September 2013

The NFL’s ACL issue: Experts debate contributing factors

In the moment: Sports medicine

itm-sportsBy Jordana Bieze Foster

A flurry of anterior cruciate ligament (ACL) injuries in National Football League (NFL) players early in the preseason has medical experts theorizing about the contributing factors and what can be done to protect players in the future.

The first two weeks of training camp resulted in at least 15 ACL tears, each of which ended a player’s season before it had even started. Although the extent to which this season’s early ACL tear rate may have exceeded that of the 2012 season is unclear, the injuries occurred in such rapid-fire fashion that media outlets, medical experts, and even league officials couldn’t help but take notice. Atlanta Falcons CEO and NFL competition committee chair Rich McKay told USA Today on August 12 that “there have been more ACL injuries than ever,” and said the league would have its analysts investigate whether the number of ACL injuries this season actually constitutes more than a coincidence.

In looking for variables that could be contributing to ACL injuries in the NFL, many experts and analysts have pointed to aspects of the collective bargaining agreement (CBA) between the league and players, the signing of which in August 2011 ended that year’s player lockout.

The new CBA mandates a significant decrease in the length of the offseason training program, number of “organized team activities” (offseason training sessions), and number of full-contact practices. In addition, the CBA limits players’ access to team training facilities and medical personnel during the offseason.

The new rules, perhaps ironically, are designed to protect players—the reduced physical contact is intended to decrease the risk of concussion, and the reduced training volume is intended to decrease the risk of overuse injury and general wear and tear. But some believe the limitations may have unintended consequences when it comes to risk of ACL injuries.

9ITM-sportsMed-shutterstoc-copy“The decrease in mandatory offseason training activity time and minicamp sessions gives players more time on their own during the critical preconditioning time before training camp. Some players may be more diligent about their diet, fitness, and conditioning during that time than others,” said Jene Bramel, MD, who writes about football injuries in his “Second Opinion” blog for “There’s also a difference between being in peak muscle fitness and cardiovascular shape and being in football shape. A player may pass his conditioning tests without difficulty, but there’s a physical and mental readiness necessary to prepare the body to take hits at unexpected angles and handle other football-related stresses. Some players believe that padded practices are necessary to achieve a comfort level.”

Tim Hewett, PhD, director of the Ohio State University Health and Performance Institute in Columbus, noted that the ACL injury patterns in the NFL this season are reminiscent of the increase in ACL injuries seen after the 2011 National Basketball Association lockout and the increase in Achilles injuries that occurred after the 2011 NFL lockout (see “Lockout lessons: NFL Achilles injuries spark debate,” November 2011, page 15). Athletes had no access to team training facilities during both lockouts, so it makes sense that the training restrictions for NFL players mandated by the CBA would have a similar effect, he said.

“This number of ACL injuries in the preseason is way beyond what you’d normally expect, and now there have been three instances of what appear to be significant anomalies in injury patterns. When you put the three together, you may have something real,” Hewett said. “There is extremely strong evidence now showing we can reduce the risk of noncontact ACL injuries through training. Could we make the leap to say in the absence of that kind of training the injury rate would go up? I think logically we could say that.”

Whereas altered training practices may have contributed to rates of noncontact ACL injury, a change in the on-field rules—again, intended to protect players from concussion—may be inadvertently increasing the risk of ACL injuries resulting from contact between players. A 2010 rule established fines for tackles targeting an opponent’s head or neck under certain situations. But some defensive players, in an effort to avoid such infringements, have compensated by focusing their tackles on their opponent’s legs, in turn putting the knees at risk.

“The trend toward tackling low is likely to cause more leg injury, including ACL tears. That may be a player-driven trend rather than a change in coaching, however,” Bramel said. “If so, it’s possible that an increase in missed tackles or in concussion in defensive players could reverse that trend quickly.”

Both Bramel and Hewett suggested that newer-generation artificial playing surfaces may also be contributing to ACL injury in NFL players, citing a 2012 study conducted by the league’s Injury and Safety Panel that found a 67% higher rate of ACL sprains on artificial turf than on grass (see “Artificial surfaces evolve, but safety debate persists,” May 2013, page 57). An ACL sprain may be less severe than a tear, but the mechanism of injury is essentially the same, Hewett said.

“After that study came out, I’ve only heard of one NFL owner who’s changed his turf field back to grass,” Hewett said. “To put in a turf field it’s six or seven hundred thousand dollars, and to put grass back it’s probably less. If you’re seeing players who earn ten million dollars pop their ACLs, wouldn’t you want to put grass back in your stadium?”

Neuromuscular training programs have been demonstrated to reduce the incidence of ACL injury in younger athletes, but if NFL teams are using similar programs in their training, that hasn’t been made public knowledge. It’s also unclear whether such programs would have similar preventive effects in NFL players, in whom some risk factors may be different than in the populations studied to date.

But Hewett and colleagues at OSU intend to find out. They screen all incoming Buckeye athletes—many of whom end up playing in the NFL—for biomechanical ACL risk factors and will follow them longitudinally to see whether any baseline screening variables are predictive of ACL injury.


Hershman EB, Anderson R, Bergfeld JA, et al. 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.

2 Responses to The NFL’s ACL issue: Experts debate contributing factors

  1. Liz Witten says:

    This is a great product to prevent any long term or short term knee injuries. My husband is a triathlon running and has always had knee troubles. Better to be safe than sorry when it comes to these kinda of injuries, they could be life long if severe enough. This brace is comfortable and effective. I would highly recommend to any athlete.

  2. Not only is artificial turf implicated, but also, for those players playing on grass, the type of grass is highly implicated in ACL ruptures in Australian Rules Football (Orchard et al Br J Sports Med 2005;39:704–709). Bermuda (couch) and kikuyu are particularly implicated, with Rye grass demonstarting statistically lower ACL injury rates. It seems pretty clear that shoe surface traction in all codes of football is an important factor in the generation of ACL injury

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