FieldTurf, made of polyethylene fibers over a mix of sand and rubber particles, is used by 21 of the 32 NFL teams for either their practice or playing fields, according to the company's website, as well as for some high school and college fields. It's easier to maintain than natural grass, and can hold up indoors in dome stadiums.

Surveys have shown NFL players generally prefer FieldTurf over older versions of artificial surfaces, and studies of college and high school athletes found head, knee and shoulder injuries occur with the same frequency on FieldTurf and grass.

But the new study found anterior cruciate ligament (ACL) injuries, in particular, happened at a higher rate on the artificial surfaces.

"I think the main messages here are that different surfaces behave differently, and that injury rates can be different on different surfaces," said Dr. Elliott Hershman, the study's lead author and chairman of the NFL Injury and Safety Panel.

It's also possible that athletes' footwear, or the surfaces they're used to practicing on, play a role in game-day injury risk, according to the researchers.

"I think we need to look at factors that we can modify in our constant quest to reduce injury rates," Hershman, also the chairman of orthopedic surgery at Lenox Hill Hospital in New York, told Reuters Health.

He and his colleagues used data from the NFL's injury surveillance system, which covered 2,680 games played on grass or FieldTurf between 2000 and 2009.

They found players suffered 1,528 knee sprains and 1,503 ankle sprains during those games, and both types of injuries were 22 percent more common in games played on FieldTurf.

In particular, ACL sprains - often considered season-ending injuries - were 67 percent more common on FieldTurf than on natural grass.

The researchers wrote in the American Journal of Sports Medicine this week that they can't prove anything about FieldTurf, in particular, was behind the higher injury rate.

Michael Meyers, an assistant dean at the College of Western Idaho, said it's hard to know what else came into play during injuries - such as weather and where on the field injures took place.

Meyers conducted the research on FieldTurf in college and high school athletes, which he said was partially funded by the company.

"We didn't find any significant differences between the two surfaces, which makes them both a viable option," he told Reuters Health.

When it comes to natural grass, he said, this study may not be representative of the surface most non-professionals are playing on.

"There's a big difference between an NFL field, which is pristine and prime, and every other field in the country," Meyers said. That could tip the injury balance in favor of grass in a study limited to the pros.

Darren Gill, Vice President of Global Marketing at FieldTurf, also responded to the study in a statement to Reuters Health, saying the findings "run contrary" to data supporting the safety of artificial turf.

"Third party expert analysis of the 'NFL Study' concluded that poor study design drove the flawed, outlier, findings. New field buying patterns from the NFL continue to support turf," he added.

Hershman said the results call for more research on injury rates on grass and turf for a range of sports and levels of play - as well as on what was happening on the field at the time of NFL injuries that might explain injury differences by playing surface.

SOURCE: bit.ly/UTmW0v American Journal of Sports Medicine, online September 12, 2012.

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