September 2017

Soft braces: Experts hunt for potential mechanisms

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Soft braces are not designed to change lower extremity alignment or joint forces, but research suggests they may influence knee and ankle biomechanics in other ways, including by enhancing proprioception. This line of investigation could open the door to new therapeutic opportunities.

By Stephanie Kramer

Soft braces are widely used at the knee and ankle for relieving pain and preventing injury. Although they do not address joint issues mechanically, the number of studies documenting their association with pain relief is growing, and researchers are also inching toward an understanding of the underlying mechanisms responsible for such effects.

“We take soft braces for granted,” said Nerrolyn Ramstrand, PhD, BP&O, an associate professor of prosthetics and orthotics at Jönköping University in Sweden. “A soft brace is a quick solution that we can offer patients. They’re relatively simple, but we don’t know enough about the underlying mechanisms that are facilitating function.”

Soft bracing is a common approach for management of knee osteoarthritis (OA), patellofemoral pain (PFP), and the chronic ankle instability that can lead to ankle osteoarthritis, so it’s an important issue.1-4

In one oft-cited study in support of soft bracing, researchers from the University of Southern California (USC) in Los Angeles found a soft brace was associated with increased patellofemoral joint contact area as well as with decreased pain in women with PFP, despite having no effect on patellar alignment.5

Patients who feel a rigid brace is too bulky and uncomfortable may be more willing to wear a softer one, but even a soft brace can be difficult to apply and fit correctly.

“People have shown soft braces do reduce pain. The question is what is the mechanism?” said first author Christopher Powers, PT, PhD, director of the Program in Biokinesiology and codirector of the Musculoskeletal Biomechanics Research Lab at USC.

An intriguing possibility to emerge from current research and clinical discussions is that soft braces, which are not designed to change alignment or joint forces, may influence biomechanics in other ways, including by enhancing proprioception. This line of investigation could open the door to new therapeutic opportunities.

Potential mechanisms

As reported in this magazine in June, researchers presented new findings on soft braces at the 2017 International Society for Prosthetics and Orthotics (ISPO) World Congress in Cape Town, South Africa (see “Sleeves showcase softer side of knee pain management,” June, page 30).

In one study, researchers at the University of Central Lancashire in Preston, UK, evaluated four people with mild to moderate knee OA and 10 controls during a step-down task, with or without bracing.6 In both groups, bracing led to biomechanical changes, including a significant reduction in transverse plane range of motion. Knee OA patients also reported improvement on the Knee Injury and Osteoarthritis Outcome Score (KOOS).

“If you have improvements in knee movement, particularly in the transverse plane, there will be improved stability and the patient’s symptoms will improve,” said James Richards, PhD, a professor of biomechanics at the university, who presented the findings. “A soft brace makes the knee more stable, possibly not through mechanical effects, but through proprioceptive effects.”

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A recent paper in the Archives of Physical Medicine and Rehab­ilitation supports these findings.3 The meta-analysis of 11 studies on knee OA patients concluded soft bracing improved symptoms and joint functioning. The review authors speculated that knee sleeves may enhance proprioception by stimulating skin mechano­receptors, leading to improved muscle activity. Theoretically, this could decrease loading and improve knee joint stability. Other potential mechanisms include better biomechanical balance7 or lower joint contact forces due to reduced cocontraction of the muscles.8,9

“We found that wearing a soft brace can improve pain in the immediate term and improve physical function in the long term,” said study leader Tomasz Cudejko, a PhD fellow at VU University Medical Center Amsterdam in the Netherlands. “This is contradictory to the belief that a brace is a temporary treatment measure.”

In the USC study mentioned earlier,5 Powers and colleagues used axial magnetic resonance imaging (MRI) to assess changes to joint contact area and patellar displacement during 0°, 20°, 40°, and 60° of knee flexion with or without a brace. The authors concluded increased joint contact area, not improved tracking, was associated with reduced pain.

“A lot of research on soft braces shows that neoprene braces don’t affect tracking per se.10,11 Their influence is more subtle,” Powers said. “They don’t control how the patella tracks. That’s the myth. We think it’s more that it’s a compressive effect.”

A 2010 study suggests wearing a knee sleeve may influence brain activity. Using functional MRI, scientists demonstrated altered activity in the sensorimotor cortex in 13 female volunteers during knee flexion and extension while wearing a knee sleeve, compared with no sleeve.12

Soft braces and subgroups

A clearer understanding of what soft braces can achieve—and what makes them effective—is crucial for determining which subgroups of patients may be helped by a softer approach, Richards said.

“Knee bracing may not work on all patients all the time,” he said.

The key is to identify which patients may benefit, Richards said. For example, one subgroup of patients with knee OA are those who develop an accelerated form of the disease (see “The clinical implications of accelerated knee OA,” April 2016, page 43). Richards and colleagues have been developing a detailed classification system for subgroups of patients with PFP,13 which they described in the January issue of LER (see “Patellofemoral pain subgroups: A critical first step toward personalized clinical intervention,” January, page 18).

At the ISPO Congress, Richards presented a paper on soft bracing for one of the three PFP subgroups his team has identified.14 The 20 recreational athletes with PFP in that study were all members of the “strong” subgroup, meaning they did not have weakness in the hip abductors or quadriceps muscles. The researchers found wearing a soft brace during run-and-cut movements was associated with significantly decreased peak patellofemoral forces, patello­femoral pressure, and loading rate, along with improved pain, compared with no brace.

Proprioception

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As with the Central Lancashire group’s findings in patients with knee OA, Richards believes soft bracing in patients with PFP also has proprioceptive effects, which—at least in one subgroup—may also improve stability and functional performance as well as pain.

“There were hand-in-hand changes. Patients experienced improvements in both knee stability and KOOS scores,” Richards said. “Improvements in movement control can lead to improvements in stability, and this in turn can improve symptoms and people’s ability to play sports.”

Similarly, a Belgian study published in the Clinical Journal of Sports Medicine in 2008 explored the proprioceptive effects of a neoprene knee sleeve in military recruits, about 30% of whom have been previously reported to develop PFP after six weeks of basic training.15

Sixty-four healthy adults underwent four consecutive tests of active joint repositioning before and after a fatigue protocol and with or without a knee sleeve on one limb. The authors found joint repositioning was more accurate acutely after application of the knee sleeve than with no sleeve; after the fatigue protocol, positioning errors increased in the control limb but were similar to prefatigue error levels in the braced limb. After the knee sleeve was removed postfatigue, error levels were similar in both limbs.

“It’s probably not a mechanical effect, but a neurophysiological one,” said lead author Damien Van Tiggelen, PhD, visiting professor in the Department of Rehabilitation Sciences at Ghent University and head physical therapist at the Military Hospital Queen Astrid in Brussels. “Once you remove the brace and do a test of reposition, the effect is immediately gone.”

The Belgian findings are consistent with those of researchers from the University of Western Ontario in London, Canada,16,17 who reported small but significant improvement in joint position sense associated with the use of a neoprene knee sleeve—but, interestingly, also suggested that some individuals may experience greater proprioceptive benefit from a knee sleeve than others, which supports the subgroup theory discussed earlier.

A later randomized clinical trial from the Fowler Kennedy Sport Medicine Clinic in London, Canada, reported use of a neoprene knee sleeve after anterior cruciate ligament (ACL) reconstruction did not differ from use of a functional knee brace with regard to anterior tibial translation, the single-limb forward hop test, or Tegner Activity Scale.18

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The findings of a 2017 paper from the University of Central Lancashire19 may help explain the Canadian results. In 13 healthy male recreational athletes, a prophylactic knee sleeve was associated with significantly lower ACL loading rates during cutting and single-leg hop tests compared with no sleeve; however, loading rates did not differ between the two conditions during running.

“The prophylactic knee sleeve significantly reduced the rate at which the ACL experienced loading during the more dynamic cut-and-hop movements,” said lead author Jonathan Sinclair, PhD, an associate lecturer at the School of Sport and Wellbeing at the University of Central Lancashire.

Anecdotally, soft braces also can be associated with improved proprioception at the ankle, Ramstrand said.

“People who have had ankle problems and thus decreased proprioception sometimes use a soft brace as a prophylactic measure,” she said. “It may help reduce the incidence of ankle sprains.”

Soft brace design

A current line of investigation related to the potential benefits of soft bracing involves the extent to which brace design may play a role.

One hypothesis is that the amount of pressure a knee brace applies affects proprioception.

In a paper presented at the ISPO Congress, Ramstrand and colleagues compared the effects of two braces in 20 healthy men and women.20 Participants wore either a neoprene sleeve or a brace with rigid joints. The researchers found that, though the rigid brace applied greater pressure than the sleeve, more rigid bracing was also associated with a poorer sense of passive motion.

“If you apply large amounts of pressure—a stiffer orthosis with maximum flexion—in healthy individuals, proprioception decreases. This suggests there is a threshold,” Ramstrand said. “The flipside is there is no orthosis on the market that addresses that.”

Although it was a significant finding, these were test conditions and may not apply to normal walking, she added.

Other research presented in Cape Town suggested the tightness of a soft brace had no significant influence on pain or function in 44 patients with knee OA. Cudejko and colleagues reported no difference between a properly fitted soft brace and a looser one with regard to pain, activity limitations, or knee confidence during perturbed treadmill walking.21

According to Ramstrand, the effectiveness of soft bracing may involve a combination of factors, including the material’s rigidity, its effects against the skin, and pressure.

“Even a Band-Aid can affect skin stretching,” she said. “If [the sleeve material] is stiffer and there is more pressure, then the stretching of the skin is also greater.”

The type of interface material used—silicone versus gel, for example—may also make a difference, Ramstrand said.

“The design of the knee brace is important, but no one has looked at that,” she said.

Similarly, Richards said brace characteristics could contribute to improved pain and function, partly by activating receptors in the skin.

“The skin sensation sends information to the sensory part of the brain, and the motor cortex sends signals to the muscles which control the biomechanics at the joint,” he said. For example, the use of 3D knitting could produce different tensions over the patella, influencing proprioception.

However, Van Tiggelen suggested that specific design features may not be critical.

“I think it’s just the wrapping and compression on the skin that’s important. It doesn’t matter if it’s elastic or neoprene,” he said, though he noted he hasn’t yet investigated the effects of different braces on proprioception.

Other practical issues for clinicians include whether the effects of soft bracing are time-limited.

“Is it an immediate effect? Or is it long-lasting? We don’t know the answer to that yet,” Ramstrand said.

Another concern is that even a cloth brace can be a challenge to apply and fit correctly. Ramstrand noted that in their study presented in Cape Town, two assistants helped patients properly position the brace. This is important, she said, not only for healing but for maximizing compliance.

Practice pointers

Clinical decisions about bracing, experts noted, are primarily determined by the indication and the goal of treatment.

“It depends on what the clinician is trying to achieve,” Powers said. “A rigid brace would provide more structural support for the joint. It would be more effective at preventing unwanted motion. A soft brace would not affect rotation or restrict movement to any great degree.”

For example, the use of a rigid brace may make sense for short periods of time, such as in the period shortly after surgery.

“If the patient has true mechanical instability, such as after an anterior cruciate ligament repair where you want to protect the graft, a more rigid bracing would be a safer bet,” Richards said. “If you want to improve control, then soft bracing could work.”

Yet many patients may not realize they have impaired proprioception. In a second study22 on the same 64 reportedly healthy military recruits from the aforementioned Belgian study, about half had a joint position sense error of more than 5° on each side at baseline, Van Tiggelen said. In those with poor proprioception at baseline, a neoprene knee sleeve was associated with significantly improved joint position sense before and after a fatigue protocol; in those with good proprioception at baseline, the sleeve was associated with postfatigue improvement only.

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This has implications for therapy, Van Tiggelen said.

“Any patient with poor proprioception should wear a brace during training or rehabilitation,” said Van Tiggelen. “If you can identify lacking proprioception, you can add a tool that is immediately helpful to them.”

Athletes who fear reinjury, as well as older patients, may feel more confident with knee or ankle bracing, Ramstrand said.

“A soft brace can give balance confidence in elderly people,” she said, adding that clinicians should ask patients what it is they want to do and whether they are able to do it.

Yet adherence with any type of bracing can be an issue in clinical practice.

“Patient compliance can be really low,” Van Tiggelen said. “Clients are absolutely not motivated to wear a brace.”

However, many patients who don’t want to wear a rigid brace because it’s bulky and uncomfortable may be more willing to wear a softer one.

“Soft braces are relatively comfortable and are easier to put on, especially for elderly patients,” Ramstrand said. “They cost less, too. And people can buy them at a sports shop—they don’t need to see a clinician.”

Athletes are often worried that wearing a brace could weaken their muscles; Van Tiggelen said such concerns are misplaced, but also noted patients should avoid relying on a brace if possible.

“You can also improve proprioception by training,” he said. “The brace is just a helpful tool.”

Powers also cautioned against using as a brace as long-term measure.

“They don’t necessarily fix what’s causing the pain,” he said. “When the brace comes off you haven’t fixed anything.”

Stephanie Kramer is a freelance medical writer based in Berlin, Germany.

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