEX strains in the National Football League (NFL) during the 2015-2019 seasons identified in the standardized League-wide EMR (n=32 teams). Injury data in the EMR were linked with game statistics and player participation to calculate injury risk and incidence rates. All players who played in at least one NFL game or who sustained a LEX strain during NFL participation (game or non-game) were included in risk calculations. LEX Strain frequency was calculated by setting (game, practice, conditioning), season (offseason, preseason, regular season, postseason), and roster position. Game incidence rates per 1,000 plays and 95% confidence intervals (CI) were calculated for season, roster position, and play type.

Results: Across 5 seasons, 5,780 LEX strains were reported among 2,769 players (1-season risk: 26.7%, 95% CI 26.0%-27.3%), 69% (n=4,015) of which resulted in time-loss. Among time-loss strains, 58.5% were hamstring (n=2,347), 21.3% were adductor (n=855), 11.8% were calf (n=474), 8.0% were quadriceps (n=323), and 0.4% affected multiple muscle groups (n=16). Most were reported during preseason practices (n=1,076; 27%) and regular season games (n=1,060; 26%). Among preseason practice strains, 72% (n=775) were reported during the Training Camp period. In games, punt plays had nearly twice the rate as kickoff plays (14.9/1,000 plays; 95% CI 13.1-17.0 vs. 7.5/1,000 plays; 95% CI 6.2-8.9, respectively) and over three times the rate as pass (4.3/1,000 plays; 95% CI 4.0-4.7) and run (2.6/1,000 plays; 95% CI 2.3-2.9) plays.

Conclusions: LEX strains impact 1 in 4 NFL players each season and occur mostly during preseason practices and regular season games, causing a high patient burden in terms of pain, injury management, and time lost from physical activity. The 2-week period of Training Camp practices comprised 19% of all time-loss strains which draws focus on the need for reduction efforts as players acclimate to sports participation. Future efforts to link wearable devices with enriched medical data are important for injury reduction research. Real-world evidence taken from a linked EMR and exposure-based dataset can provide complete and robust data capture, allowing for targeted reduction efforts.