NEW YORK -- An NFL panel found that certain serious knee and ankle injuries happen more often in games played on the most popular brand of artificial turf than on grass.

The league's Injury and Safety Panel is presenting its study Friday at the annual meeting of the American Academy of Orthopaedic Surgeons in New Orleans.

The report examined the 2002-08 NFL seasons, comparing games played on grass to those on FieldTurf. It found that the rate of anterior cruciate ligament injuries was 88 percent higher in FieldTurf games -- a conclusion the manufacturer of the synthetic field hotly disputes.

Panel chairman Dr. Elliott Hershman, a Jets team orthopedist, said it's too soon to make any recommendations on what surface teams should choose. More research is needed on issues such as whether players are wearing the right types of shoes on artificial turf.

"At this point we want to stimulate more discussion," he said.

The panel has presented its findings to league owners, the NFL Players Association and companies that make artificial turf. The study has been submitted for publication.

"The paper is designed to stimulate further discussion, inquiry, and improvements in playing surfaces," league spokesman Greg Aiello said. "It does not draw any conclusions about the cause of the injuries analyzed. Our panel states in the report that additional analyses, data from future NFL seasons, and studies of injury rates on synthetic turf and natural grass surfaces, including for other athletic populations and levels of football, are needed before any conclusions can be drawn or recommendations made."

Nine NFL stadiums currently have FieldTurf (Cincinnati, Detroit, Indianapolis, New England, Atlanta, Minnesota, St. Louis, Seattle and the new Meadowlands Stadium).

NFL teams began switching from the old carpet-style turf to the springier, more grass-like surface in 2000. By the end of the 2008 season, 14 stadiums used a brand of next-generation turf, while the rest had grass. Too few games were played on brands other than FieldTurf to include them in the study, Hershman said.

The panel started to notice a higher rate of injuries on the new turf in evaluating the data the NFL compiles each season, Hershman said. Once enough games had been played on the newer surfaces to do a scientific analysis, the panel found that ACL injuries and a more serious type of ankle sprain occurred at a higher rate that is statistically significant.

The rate for the ankle sprains was 32 percent higher on FieldTurf than on grass. MCL injuries and a less serious type of ankle sprain also happened more frequently, but the difference was not statistically significant.

Hershman noted the NFL research may not apply to lower levels of football or to other sports.

FieldTurf president Eric Daliere argues that the panel's methods are faulty and cites research by Montana State professor Michael Meyers that has been published in The American Journal of Sports Medicine. Meyers' work, though, has only looked at high school and college football, and not the NFL. FieldTurf paid for Meyers' recent study that found lower overall injury rates for college games played on the surface.

"Michael Meyers has come to a very different conclusion on a different level and his is a real study, not just a report," Daliere said. "He mentions poorly designed [analyses] -- and this is the kind of work he does -- and that the statistical analysis by the [NFL] panel was also flawed.

"I don't put a lot of weight in it and think if is unfortunate it is coming out this way at this time."

Meyers said in an e-mail to The Associated Press that he told the NFL in 2008 "there are too many glaring omissions and biases in the study to reach any valid conclusions." He questioned why certain factors that could influence injury rates were not included and noted that some teams didn't play any games on FieldTurf during some of the seasons studied.

Other university scientists and statisticians also expressed concerns, he said, and the panel withdrew its report after those meetings.

Hershman disputed that.

"Nobody withdrew anything," he said. "We actually did some review of our data based on some of the thoughts they raised, and we validated our data. Because we did all that, we now feel our data is valid, relevant and statistically significant."

FieldTurf promotes the safety benefits of its product on its Web site.

"As a company," Daliere said, "the safety of the athletes really is in our DNA. It's what FieldTurf focused on from the very beginning when we replaced traditional Astroturf with something dramatically safer."

Daliere mentioned that Hershman's team, the Jets, will have FieldTurf in its new stadium.

A close look at the panel's data may not have much effect on NFL teams who know they can save money on maintenance in the long run by using FieldTurf rather than grass. The study estimated that if every stadium with grass were to switch to FieldTurf, that would result in only five additional ACL injuries per season across the NFL because of the infrequency of the injury.

The NFLPA's biennial poll of its players last year showed that their four favorite fields were grass: Arizona, Tampa, San Diego and Carolina. Four of the next six were FieldTurf.