November 2014

Dorsiflexion and knee injury risk: Implications for ankle bracing

shutterstock_216334837Some evidence suggests that, if ankle braces limit athletes’ motion in the sagittal plane, the risk of knee injury could be increased, but other studies have found no association between ankle bracing and knee injury rates. The conflicting findings have made for a clinical conundrum.

By Cary Groner

Bracing is a well-established and effective approach to preventing ankle sprains and helping them heal, but in recent years, as long-term prophylactic uses have increased, trainers and researchers have begun to wonder if the strategy may pose risks higher up the kinetic chain.1 One concern is that restricting ankle motion may partially deflect ground reaction forces up into the knee, overloading it, displacing it in the frontal plane, and putting it at increased risk of injury. Of the seven million doctor visits associated annually with sports injuries, knees are the most common complaint, so it’s not a trivial worry.2

One key variable in this discussion appears to be the extent to which ankle braces, which are designed primarily to limit inversion and eversion motion, also potentially limit movement in the sagittal plane. Another is the extent to which studies of individuals with intrinsic limited ankle dorsiflexion can be extrapolated to athletes wearing prophylactic ankle braces.

“Certainly we know that ankle braces are very effective in mitigating risk for ankle injury,” said Darin Padua, PhD, ATC. “But if they are very restrictive in terms of the sagittal plane motion at the ankle, thereby causing reductions in dorsiflexion, could they have unintended consequences?”


Ankle dorsiflexion and the knee

This January in LER, Padua and colleagues reviewed evidence that limited ankle dorsiflexion range of motion (ROM) may contribute to altered frontal plane knee biomechanics and increase knee injury risk as a result.3 And although some studies do suggest that restricted ankle dorsiflexion may increase the risk of chronic knee injuries such as patellar tendinopathy,4 it’s less clear whether it may also worsen the danger of acute injuries such as noncontact anterior cruciate ligament (ACL) tears. Research suggests, however, that changes in ankle ROM could conceivably contribute to a mechanism for these as well as medial collateral ligament injuries, meniscal injuries, or chronic injuries such as patellar tendinopathy or patellofemoral pain syndrome.3 And, because ankle dorsiflexion motion absorbs up to half of the kinetic energy associated with a jump landing,5 restricted ankle motion could lead to greater loads on the knee in sports that require jumping.

“In our lab, we have seen restricted ankle dorsiflexion motion in individuals who have altered lower extremity movement patterns—and in particular, when the knee collapses into a valgus pattern,” said Padua, who is professor and chair of the Department of Exercise and Sport Science at the University of North Carolina at Chapel Hill. “We think there is a compensation for that lack of dorsiflexion via increased valgus or varus motion at the knee.”

In a recent study in the Journal of Athletic Training (JAT), Padua and his colleagues compared knee and ankle kinematics during tasks such as a weight-bearing lunge and squatting in individuals with limited ankle dorsiflexion ROM versus those without ROM limitations.6 They reported that those with limited ankle dorsiflexion displayed less knee flexion, and had greater knee varus displacement, during squatting tasks than those with normal ROM. In contrast, in the weight-bearing lunge, those with greater ankle dorsiflexion ROM displayed more knee varus displacement than those with limited ankle dorsiflexion, suggesting that what happens at the knee is partially dependent on the maneuver performed. Neither cohort displayed unusual knee valgus motion, which is usually considered a risk for ACL injury.

Padua isn’t sure what limits ankle movement, but he has theories about it.

“I think there are a couple of primary factors that may be restricting the available ankle dorsiflexion range of motion,” he told LER. “One could have to do with soft tissue; the calf muscles may be tight or overactive, which could be addressed with some form of myofascial release along with basic stretching. Also, we often see a joint restriction that requires a mobilization maneuver of the ankle, particularly in someone who’s had an ankle sprain.”

Other researchers have reported similar findings. For example, in a paper published in Knee Surgery, Sports Traumatology, Arthroscopy this August, the authors studied 23 female college soccer players and found that those with less ankle dorsiflexion flexibility exhibited greater peak knee abduction moments and angles, as well as less peak knee flexibility, during jump landings.7

Cause and effect isn’t always clear in such situations, however. For example, are altered knee biomechanics a result of the decreased ankle dorsiflexion ROM, or do both simply coexist in people with a certain biomechanical profile? The question is important in determining whether ankle braces might cause the same problems that inherently limited ROM does.

Proximal effects of ankle bracing

According to Padua, bracing could result in compensatory motions at the knee and hip, causing altered biomechanics and loads—and perhaps increased risk of injury.

“We don’t know yet,” he said, “but based on what we know about ankle dorsiflexion in general, and how it influences lower extremity biomechanics, it’s something worth considering.”

Other researchers have sought to shed light on the issue. For example, one paper reported that prophylactic ankle braces were associated with reduced energy absorption by the ankle during jump landings.8 That study focused solely on ankle joint kinematics, but it’s reasonable to assume that forces not assimilated by the ankle have to be absorbed somewhere else.

Photo courtesy of Topical Gear

Photo courtesy of Topical Gear

A Japanese study published in Knee this year9 found that when 30 healthy volunteers wore a custom ankle brace designed to restrict ankle dorsiflexion ROM, knee joint kinematics and kinetics in both the sagittal and frontal planes were affected—differences that were observed with ankle dorsiflexion restriction of approximately 8°.

And a paper from this past summer reported less ankle dorsiflexion in 30 individuals who’d suffered an ACL injury than in 30 controls who had not.10 But again, such studies describe correlation rather than cause, so it’s difficult to draw conclusions about their clinical relevance.

One of Padua’s coauthors on the JAT paper, Rebecca Begalle, PhD, is an assistant professor of kinesiology at Illinois State University in Normal who focuses on preventing ACL injuries and improving outcomes after they occur.

“I definitely think that when we have restrictions at the ankle, it impacts what we are doing at the knee and the hip, because we need to gain that range of motion somewhere,” Begalle said. “But it’s not as simple as it seems; the true relationship is elusive. And, in a weight-bearing position, if you have limitations in ankle dorsiflexion, it seems that you also utilize knee flexion less well.”

One issue is that ankle braces are designed primarily to restrict frontal plane motion—inversion is the most common cause of sprains—but restricted sagittal plane motion at the ankle may pose the most risk for the knee. Most braces also restrict sagittal motion, of course, though the effect appears to be small, and those with hinged designs have even less influence.

Findings in bracing’s favor

Some research concludes that ankle bracing may not have significant effects at the knee. For example, in a 2012 paper Jacob Gardner, PhD, and his colleagues reported that when 11 young women performed single-leg drop landings in both unbraced and braced-ankle conditions, wearing a boot brace reduced ankle work, but did not change relative knee or hip work compared with the nonbraced condition.11 Wearing a hinged brace was not associated with significant differences in relative work compared with the nonbraced

“I think a lot of the differences in findings have to do with how the labs are set up, how participants are asked to land, things like that,” said Gardner, who is an assistant professor of kinesiology at Biola University in La Mirada, CA. “In general, although I think there’s a risk for knee injury [associated with ankle bracing], I don’t think the risk is for acute injury. Perhaps if someone were to continuously wear a brace over a long period of time, they might be at more risk due to stress on the articular cartilage, the meniscus, or the ligaments surrounding the knee joint.”

Other research also undercuts the argument for an increased risk of acute injury. In a 2013 study, for example, researchers had 15 elite female volleyball players perform a series of straight-line and lateral volleyball tasks both unbraced and wearing a hinged ankle brace.12 They measured knee range of motion, peak knee anterior-posterior and medial-lateral shear forces, and peak ground reaction forces (GRF) between initial contact with the force plate and toe-off. The authors concluded that ankle bracing had no significant effect on knee kinematics or GRFs during the straight-line tasks, and that it reduced knee lateral shear forces during the lateral tasks.

Similarly, in papers published in The American Journal of Sports Medicine in 2011 and 2012, Timothy McGuine, PhD, ATC, and colleagues at the University of Wisconsin in Madison examined the effect of lace-up ankle braces on injury rates in thousands of high school basketball players of both sexes, and male football players, respectively.13,14 In those studies, braces were associated with a significantly reduced incidence of ankle sprains: for basketball players, those who wore braces had a sprain incidence just 33% of those who didn’t; for football players, the relative risk was 43%.

McGuine, who is a senior scientist at the university’s School of Medicine and Public Health, told LER that there was no difference in the incidence of knee injuries associated with bracing, however.

“Looking at data from roughly three thousand subjects, half of them with braces and half without, in both football and basketball, we saw no difference in acute knee injuries,” he said. “That includes acute ACL tears, patellar dislocations, meniscal tears—those types of injuries. Over the course of the season, for example, in the basketball players, we had five ACL tears in those who wore ankle braces, and five in those who didn’t. We just found no correlation between bracing and knee injuries.”

Clinical considerations

Ultimately, clinical decisions about ankle bracing in athletes come down to weighing the potential preventive benefits against the potential risks.

Photo courtesy of DJO Global

Photo courtesy of DJO Global

“There are certainly instances where wearing an ankle brace is beneficial,” said Becky Begalle. “People with chronic ankle instability or a history of injuries need added protection.”

Jake Gardner concurred.

“If someone has chronic ankle instability—brace that person,” he said. “It’s more important to take care of the ankle than to worry that somewhere down the line they might incur a knee injury. But if someone doesn’t have ankle trouble, probably the biggest threat is restrictions to dorsiflexion range of motion. That’s where energy from a landing is absorbed, and if you restrict that motion it can affect the kinetic chain, which is why I think articulated braces have less impact at the knee.”

In fact, this line of research could potentially create opportunities for brace designers.

“By restricting ankle motion, we’re definitely changing biomechanics, which could be one contributing factor to loading at the knee that could put someone at greater injury risk,” Begalle said. “Maybe braces should be designed slightly differently, to protect the lateral structures at the ankle without inhibiting range of motion. Hinged braces are one way to do that, but they’re usually relatively bulky, thick devices that athletes aren’t that comfortable with.”

Researchers and clinicians have begun to explore what such findings mean in practical terms. For example, in a recently published biomechanical comparison of three ankle braces (two hinged and one nonhinged) with and without rotation in the sagittal plane, German researchers reported that all three braces restricted frontal plane motion about equally in dynamically induced foot inversions on a tilt platform.15 One hinged model, a neoprene sock with a flexible hinged outer cast, did have more inversion restriction than the nonhinged semirigid brace or the other hinged model, a stirrup-style design with a polypropylene shell. The hinged models allowed greater passive plantar flexion than the nonhinged one, however, leading the researchers to recommend the softer hinged brace or the nonhinged brace for those needing more support, and the stirrup-style hinged brace for prophylactic use because it was less restrictive in terms of sagittal plane mobility but still stabilized the ankle sufficiently during inversion.

The long view

Athletes often express concern about unintended effects of long-term bracing, according to Lindsay DiStefano, PhD, an assistant professor of kinesiology at the University of Connecticut in Storrs.

“Some athletes are encouraged to wear ankle braces prophylactically, and there’s pretty good evidence that they reduce the risk of injury,” DiStefano said. “But they wonder if daily wear is going to change the way they move. They worry that their muscles won’t be as reactive when they remove the brace.”

Photo courtesy of DeRoyal

Photo courtesy of Darco

In response to such concerns, DiStefano and her colleagues conducted a study in 37 healthy young athletes, who were randomized to either wear a lace-up ankle brace (n = 19) or not (n = 18) during all recreational activities for eight weeks. They discovered that, although the braces restricted sagittal plane ROM at the ankle, knee flexion increased on landing and vertical ground reaction forces did not change.

“We tested people before they put on the brace, then as soon as they put it on,” DiStefano explained, adding that her team assessed the participants for both movement parameters and muscle activation, then repeated the tests two months later.

“We showed that eight weeks of wearing an ankle brace regularly had no effect on how someone moved or how their muscles functioned,” she said. “Any time we put on the ankle braces, acutely or long-term, we saw that same effect—restricted ankle dorsiflexion motion, but increased knee flexion motion at initial contact.”

In other words, the athletes’ knees compensated for decreased ankle dorsiflexion by bending more, rather than slipping into varus or valgus displacement. DiStefano considers the result telling, given that most of the studies that appear to contradict these results were conducted in individuals with inherently limited ankle dorsiflexion ROM rather than a limitation imposed artificially by bracing.

Other research has reached similar conclusions. In a 2013 paper published in the Journal of Applied Biomechanics, for example, the authors had 16 female athletes perform drop landings both braced and unbraced.16 When the athletes wore braces, there was less external rotation at the ankle and knee, and ground reaction forces increased. Participants’ knees flexed more on landing, but the braces didn’t affect motion in the frontal plane.

“The literature has shown that when someone has ankle dorsiflexion motion—when the joint has a capsular restriction or a musculotendinous restriction, for example—that that can affect compensations up the kinetic chain,” DiStefano said. “But when an ankle brace is what restricts dorsiflexion, I don’t know that we have the evidence that it has the same effect. Tim McGuine’s studies didn’t show any correlation between ankle bracing and an increase in knee injuries, which would make me think that the restriction caused by the ankle brace is not significant enough to change knee kinematics.”

Darin Padua, though cautious about drawing conclusions while evidence is still being gathered, generally agreed.

“Braces are designed to limit frontal plane motion, but to not significantly restrict dorsiflexion—at least enough to make the kind of difference we see in those with inherent physical restrictions,” he said. “It’s also possible that since braces do limit inversion and eversion, perhaps that limits how much the knee can compensate in the frontal plane motions as well. It could be a combination of those two things—a lack of significant effect on dorsiflexion, and ankle stabilization that helps the knee.”

Moreover, DiStefano pointed out, the fact that ankle injuries can induce inherent limitations in ankle dorsiflexion ROM, and the demonstrated associations between these and the resulting frontal plane displacement at the knee, would seem to support ankle bracing to protect the knee.

“We know that a sprain can restrict the ankle joint, which could cause these bad compensations up the kinetic chain,” she said. “The bottom line is that there’s no evidence to say you shouldn’t wear an ankle brace because you’re worried about your knees. In fact, you should wear them, so you don’t sprain your ankle and end up with restrictions that could lead to other problems.”

Asked who, then, should wear ankle braces and under what circumstances, DiStefano described her personal hierarchy.

“If you have a history of sprains, and you’re in a high-risk sport such as basketball or volleyball, you should wear them,” she said. “If you have a history of sprains, regardless of your current sport, you should probably wear them. And, if you don’t have a history of sprains but play a high-risk sport, you should at least consider wearing them. Until we come up with better evidence about other ways to prevent injuries, such as neuromuscular training, ankle braces still look like the best option.”

Cary Groner is a freelance writer in the San Francisco Bay Area.

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One Response to Dorsiflexion and knee injury risk: Implications for ankle bracing

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