June 2012

Minimizing the effects of knee brace migration

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Too many knee braces just won’t stay put, which can affect compliance and possibly even device effectiveness. Research on the topic is scarce, but experts say the key to minimiz­ing knee brace migration is making sure the device fits the patient’s anatomy as closely as possible.

By Shalmali Pal

Many professional athletes rely on good luck charms for game-day success. These personal talismans can range from jewelry to a favorite meal to a “blessed” pair of shorts or socks (unwashed, of course). But rarely does an athlete sit down on a locker room bench and don his lucky knee orthosis before a big game.

One could argue that knee braces do come with an element of good fortune, whether that involves prophylactically protecting the knee from injury, reducing the risk of recurrent injury, or facilitating postoperative healing. But practitioners say the reality is that most athletes, regardless of the benefits of a brace, see it as a burden rather than a blessing.

“When I was a team physician…[knee brace] compliance during the game depended on the score,” explained Jonathan Chang, MD, an orthopedic surgeon with Orthopedic Surgery & Sports Medical Group in Monterey Park, CA. “So if a team was not doing well, the players would look for any excuse and, often times, the brace became the scapegoat. It was blamed for slowing the player down and subsequently slowing the team down.”

The main complaint with knee braces? Migration.

A 1998 study in the Journal of Sports Rehabilitation on func­tional knee brace migration found that under exercise conditions, braces can migrate anywhere from 0.25 mm to 11 mm.1 And although brace technology has made tremendous strides—now featuring lighter, stronger materials and strapping that allows for instant customization—migration still can prove annoying, uncomfortable, and possibly even render the brace less effective. For athletes in particular, the perception that brace migration hinders performance may fuel their concerns that device wear could potentially reduce their speed and agility.

Lower Extremity Review spoke with a trio of experts on the prevalence and consequences of brace migration, along with solutions they’ve devised to keep a brace on a player and the player in the game.

Heading south

Photo courtesy of Allard USA.

The experts agreed that distal migration is the main problem with knee orthoses, whatever their intended use–offloading braces, prophylactic braces, or postoperative braces.

“In general, the brace tends to migrate south; it goes down the leg due to gravity,” said Barton Anderson, MS, ATC, AT, assistant professor and clinical education coordinator in the athletic training program at A.T. Still University in Mesa, AZ.

Migration in the opposite direction is less likely.

“For virtually everybody, the thigh is a lot larger than the lower leg so the likelihood of the brace migrating proximally would be very low,” Chang added.

The same holds true for rotation—possible but pretty rare. That kind of rotation also means that the orthosis is most likely migrating distally and proximally as well, explained Michael Carroll, CO, of the Hanger Clinic in Oklahoma City, OK.

While brace migration is unpleasant, does it cause biomechan­ical problems? Definitely.

“Typically, when we are providing a knee orthosis to a patient, it’s because they have a knee that’s in need of support,” Carroll said. “If this support is being supplied incorrectly by the knee orthosis, the patient doesn’t benefit from the device. The brace needs to provide adequate control in order to provide the right support.”

Chang put it quite simply: “If the brace doesn’t stay where it should, it certainly can’t protect the knee.”

Brace yourself

The key to getting that knee brace to stay in place and offer the right support is a close fit between the device and the patient’s anatomy.

For Carroll, a polycentric knee joint is the best option for lining the brace up with the anatomic center of the knee. What he particularly likes about a polycentric joint, which rotates on two axes rather than one, is that it allows for some degree of error.

“Even if the mechanical knee joint center is slightly misplaced while the brace is being donned, the device can tolerate this misalignment without requiring the orthosis be taken off and donned again,” he said. “The mechanical knee joint is able to adapt and align itself with the anatomical knee joint.”

Anderson said he likes to see the brace hinge aligned with the center of the axis of rotation of the tibiofemoral joint. He also stressed the importance of taking the brace wearer through the application process, multiple times if necessary, so that the patient knows how to correctly align the hinge of the brace with the knee.

“So when the knee bends, the brace bends. Most brace manufacturers will publish a specific application process that walks you through, step-by-step, how to get a fit that prevents migration, even during that initial application,” he said.

Responsibility for minimizing migration doesn’t stop with the first fitting session, Chang said.

“At any given time, the circumference of the thigh will differ on a day-to-day basis based on multiple variables: if a person ate a salty meal, if someone did an intense workout, things of that nature,” he said. “So the brace that fit well in the morning may not fit as well a couple of hours later after activity. The player has to have the ability to make minor adjustments to make sure the brace fits well throughout the day.”

Finally, high-performance athletes must contend with consider­able sweating and water loss, which in combination serve as the perfect conduit for migration. The combination of lubrication and changes in body measurements means that the brace will need to be adjusted by the wearer more than once, Chang added.

Performance anxiety

While migration poses a challenge for all athletes wearing knee braces, the extent of how troublesome that slippage is depends on multiple factors. First, it varies according to sport.

For example, an athlete recovering from an anterior cruciate ligament (ACL) reconstruction may be able to skip the brace altogether for a “straight-ahead activity” such as distance running, but basketball or football skills are a different story, Chang said.

“For a player who has to do a lot of cutting and explosive take-off–basketball, football, volleyball, soccer–if the brace isn’t properly in place, those first steps are a lot slower,” he said.

Photo courtesy of Townsend Design.

Despite what might seem to be a clear association between brace migration and brace effectiveness, the prevalence of migration has not typically been reported in studies investigating the effects of knee braces on athletic performance. A 2000 study in the American Journal of Sports Medicine evaluated the effects of prophylactic knee braces on college football players’ speed and agility and found that two of six braces were not associated with changes in speed and five of six were not associated with changes in agility.2 The authors of that study did note that they could not rule out whether brace migration might affect performance.

In fact, even without controlling for migration, a number of studies suggest that the presence of a brace was not necessarily a limiting factor with regard to performance beyond an initial adjustment period (see “Functional knee bracing and athletic performance”).

Even if performance measures are not affected, some evidence indicates that brace migration could alter gait mechanics. A 1989 study from the Massachusetts Institute of Technology found that an offset of more than 12 mm between the axis of the knee and the brace’s axis of rotation led to significant increases in forces and moments at the location of the hinge.3 Anterior misalignment was associated with the greatest forces and posterior misalignment the lowest.

A 2008 Canadian study,4 however, suggests that the biomechanical effects of brace misalignment may be relatively minor. Researchers from the University of Waterloo in Ontario tested properly aligned and intentionally misaligned shell and sleeve braces in 10 healthy participants during two walking exercises. Misaligned braces were positioned 2 cm distal to the optimal position.

The researchers found that an aligned shell brace reduced peak ankle plantar flexor moment compared to an unbraced condition, while both the shell and the sleeve decreased peak knee flexion angle. The aligned shell brace also increased peak knee adduction and reduced peak knee internal rotation compared to no brace. However, peak joint moments and kinematic patterns did not differ significantly between the aligned and misaligned braces. This led the authors to conclude that distal brace misalignment is unlikely to increase injury risk.

But for many athletes, negative perceptions about the value of the brace may trump any scientific evidence. For Chang, resistance to a brace is an issue of mind over matter, so compliance efforts need to be adjusted to the noncompliant athlete’s particular concerns.

“Brace companies are not going to put out a product unless it’s been tested on athletes,” he said. “The approach to compliance has to be individualized…the player is most likely looking for any excuse for poor performance. You really have to make it clear why you think this brace is important and stick to your guns on that.”

Anderson said he makes it a point to explain to the athlete that the brace will affect performance–at first. The first two to three weeks, in which the player grows accustomed to the brace and learns how to adjust it for minimum migration, are crucial.

“There is going to be this period of adaptation and adjustment,” he said. “That’s the time when I’ll hear a lot of complaints and, from a compliance standpoint, that’s likely the point where people are tempted to give up on the brace.”

What needs to be clear is that playing differently is not the same as playing poorly. Anderson recommends that a player wear the brace during daily living activities to fast-forward the accommo­dation process. During practice, Anderson strives to make the athlete understand that it will take a few practice sessions before they feel comfortable in the brace.

“That puts them in the mindset of, ‘If I give this some time, it’s going to get better.’ You don’t see as much perceived loss of performance,” he said.

Finally, there needs to be an open line of communication between the athlete and the trainer or other healthcare profes­sionals with regard to the purpose of the brace and how to achieve the best fit. Carroll recalled an instance where he initially fit a knee orthosis on a female soccer player based on information from the patient and the physician. But the patient complained of knee discomfort while pivoting because of a resulting strain to the ACL.

“After speaking with the patient’s trainer, I obtained a new perspective and valuable insight that led me to make major revisions to the patient’s orthosis. I created custom molded shells that…increased skeletal stability by preventing the opposing motion between the femur and tibia, allowing her ACL to heal,” he said. “It’s important to be somewhat accommodating when working with this patient population. The extra time and attention can make a significant difference in patient compliance and outcomes.”

Practice versus play

The experts agreed that brace migration is inevitable but not unmanageable. It’s a given that the brace will migrate to some extent, and that the player will have to adjust it throughout the course of play.

But a point of contention between athletes and practitioners is whether the brace should be worn at all times. An athlete’s concerns about how brace migration affects performance, or the need to periodically adjust a wayward brace, are potential distractions that may be more acceptable during practice than during competition. So is just wearing a brace during practice an effective compromise?

Carroll believes that postoperative braces are best worn at all times. During a game, the forces exerted on a patient’s anatomy are much more intense compared with practice. Athletes are more likely to sustain an injury courtesy of their competition than their own teammates, he said.

“As orthotists, we like to say, ‘Something is better than nothing.’ We may think, ‘stability with a little function’ while the athlete may be more concerned with ‘function with a bit of stability,’” Carroll said.

Solutions to encourage compliance by finding a balance between stability and function include integrating straps at a primary point of suspension to the popliteal area or the proximal end of the patient’s gastrocnemius, or adding supracondylar pads right above the femoral condyles to maintain suspension, he said.

Of course, the athlete has to be taught how to adjust these straps during time-outs or breaks in order to minimize migration, he said.

For Anderson, bracing for practice versus play depends on the purpose of the brace. He does not recommend that an athlete with a healthy knee wear a prophylactic brace during games.

“My experience has been that what’s more important than the [prophylactic] brace is identifying the risk factors that predispose someone to potential injury, like muscle strength, neuromuscular control, flexibility, mobility,” he said.

However, a post-ACL rehabilitation brace during a game is not out of the question. In these cases, the athlete may have gone through rehab with flying colors and is cleared to play, but the physician still recommends a postoperative brace for six months to a year.

“I wouldn’t say that I’m opposed to that,” Anderson said. “But I’d rather address the neuromuscular control factors.”

For Chang, practices take place more frequently and last longer than the game itself so the knee may be more vulnerable during the former. But play-versus-practice knee bracing needs to be decided on a case-by-case basis.

“For a player where it’s questionable as to whether he should be playing at all, the brace is going to be very important,” he said. “For others, the brace may not be as crucial. I think it’s very important for the healthcare professionals to communicate to the trainers the degree of necessity for that brace for that particular player.”

And for some players, knee brace migration is a small price to pay for peace of mind.

“I’ve had patients tell me that they felt more comfortable with the brace on. Players remember how they got hurt so there’s a certain fear factor about coming back to competition. Some of my players, they were as solid as rock and had regained motion, function, agility, but they still wanted the brace,” Chang said. “I wouldn’t go so far to call it a ‘lucky charm,’ but they understood that the brace was there to prevent further injury.”

Shalmali Pal is a freelance writer based in Tucson, AZ.

REFERENCES
  1. Brownstein B. Migration and design characteristics of functional knee braces. J Sports Rehabil 1998;7(1):33-43.
  1. Greene DL, Hamson KR, Bay RC, Bryce CD. Effects of protective knee bracing on speed and agility. Am J Sports Med 2000;28(4):453-459.
  1. Regalbuto MA, Rovick JS, Walker PS. The forces in a knee brace as a function of hinge design and placement. Am J Sports Med 1989;17(4):535-543.
  1. Singer JC, Lamontagne M. The effect of functional knee brace design and hinge misalignment on lower limb joint mechanics. Clin Biomech 2008;23(1):52-59.
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