Does playing surface affect the risk of anterior cruciate ligament injuries in the National Football League? A look at the 2017 - 2021 NFL seasons.

Background: Anterior cruciate ligament (ACL) injuries are devastating injuries for athletes. Prior studies have shown increased ACL injury rates on non-natural surfaces versus natural grass in several sports. The purpose of this study is to calculate the prevalence of ACL injuries in the NFL on natural versus non-natural surfaces to determine if there is a significant increase on non-natural surfaces.

Methods: Accessing publicly available data for NFL seasons beginning with the 2017-2018 season through 2021-2022 seasons, all ACL injuries with publicly available data concerning timing and playing surface were recorded and categorized according to playing surface. Practice injuries or those without an identifiable playing surface were excluded. Incidence rates, defined as ACL ruptures per game, were calculated. ACL injuries were recorded for each playing surface, as well as the combined category of non-natural grass surface. Odds ratio was calculated to compare the risk of ACL rupture on non-natural surfaces vs natural grass.

Results: During the 2017-2021 NFL seasons, 173 ACL ruptures were identified with known surfaces. Injury rate for non-natural surfaces was 0.134 compared to 0.097 for grass. Injury rate ratio for non-natural vs natural grass surfaces was 1.211, a 21.1% increased risk of ACL injury in the NFL on non-natural surfaces vs natural grass. OR for non-natural surfaces 1.239 (95% CI 0.900-1.704). Based on these findings there is a trend toward increased risk of ACL injury on non natural grass surfaces, however this did not reach statistical significance.

Conclusion: Numerous published studies show trends toward increasing rates of ACL injuries on non-natural playing surfaces vs natural grass. Based on our findings the difference is not statistically significant, however it does trend toward increased risk of ACL injury with non-natural surfaces. Further studies should be performed with larger sample sizes in order to further determine the risk of non-natural surfaces.