In the ongoing battle against inversion ankle sprains in basketball and other sports, high tops are old news. But shoe designers have begun to investigate other ways that shoes might play a role in preventing sprains rather than contributing to the problem.
By Cary Groner
In the ongoing war against lower extremity injuries faced by athletes and the practitioners who treat them, shoes are viewed a bit like Pakistan: as necessary but untrustworthy allies. In basketball and football, players have become bigger and faster, and there’s no doubt that shoes provide cushioning, traction, and protection from the punishing effects of the court and field that are amplified by size and speed.
But shoes have credibility issues. It’s difficult to make them fit tight enough to keep the foot from sliding around inside—and if they are tight enough, they’re usually uncomfortable. That interior movement can make inversion more likely, clinicians say; and by elevating the foot on a sole, shoes increase the lever action when inversion occurs, raising the risk of ankle sprains.1
As a result, shoe designers have begun to investigate how shoes might become part of a preventive solution to sprains, rather than contributing to the problem.
Shoe highs and lows
The first step involves determining which features of shoes may raise or lower the risk of sprains. The control condition, in this case, is provided by Mother Nature: it’s going barefoot. It’s not impossible to sprain your ankle when you aren’t wearing shoes—the author of this article has done it—but it takes a level of uncoordination more common in writers than in professional athletes.
“If you put your bare foot on the floor and roll out into inversion, there are twenty-eight bones and thirty-three joints, and a hundred and twelve ligaments in that foot that are very mobile, and that make it difficult to sprain your ankle,” said Howard Hillstrom, PhD, director of the Leon Root Motion Analysis Laboratory at the Hospital for Special Surgery in New York City. “But when you put on a shoe, it reduces that freedom, so all those joints and articulations are no longer able to adapt as well. Then, if you stand in the shoe and roll
it out in the direction of inversion, you get to the edge of the sole, where you feel this marginally stable point. If you go further—boom! You’ve sprained your ankle. That point of instability arises artificially due to the edge of the shoe under the lateral aspect of the foot.”
But soles provide the cushioning that helps keep jumping athletes, particularly basketball players, from hobbling around on blown-out knees before they’re 30, so no one is seriously suggesting they be discarded in favor of playing barefoot. Instead, as a means of reducing sprains, researchers are trying to determine how shoes could increase stability rather than undermine it.
For decades, high-top shoes were thought to help. It stood to reason that lacing up the canvas or leather would support the ankle and prevent sprains, but it turns out this may not actually be true.
As early as 1993, researchers at the University of Oklahoma reported that high-tops offered no advantages in terms of sprain prevention over low-tops in collegiate intramural basketball players.2 This finding was echoed in a 2001 Cochrane review of 14 randomized trials, which also concluded that interventions such as orthoses and braces did prevent ankle ligament injuries.3 And, although one study showed that high-tops reduced the rate and amount of ankle inversion compared to low-top shoes, it didn’t address whether the difference correlated with lower sprain rates.4 In May 2010, moreover, a sports columnist at the Wall Street Journal declared that high-tops were on the way out, partly due to lack of evidence that they prevented sprains. He noted that National Basketball Association star Kobe Bryant’s new Nike-designed shoes were low-tops, a style for which sales had risen to 29% of the overall market from just 11% in 2002.5
According to Michael Lowe, DPM, team podiatrist for the NBA’s Utah Jazz, shoe-top height may be a red herring.
“There’s still so much motion that occurs at the interface of the shoe and foot that no matter what, you can still have a lot of inversion or eversion occurring within the shoe itself,” he said. “You’re just not going to prevent that.”
Eric Bluman, MD, PhD, an assistant professor of orthopedics at Harvard Medical School, believes that focusing on shoe height in terms of structural support may miss the point.
“One important thing some shoes may do is increase proprioceptive feedback,” he pointed out. “Something that’s stretched or pulled when you invert your ankle [short of causing injury] may increase your sensation and awareness of those positions, and that may contribute to a lower incidence of ankle sprains.”
Part of the rehabilitation protocol recommended by Bluman and others, in fact, includes strengthening the peroneal musculature on the ankle’s lateral side and reestablishing and enhancing proprioceptive function.
Jarett Reinhartz, CPed, who practices at FootCareExpress in Miami, told LER that high-tops may indeed improve proprioception.
“That may help address the mechanism that causes sprains, by telling the foot to change directions,” he said.
His colleague, Charles Mutschler, DPM, the company’s medical director, added, “A J-strap [tape] around the plantar aspect of the heel, up the lateral course of the peroneal tendon behind the lateral malleolus, effectively does the same thing as a high-top shoe—it increases the reactivity of the peroneal muscles, which helps prevent ankle sprain.”
Lowe agreed that proprioception—whether gained via a shoe, a brace, or training—is an essential element in preventing sprains and returning athletes to health after they occur.
“We see significant loss of proprioception through multiple injuries to the ankle,” he said. “When players get that back, we don’t see the recurrence of as many sprains. That’s trainable, and most teams are now trying to build in proprioceptive exercise [e.g., using balance balls] with their daily stretching programs. You’re not strengthening structure per se; you’re just letting structure talk.”
Lowe believes, in fact, that the current popularity of prophylactic ankle bracing may have more to do with neuromuscular effects—including proprioception—than with support, and some research bears this out. For example, a study in the British Journal of Sports Medicine reported that lace-up ankle braces facilitated the amplitude of the peroneus longus stretch reflex, and that the effect did not diminish over the eight weeks of the study.6
Absent analogous studies, however, the extent to which such results can be applied to footwear remains to be seen.
The chain gang
One of the questions clinicians have about shoe designs that purport to reduce ankle sprain risk is whether redirecting forces up the kinetic chain may have deleterious consequences. Downhill skiers, after all, have their ankles locked in place by rigid plastic boots, and sprains are rare. They destroy knee ligaments with alacrity, however.
“If you stop the ankle sprain completely, that mechanism and force is going to be translated somewhere else in the body—to the lower leg, the knee, or the hip,” Mutschler said. “And a knee injury may be much more severe than an ankle injury.”
Tim McGuine, PhD, ATC, a senior scientist in the Orthopedic Sports Medicine Program at the University of Wisconsin in Madison, has studied the effects of both balance training and ankle bracing extensively. In two recent controlled trials currently in press, McGuine and his colleagues looked at whether ankle bracing increased the risk of knee injuries in male and female high school basketball players, among other things.
“We did see a risk reduction for ankle injuries, but no difference in the incidence of knee injuries between those who wore braces and those who didn’t,” he said, while emphasizing that the research was preliminary. “I’m leaning toward thinking that we have this proprioceptive neuromuscular feedback effect, and that we’re getting the muscle to fire off a millisecond faster.”
McGuine noted, moreover, that even though the bracing reduced the risk of ankle sprains, the sprains that did occur were just as severe in the bracing group as in the controls, reinforcing the notion that the brace’s effect involves neuromuscular feedback rather than strengthening.
“You could do the same kind of studies on shoes,” he said, noting that no one has, so far. “Get the baseline measurements on these people, have a subgroup without the intervention shoe, then do the neuromuscular testing at one month, three months, six months, and see what’s happening. If you had something in the shoe design so that as the ankle started to roll over, it stimulated feedback, I’d think that over time you’d help train the muscles and improve reaction times.”
For Daniel Fong, PhD, a research assistant professor in the Department of Orthopedics and Traumatology at Prince of Wales Hospital in Hong Kong, sprain-preventive footwear needs to move beyond proprioceptive response into what he terms an “active feedback correction system.”
“We’ve found two etiologies for ankle sprain,” he said. “One is incorrect landing, where you land with the foot inverted, which exerts a very quick, twisting torque to the ankle joint. The second is the delay in muscle reaction time at the lateral shank, in the peroneal muscles.”
To remedy that, Fong has developed an anti-sprain shoe that incorporates a three-step mechanism. Sensors in the shoe detect a sudden inversion in the foot, measure its severity, and if deemed necessary, fire off a myoelectric pulse similar to functional electrical stimulation (FES) to help the peroneal muscles resist the inversion.
“The impulse stimulates the muscle at the critical time,” Fong explained. “An ankle sprain injury often occurs within 50 milliseconds, and with our device, we can trigger the muscle in 25 milliseconds, so it can catch up with the quick inversion motion.”
Fong and his colleagues have tried the device on 15 athletes so far, and presented their findings last summer at the 2010 International Symposium of Biomechanics in Sports in Marquette, MI. The researchers reported that when subjects wore the shoes, maximum heel-tilt angle dropped from about 18° to between 9° and 13°, and maximum angular velocity decreased from 200°–250° to 140°–170°.7
A new design
For athletes who may feel a little uneasy at the prospect of interventions that entail electricity, other options have recently become available.
“Some shoes will be better than others at preventing sprains,” said David Geier, MD, an orthopedic surgeon at the University of South Carolina in Charleston. “Running shoes are designed to protect you from repetitive impact, but you could roll your ankle more easily in those than in a basketball or a soccer shoe, which are designed for cutting, pivoting sports.”
Stability and agility were central to the design of the Ektio, a basketball shoe that recently came to market along with research-based manufacturer claims that it reduces ankle sprain risk. The shoe incorporates an interior strapping system, built into the shoe wall and designed to hold the foot firmly, reducing in-shoe motion. It also features a laterally flared outsole that may help prevent severe inversion by stopping the shoe and the foot before they can roll all the way over into a sprain.
“We’ve tried to bring the foot and the shoe together as a single unit so there’s no dissociation between them when there’s an inversion stress on the shoe,” said the Ektio’s inventor, Barry Katz, MD, a radiologist in Bridgewater, NJ, and a former college basketball player who suffered from ankle sprains in his academic career.
Katz collaborated on the design with Thomas Nordstrom, MD, an orthopedic surgeon in Bridgewater; Steven Dribbon, DPM, a podiatric surgeon in Highland Park, NJ; and an independent shoe designer named Omar Bailey. The shoe features one strap that crosses the ankle mortise and holds the heel back in the shoe; another crosses the anterior talofibular ligaments and runs parallel
to the calcaneofibular ligaments, providing support similar to that of figure-8 taping.
“The shoe allows maximum mobility in the five directions you need to play basketball—plantar flexion, dorsiflexion, internal and external rotation, and eversion,” he said. “We only stop inversion, which is the one motion you want to stop.”
The clinical community remains politely skeptical.
“I like that they’ve done some laboratory experiments, but until they actually monitor risk during sports participation, there’s no evidence to suggest that the shoe actually reduces sprains,” said Jay Hertel, PhD, ATC, director of the graduate programs in athletic training and sports medicine at the University of Virginia.
Hertel acknowledged, however, that the lateral flare design of the sole may be promising.
“Biomechanically, that makes some sense,” he said.
Ektio commissioned research (currently unpublished) from reputable labs that told LER they have no financial interest in the company. Howard Hillstrom, for one, conducted studies of the Ektio at the Hospital for Special Surgery.
“We were interested in this at HSS because we have a large orthopedic medical group; of our ninety orthopedic surgeons, at least twenty-seven are sports medicine doctors who are very involved with professional teams in the New York area,” he said. “So something that could potentially minimize ankle sprains was of medical interest to us.”
At HSS, five basketball players walked, ran, and did hopping maneuvers using either the Ektio shoe or a control shoe without anti-sprain technology.
“Between the lateral flange and the bracing, there was certainly the potential for this shoe to feel clumsy or less agile,” Hillstrom said, noting that shoe designers are often far better trained in design itself than in the sciences pertinent to athletes, such as biomechanics, mechanical engineering, or kinesiology.
“This kind of testing can show what’s going to happen in the real world, when you measure forces and torques and angles, and see exactly how technology is working on a person,” he continued. “In this case, it showed that the shoe’s stiffness could be increased through the integrated brace, but that there was no loss of agility. According to our data, athletes should be able to do all the tasks they would normally do in a basketball game wearing these shoes.”
Ethics considerations prevented certain tests that might have been illuminating, Hillstrom noted drily.
“We couldn’t have athletes jump from a certain height and land on an unstable surface, because even if this shoe prevented ankle sprains, the [control] wouldn’t have,” he said. “We would have been collecting lateral ligaments in a shopping bag and handing them back to the players.”
At Drexel University in Philadelphia, Sorin Siegler, PhD, a professor of mechanical engineering and biomechanics, assessed the shoe’s effect on ankle flexibility using a device that allowed his team to manipulate the foot in different directions, measure the amount of load applied, and assess how much motion was produced in a given direction. In five participants, three of whom were athletes, they found that the Ektio shoe provided increased support of roughly 20% in inversion without increased interference in any other direction.
“The most likely reason was that the straps maintained the foot in close proximity to the shoe so it couldn’t slide inside,” Siegler said.
What Katz needs now is quantitative field testing, according to Hillstrom.
“It would be best if only half the players on a team wore the shoe so they could study the relative incidence of sprains,” he said.
Katz is working on it.
“We’ve had players wearing it for two years,” he said, adding that there were no sprains until recently, when a college player with chronic instability sprained his ankle while wearing the Ektio.
“So I can’t claim that it’s a hundred percent effective,” Katz conceded. “But I hope we’ll be close to that.”
Cary Groner is a freelance writer based in the San Francisco Bay Area.
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