Ask Dr. Geier – Are ACL tears more common on grass or FieldTurf?

The following question is one I received from a long-time listener of my show and someone who frequently comments on the discussions in social media. Since his question involves a topic that requires a complex explanation, I am breaking my answer up into a blog post and a discussion during the In the Zone segment of Episode 74 of The Dr. David Geier Show.

I want to remind you that I answer about four to six readers’ questions on my show each week. So if you have a question, or if you just like hearing me discuss sports injuries, treatments, surgeries, and prevention, please check out The Dr. David Geier Show.

As always, please remember my disclaimer that I cannot and will not offer specific medical advice in this column or elsewhere on the blog, on my show, by email, or in social media. This is meant for general information and education. Please consult with your doctor for specific medical advice.

Hello Dr. Geier,

I’ve enjoyed reading your articles, following you on Facebook/Twitter and listening to your shows on podcast. I really appreciate how you express how important athletic trainers are in the sports world. I work at a local high school with 800+ athletes and have very little support from my AD and coaches. But we just started the program so it is slowly building.

My question for you is do you think playing on turf field compared to regular grass has an impact on injuries?

Our varsity football team practices on grass field and play more than half of their games on turf. We had 3 meniscus injuries on the turf fields. Two were medial and one lateral; all 3 were repair. Also had a tibia/fibula fracture without impact. When asking the injured kids what they thought about the turf they all said it feels like their cleats stick into the ground.

Thank you for your time!

Gino Mangino, ATC, NREMT-B
Assistant Athletic Trainer
Pueblo South High School

Thanks Gino for the question and the thoughts on the show and social media. It means a lot. I actually like your question and think that there is a lot of information worth discussing. It would be too much for one blog post, so I am going to break up my thoughts. Here I want to address knee injuries – and ACL injuries specifically – and their incidence rates on natural grass compared to turf. In my next podcast, I will discuss a variety of injuries and discuss the effect of the surfaces and other related factors on injuries.

Football injuryI looked for studies comparing knee injuries as a whole that occurred in football on FieldTurf and natural grass. If the studies offered data specifically for ACL injuries on the different surfaces, I included them as well. I will basically compare grass to FieldTurf rather than older-generation artificial turf, as the newest infill surfaces seem to be replacing their predecessors.

The NFL data

In a study performed by the National Football League Injury and Safety Panel, published in the October 2012 issue of the American Journal of Sports Medicine, Elliott B. Hershman et al. reviewed injury data from NFL games played between 2000 and 2009.

They found that the injury rate of knee sprains as a whole was 22% higher on FieldTurf than on natural grass. While MCL sprains did not occur at a rate significantly higher than on grass, rates of ACL sprains were 67% higher on FieldTurf.

Risk factor for ACL tears in college football?

Dragoo et al. reviewed the National Collegiate Athletic Association Injury Surveillance System for injuries between 2004 and 2009 to attempt to identify risk factors for ACL tears in college football. In their study, published in the May 2012 issue of the American Journal of Sports Medicine, they observed that rates of ACL tears were higher on artificial turf than on natural grass. When they isolated infill turf surfaces, such as FieldTurf, the ACL injury rate was significantly higher than on natural grass.

Wide receiver in football practiceIt is worth pointing out that there are studies showing conflicting data. Meyers studied football injuries at 24 universities over three seasons. Comparing all injuries (and not just ACL tears), he found no difference in the rate of knee injuries from games played on natural grass and those on FieldTurf.

Additionally Meyers and Barnhill studied eight high schools over five seasons. They actually found a higher incidence rate of ACL injuries on FieldTurf than on natural grass.

Gino (and others), what does all of this data mean?

I tend to side with the NFL and NCAA data. The study looking at high school football might be a good one, but they only looked at eight high schools and not all NFL teams or NCAA schools. Plus it is possible that the grass conditions at high schools aren’t as good (especially at the end of a season) as those of NFL and NCAA fields. So I at least take these studies to show that ACL injury rates are at least as high – if not actually higher – on FieldTurf than on natural grass.

What we don’t know is exactly why these infill surfaces might lead to more ACL tears. Is it the weather and problems with the surfaces when they get wet? Is it a problem with the interface between the players’ shoes and the turf? Is it a result of increased speed of play due to a uniform playing surface? Much more data on all of these factors in the next few years should help us answer these questions.

Have you torn your ACL or suffered another injury on a football field made of FieldTurf or other artificial turf? Or if you are a doctor or athletic trainer, have you treated injuries from FieldTurf? Share your experiences and thoughts below!

References:

Hershman EB, Anderson R, Bergfeld JA, Bradley JP, Coughlin MJ, Johnson RJ, Spindler KP, Wojtys E, Powell JW. An Analysis of Specific Lower Extremity Injury Rates on Grass and FieldTurf Playing Surfaces in National Football League Games: 2000-2009 Seasons. Am J Sports Med 2012;40(10):2200-2205.

Dragoo JL, Braun HJ, Durham JL, Chen MR, Harris AHS. Incidence and Risk Factors for Injuries to the Anterior Cruciate Ligament in National Collegiate Athletic association football: Data From the 2004-2005 Through 2008-2009 National Collegiate Athletic Association Injury Surveillance System. Am J Sports Med 2012;40(5):990-995.

Meyers MC and Barnhill BS. Incidence, Causes, and Severity of High School Football Injuries on FieldTurf Versus Natural Grass: A 5-Year Prospective Study. Am J Sports Med. 2004;32(7):1626-1638.

Meyers MC. Incidence, Mechanisms, and Severity of Game-Related College Football Injuries on FieldTurf Versus Natural Grass: A 3-Year Prospective Study. Am J Sports Med. 2010;38(4):687-697.

8 Responses to Ask Dr. Geier – Are ACL tears more common on grass or FieldTurf?

  1. Dr. Geier,

    Thank you so much for your illumination of lower injury rates on FieldTurf and natural grass. This is a very important subject that must be studied further.

    As a trainer, I try to do as much research as I can. I am particularly interested in a study that was done at Michigan State:
    M R Villwock, E G Meyer, J W Powell, A J Fouty, and R C Haut
    The effects of various infills, fibre structures, and shoe designs on generating rotational traction on an artificial surface
    Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology March 1, 2009 223: 11-19

    Its findings suggest that too much cleat contact with the infill of turf systems can cause rotational resistance and lead to injury. It found that certain features of a turf system reduce this contact, especially the presence of a nylon root zone and two types of rubber (TPE and ambient). In fact, the authors even state that the combination of a nylon root zone and ambient rubber actually generated LOWER peak torque readings than natural grass did.

    When you look at those findings, it seems that there are certain types of synthetic turf that try to combat what Gino’s players described as “cleats sticking in the ground.”

    My school is going synthetic soon, and because of this I hope that we get Astroturf. That’s the brand that had the nylon root zone in the Michigan State study.

    Dr, Geier, have you or anyone else read this study?

    -Kurt Irving

    • I can’t say that I have. I do think that there is much more research needed about the interaction between the shoes and the newer infill artificial turf surfaces. If anyone else has read the study Kurt mentions, please share your thoughts! Thanks!

      • Indeed an interesting discussion. I want to make some specific comments about the Michigan State Study.

        The MSU research was performed in a laboratory and does not replicate actual in-game condition. Professor Villwock acknowledges in the study itself that lab testing is less reliable than longer-term epidemiological studies.

        The AstroTurf backed MSU research includes both peer-reviewed and non-peer reviewed work. Peer-reviewed is used to describe a process of self-regulation by a profession or a process of evaluation involving qualified individuals with the related field. Peer review methods are employed to maintain standards, improve performance, and provide credibility.

        While the non-peer reviewed research states that FieldTurf produces the highest mean torque compared to all other surfaces, the peerreviewed research from MSU concluded that the mean torque levels on Astroplay and FieldTurf are not significantly different.

        What is difficult for the MSU researchers to explain, and for outsiders to understand, is why the torque measurements were so high.

        The MSU study found that almost every shoe-surface combination tested was over the MSU-quoted 75 Nm safety limit. This included the natural grass surfaces they tested.

        According to Professor Andy McNitt, the Turfgrass Director of Penn State’s Center for Sports Surface Research, the high torque measures make it difficult to confidently make any conclusions about the relative safety of the surfaces tested.

        “These extremely high rotational traction findings for all shoe-surface combinations call into question the testing protocol used in this research. The summary and conclusions of the report confirm that the peak torques measured in the current study exceed injury levels based on cadaveric studies (Hirsh and Lewis, 1965)”.

        “For reference, the peak torque level was established at 75 Nm. The results in the MSU study range between 90 Nm and 120 Nm on the various turf systems – including those offered by AstroTurf. So while AstroTurf is making claims about the relative safety of its product, the study data suggests that all surfaces are effectively unsafe.”

  2. The question mentioned that they practice on grass and only play half their games on turf. I would guess that is common even for teams whose home field is turf. I feel that some of the higher incidence of injury comes from playing on a different surface than what the players are used to. Do you think that there would be a reverse of the numbers if the players practiced on turf and then only played a few games on grass? Likewise do you think that if teams that played on turf would also practice on turf that it would reduce the incidence of knee injuries?

    • Great questions. I do think it is reasonable to study only ACL injuries in games, as the incidence rate for ACL tears is higher in games than in practices across sports and levels. Also collecting accurate data might be more difficult in practice situations across all schools and/or teams. But the questions you raise are good ones and ones which deserve much more research.

  3. Hi All,

    I was a football (soccer) player based in the Philippines where they now have a professional league and built a purposeful stadium to be used to host all league games.

    Previously, they had used the existing grass surfaces and I had only known one player get an ACL tear. the new purpose built stadium has artificial turf with the black rubber. Since it has been used, just over 1 year now I know of 5 players that have suffered ACL tear and meniscal injuries, including myself.

    I don’t feel that this is a coincidence and is somewhat caused by the new surface, which when used with football boots, may increase the likelihood of over extension in the knee given the solid base on which the turf is laid. I would be interested to know if there have been more studies on this and any further theories as to what my cause the higher injury rates on artificial turf?

    Thanks

    Steve

    • There are a lot of studies looking at the different surfaces. Many people think that players’ cleats stick to the turf more than natural grass.

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