Incidence of lower extremity Injuries in the nfl on turf versus grass
introduction
Football fans and medical providers have likely noticed increased debate regarding injuries and playing surfaces. A recent study was published and supported by the NFL claiming that the injury rate for non-contact knee, foot and ankle injuries has been the same on both turf and grass.
This was met with many players and the NFLPA releasing statements disagreeing with the data. The NFLPA and many players previously released statements recently calling for all artificial turf fields to be replaced with natural grass. Many players released social media statements over the past few weeks.
Image 1: Recent headlines and news stories covering the grass versus artificial turf debate.
The NFL and NFLPA use a third-party company, IQVIA, to compile and analyze data on every injury suffered during every season. Injury reporting is mandated across all 30 NFL teams within an electronic health record system in a robust and consistent manner, thereby eliminating the potential selection bias and variability inherent in similar studies. Injuries and the circumstances surrounding them (contact, impact, activity) are reported with necessary resolution to isolate injury type and mechanism in a structured manner during the course of clinical care by trained medical staff [1-2].
The decision to install synthetic turf is driven by its multiuse capabilities, ease of upkeep, and controllability of playing conditions regardless of most weather conditions. The potential for increased injury risk must be balanced against these desirable aspects of synthetic versus natural turf surfaces [3].
Biomechanical testing of various football cleats on a variety of athletic surfaces has clearly shown differences between natural and synthetic turf in terms of the ability to create a divot, thereby releasing the cleat at loading magnitudes and rates generated during elite athletic competition [4-5]. Synthetic surfaces lack the ability to release a cleat in a potentially injurious overload situation and therefore can generate much greater shear force and torque on the foot and throughout the lower extremity.
One recent study in 2019 by Mack et. al concluded that lower extremity injuries had a higher incidence on artificial turf when compared to natural grass [6]. A total of 4801 lower extremity injuries occurred over five seasons, affecting 2032 NFL players. Over the course of the study, there were 2268 injuries on synthetic turf and 2533 on natural turf, with injury rates per game of 4.1 and 3.5, respectively. The study showed that playing on synthetic turf resulted in a 16% increase in injuries as compared with play on natural turf across all lower extremity injuries resulting in any missed football participation.
Image 2. Table showing data from 2012-2016 of lower extremity injury rates on grass versus artifical turf. Adopted from [6].
An additional study by Loughran et al. analyzed 2460 knee injuries that occurred over 10 NCAA seasons. They concluded that artificial turf is an important risk factor for specific knee ligament injuries. Injury rates for PCL tears were significantly increased during competitions played on artificial turf as compared with natural grass according to their data. Lower NCAA divisions (II and III) were shown to have higher rates of ACL injuries during competitions on artificial turf versus natural grass [7].
The newest study has not been released to the public, but there are tables that have been released representing the data. A meeting occurred between owners that shared this data from the NFL. One showed the adjusted injury rates on the two surfaces from 2018-2021 (Fig.1). Another shows missed injury time per 100 plays.
Image 3: Preliminary data from 2018-2021 showing adjusted injury rates on synthetic versus natural surfaces
Many have viewed the tables and the NFLPA then released a statement calling for a ban of slit-fim surfaces. There are currently six of these surfaces in the NFL : Giants/Jets, Colts, Saints, Bengals, Lions and Vikings. There was then another statement released claiming that the injuries were statistically higher on this surface, but most of them were inversion ankle sprains and that the risk of ACL injury was statistically lower on these surfaces.
Image 4. Preliminary data presented showing higher overall incidence on slit film surfaces.
Summary
In summary, more historical data has shown an increase in non-contact lower extremity injuries on artificial turf when compared to natural grass. Newer data has brought opposing data compared to the last twenty years of research on this and has sparked debate among players and NFL owners. As medical providers, we will have to continue monitoring the updates with this data when it is available to stay up to date.
References
- Mack CD, Franke K, McCarron O, et al. NFL injury surveillance and analytics: improving data collection through use of electronic health records (EHR) [abstract]. Pharmacoepidemiol Drug Saf. 2015;24(suppl 1): 523.
- Matava MJ, Gortz S. The university of the National Football League: how technology, injury surveillance, and health care have improved the safety of America’s game. J Knee Surg. 2016;29(5):370-378.
- Stiles VH, James IT, Dixon SJ, Guisasola IN. Natural turf surfaces: the case for continued research. Sports Med. 2009;39(1):65-84.
- Kent R, Forman JL, Lessley D, Crandall J. The mechanical interactions between an American football cleat and playing surfaces insitu at loads and rates generated by elite athletes: a comparison of playing surfaces. Sports Biomech. 2015;14(1):1-17.
- Kent R, Forman JL, Lessley D, Crandall J. The mechanics of American football cleats on natural grass and infill-type artificial playing surfaces with loads relevant to elite athletes. Sports Biomech. 2015;14(2):246-257
- Mack, Christina D., et al. “Higher rates of lower extremity injury on synthetic turf compared with natural turf among National Football League athletes: epidemiologic confirmation of a biomechanical hypothesis.” The American journal of sports medicine 47.1 (2019): 189-196.
- Loughran, Galvin J et al. “Incidence of Knee Injuries on Artificial Turf Versus Natural Grass in National Collegiate Athletic Association American Football: 2004-2005 Through 2013-2014 Seasons.” The American Journal of Sports Medicine 47 (2019): 1294 – 1301.
