Jan 29, 2015
Analyzing ACLs Beyond Gender

By Mike Phelps

It is widely accepted that females are more prone to ACL tears than males, but the specific reasons behind the increased risk are not yet fully understood. A recent consensus statement from the NATA says the association hopes to help future researchers answer these questions, while also stating a need for fewer gender studies, which look simply at sex differences.

According to the statement, “Although much has been learned about characteristic sex differences in neuromuscular and biomechanical function over the past 12 years, we still know very little about the underlying causes of these differences or whether many of the observed differences truly reflect an increased injury risk for the physically active female.”

Sandra Shultz, PhD, ATC, CSCS, Associate Professor and Director of Graduate Study at the University of North Carolina-Greensboro, who co-authored the statement, says that while the differences between males and females in regard to ACL injuries have been established, whether or not those differences are really causing ACL injuries has not. “We’re also not sure which of the differences may be the most important factors causing ACL injuries,” she says. “Over and over again, literature has identified that males and females are different on a number of factors. We need to really begin to look at some of these factors within a particular sex and see how they influence movement and joint function.”

Shultz says the statement, which is a combination of the most current research as well as an update on existing literature, will help direct where future research needs to go in order to unlock the mystery of what causes greater occurrences of ACL injuries in females. “There are a lot of different ways that males and females have been described as being different in their structure and how they move, so automatically it’s often assumed that because females are this way and are more prone to injury, it’s these movement profiles that place them at a greater risk for injuries,” she says. “But we haven’t always identified that. We haven’t always taken that all the way through and found that it truly is predictive of injury risk.”

As an example, Shultz provides that it is often heard that females are more quadriceps-dominant than their male counterparts. Since the quadriceps are thought to create excessive forces, that’s automatically one of the factors that places females at risk. “But we’ve yet to study if this quadriceps dominance is truly a predictor of injury risk,” she says. “We haven’t connected the dots very well.

“It’s time to quit describing all these sex differences in movement, neuromuscular and biomechanical function,” she continues. “We now need to take a step back and ask, ‘What are the underlying factors that explain these differences?’ We then need to take it to the next step of whether they are truly predictive of injury risk. We kind of started in the middle, described all these differences, and now we assume that they’re related to injury risk, but we haven’t really taken it all the way through.”

Moving forward, Shultz hopes to see researchers go away from studies that only look at one or two risk factors at a time. Instead, she’d like to see studies that look at various factors in combination. “We really need to look and see how the factors interact with one another if we’re going to understand how they together impact injury risk,” she says. “It’s probably not any one of those things in isolation. It’s only when we begin to look at those factors in combination that we’ll really understand the injury risk equation.”

To accomplish this, Shultz sees two potential types of studies. First, researchers can conduct prospective studies that measure individuals on a host of factors, then see who gets injured. Another option is to do a retrospective, which is done after an injury occurs by matching the injured individuals to control cases–uninjured individuals–and see how the cases differ on a number of variables.

“The challenge with doing this prospectively is we could take three hours to measure each person, and we would have to measure thousands of people to yield a sufficient number of ACL injuries to be able to make sense of the data,” Shultz says. “And the problem with the latter is, if you’re interested in looking at knee laxity, you really can’t look at that anymore once the knee is injured, because the variable or the measuring point has changed.

“It’s challenging,” she continues. “A prospective study is probably the best approach, but it would take a huge effort and a lot of researchers and participants. I think that’s kind of why we are where we are. We’ve got multiple people studying this, but few are studying it on a large enough scale to really make an impact.”

For more on ACL injuries, including how to help prevent ACL tears, be sure to check out our feature in the November issue of Training & Conditioning.

Mike Phelps is an Assistant Editor at Training & Conditioning.

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