¹Card R, ²Harrington J, ³Huish E, ³Pettegrew J
¹Valley Consortium for Medical Education, Modesto, CA, USA; ²Vally Consortium for Medical Education, Modesto, CA, USA; ³VCME, Modesto, CA, USA

Introduction
Anterior cruciate ligament (ACL) injuries are common and potentially devastating injuries for high level athletes. Prior studies have shown increased ACL injury rates on non-natural playing surfaces (i.e. artificial turf) vs natural grass in several sports. Previous studies that include National Football League (NFL) players have shown varying results. These studies predate the use of newer field turf playing surfaces. There is also an increasing presence of artificial turf playing surfaces in the NFL, with more teams adopting this type of surface instead of natural grass, which may be leading to an increase in ACL injuries in the NFL. The purpose of our study was to determine if there is an increase in ACL injury risk on non-natural versus grass playing surfaces in the NFL.

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

Results
During the 2017 – 2021 NFL seasons, a total of 173 ACL ruptures were identified with a known playing surface. Incidence rate for non-natural surfaces was found to be .0588 compared to 0.0485 for grass. Odds ratio for non-natural vs natural grass playing surfaces was 1.21 representing a 21% increased risk of ACL injury in the NFL on non-natural playing surfaces vs natural grass (95% confidence interval 0.89-1.65). 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 studies have been published showing trends towards 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 playing surfaces. Further studies should be performed with larger sample sizes in order to further determine the risk of non-natural surfaces. There continues to be an increasing trend in the NFL towards the utilization of artificial turf playing surfaces. While more evidence is necessary to make recommendations regarding NFL playing surfaces, there are trends in recent years towards increased ACL injuries with non-natural vs natural grass playing surfaces.