March 2017

Rocker-bottom footwear: effects on balance, gait

Footwear with rocker soles are best known for helping to redistribute plantar pressures during gait in patients with diabetes, but research suggests they also have clinically relevant effects on balance and gait that can be beneficial for some populations but potentially dangerous for others.

By Greg Gargiulo

Although shoes were once used exclusively to protect the foot, they are now often used to improve the function of the feet and lower limbs as well.1 To this end, there has been an upswing of interest in various methods to modify locomotion to address specific patient needs related to load modification, rehabilitation, and injury prevention.2

Rocker bottom soles, with added thickness and other design features intended to change gait mechanics, have been used to accomplish these goals for decades, and are currently the most commonly prescribed external therapeutic shoe modification.3-6

“Next to foot orthotic devices, rocker bottom soles are the proverbial ‘aspirin’ to chronic and temporary foot problems,” said Arnie Davis, CPed, founder and owner of Davis Foot Comfort Center in San Francisco, who specializes in rocker soles. “Like foot orthotics, rocker bottoms can offer a number of mechanical remedies, such as inhibiting excessive or painful joint motion, preventing unwanted compensation for immobile joints, diffusing and reducing ground reactive forces, and aiding in the harmony of movement when weight flows through the foot during gait.”

Lower extremity clinicians may not agree on all aspects of rocker-sole utilization, but they do agree that the devices should be prescribed on a case-by-case basis.

Potential applications for shoes with rocker sole designs have become wide-ranging, and the biomechanics of how they impact gait has been well researched.1,3,7,8 Several studies also suggest rockers can be effective for managing gait issues associated with numerous conditions, including Achilles tendinopathy,9-11 knee osteo­arthritis (OA),12,13 claudication,14 hemiplegia,15,16 plantar fasciitis,17 chronic low back pain,18 first metatarsophalangeal (MTP) joint OA,19 and following ankle arthrodesis.20

But walking—and running—in rocker-soled shoes also comes with drawbacks and risks, which are primarily related to the way they alter balance. Some studies suggest rocker soles can negatively affect wearers’ balance and in some may even increase the risk for falls and injury.9,21,22

Situational instability

Intentionally interfering with balance was the core concept behind Masai Barefoot Technology (MBT) shoes, which were designed to transform flat, hard surfaces into unstable surfaces to enhance functional performance and address gait-related issues.1 MBTs and similarly designed “toning shoes” experienced a surge in popularity in the late 2000s, but several models did not live up to their claims, and attention surrounding them has waned.4,23,24

On the whole, though, the existing data have not yet reached a clear conclusion on the basic effects of rocker bottom shoes on walking performance. Although rockers appear beneficial for certain applications, the jury is still out for others, and prescribing them must therefore be done cautiously and on a case-by-case basis.8

“Rocker-sole footwear produces significant changes in lower limb biomechanics and has the potential to alter function in both a beneficial and detrimental manner,” said Hylton Menz, PhD, a senior research fellow and professor in the College of Science, Health and Engineering at La Trobe University in Melbourne, Australia. “When used appropriately, such footwear may be a useful adjunct treatment for some musculoskeletal disorders. However, rocker-sole footwear is not suitable for everyone, so their selection needs to be carefully considered.”

Biomechanical factors

Figure 1. A boot with a rocker sole. (Photo courtesy of Arnie Davis, CPed.)

Research on the therapeutic use of rocker soles dates to at least 1950,25 and a 1991 Schaff and Cavanagh study found rocker soles reduced peak plantar pressures by 30% in the medial forefoot, central forefoot, and toe regions compared with a conventional extra-depth shoe, suggesting rockers may help reduce the risk of ulceration in these foot regions.26

This can be especially beneficial for patients with diabetic peri­pheral neuropathy in danger of developing ulcers. In this context, a sole with a forefoot rocker pattern is used to functionally relocate the apex of the forefoot rocker posterior to the metatarsal heads, which reduces pressure on the met heads and promotes the transition from midstance to toe-off during gait.4,5,27,28

But reducing ulceration risk is far from the only function rocker soles can serve, and the forefoot rocker is just one of many variations in their design.

“It is important to understand that rocker shoes can be used to alter the biomechanics of walking and running in a number of different ways,” said Steve Preece, PhD, deputy director of the Centre for Health Science Research and research fellow at the University of Salford in the UK. “While in people with diabetes, the objective is to reduce plantar pressures, the aim in other patient populations will often be to reduce or alter other biomechanical parameters, such as altering joint moments or changing muscle activation patterns.”

According to Chapman et al,29 rocker soles have three key design features: apex angle, apex position, and rocker angle. By tweaking and modifying these features, a variety of designs can be created and further customized, each with its own biomechanical goal.29 In addition to the forefoot rocker—also known as the metatarsal head rocker, which Davis said is “the most common, and sort of the general rocker bottom”—other designs include the metatarsophalangeal joint rocker (or toe-only rocker), negative heel rocker, double sole rocker, Lisfranc rocker, and ankle joint rocker.3,30

“I prescribe them for patients with hallux rigidus, hallux limitus, osteoarthritis, rheumatoid arthritis, and those with an amputation from the forefoot or midfoot, among other conditions, and the beauty of the rocker sole is that you can control some of the pressures exerted on the foot by using different designs,” said Rob Sobel, CPed, past president of the Pedorthic Footcare Association and previous owner of Sobel Orthotics & Shoes in New Paltz, NY. “They are also a good idea any time someone is in an ankle foot orthosis [AFO].”

Design tradeoffs

A 2004 Brown et al study28 identified unique tradeoffs with three rocker sole designs in healthy individuals (see “For those about to rock, we caution you,” December 2009, page 18). The toe-only rocker gave the best forefoot relief but increased pressure on the midfoot, while the double rocker sole was effective for individuals with a prominent fifth metatarsal base or a rocker-bottom foot deformity, and the negative rocker functioned similarly to the toe-only rocker, but with slightly more reported stability.28

This is not the only evidence of tradeoffs in rocker-sole use.

A 2017 Sobhani et al study,9 which was associated with two earlier studies,10,11 evaluated the effect of rockers on running mechanics in endurance runners with Achilles tendinopathy. They compared a standard running shoe with a modified version of the same shoe with a stiffened rocker placed 53% proximal to the metatarsal region. They found the rockers were associated with reduced positive and negative work, as well as internal plantar flexion moment, at the ankle; however, they also were associated with increased mechanical work at the knee joint. The findings suggest this type of rocker may help to decrease the load on the Achilles tendon, but may also increase the risk of overuse injuries at the knee joint.9

“Knee load was higher when running with the rocker shoes compared with the neutral shoes, which is a warning sign people should be aware of,” said lead author Sobhan Sobhani, PT, PhD, an assistant professor of physiotherapy and research coordinator in the Faculty of Rehabilitation Sciences at Shiraz University of Medical Sciences in Iran. “We never recommended rocker shoes to be used as a permanent running shoe, and have always suggested wearing them as an adjunct load management option, especially at the beginning phase of Achilles tendon rehabilitation. We still need additional clinical trials to check the clinical efficacy of rocker shoes in the management of Achilles tendinopathy.”

Other research has shown that combining rockers with orthoses or integrating them into orthotic designs may elicit benefits, as well.

In a 2012 study by Fong et al, the combination of toe-only rock­er shoes and a custom-made foot orthosis was associated with a significantly lower visual analog scale pain score than either of the two modifications alone in patients with unilateral plantar fasciitis.17 Two separate 2016 Farmani et al studies investigated the impact of rockers on the gait of hemiplegic stroke patients, with one evaluating AFOs when paired with either a standard or rocker-soled shoe,15 and the other comparing solid AFOs to rocker AFOs.16 Both found rockers were associated with positive effects, including improved gait abilities and functional mobility and decreased energy expenditure.

In a similarly designed 2015 randomized controlled trial (RCT) Menz and colleagues compared the effectiveness of prefabricated foot orthoses to rocker shoes for first metatarsophalangeal joint OA.19

“Our trial essentially found no difference between the two interventions in regard to foot pain, as both groups improved to a similar degree,” Menz said. “Where the two interventions most differed was in relation to adherence, as many participants had difficulty incorporating rocker-sole shoes into their normal workplace attire. And though our trial suggests rockers are effective, a previous randomized trial23 did not demonstrate any benefits of them over flat-sole shoes in managing low back pain.”

Beyond fitness

Figure 2. Images illustrate different types of rockers, with fulcrum locations indicated by vertical red lines. (Images courtesy of Arnie Davis, CPed.)

The MTP OA study and the low back pain study both used MBT shoes for their rocker-sole interventions, which has become a rather common practice in the recent literature.2,8,12,13,22,31,32 MBT shoes originated in Switzerland in 1996 and debuted in North America in 2003. The shoe has a rounded sole in the anterior-posterior direction and a cushioned sensor under the heel area that creates a natural degree of instability to activate, strengthen, and condition neglected extrinsic foot muscles and provide benefits that are similar to those of barefoot locomotion (see “Unstable shoe designs: Functional implications,” March 2011, page 31).

“There have been a number of studies on unstable shoes, mostly on walking activities, and the literature suggests that they generally have similar biomechanics to heel-to-toe rocker-profile shoes,” Sobhani said. “Because of their unstable feature, they are believed to increase energy expenditure and are thus recommended as a good physical fitness and balance training tool, but the evidence is controversial.”

Although MacRae et al found MBTs were no more beneficial than flat sole shoes in affecting disability and pain in people with chronic low back pain,23 in a 2014 RCT wearing the unstable shoes for six weeks was associated with significantly decreased chronic low back pain but had no significant effect on quality of life and disability scores.18

A 2013 study conducted by Buchecker et al found that using the unstable shoes during level walking decreased mechanical demands on the lower body due to diminished joint moments and powers.31 The authors suggested this may help reduce the risk of hip and/or knee OA, but comes at the expense of less mechanical input to the biological structures of locomotion.31

Two other studies looked specifically into using MBT shoes as a potential management intervention for knee OA. Tateuchi et al found they reduced knee flexion moment during walking without increasing compensatory trunk lean,13 while Madden et al found peak knee adduction moment was lower in MBT shoes than nonrocker shoes, but still higher than during barefoot walking.12

Helping or hurting?

Despite the potential for reducing joint loads, researchers have stressed the need for additional studies on balance before recommending these shoes to older adults.

“The downside of MBTs, and indeed any rocker-sole shoe, is that some individuals may have difficulty habituating to the altered gait pattern induced by the shoe, and some will experience impaired balance. This is of particular concern for older people,” Menz said.

Figure 3. Rocker-bottom soles must consider the angle and base of gait. To be effective, fulcrums must be perpendicular to the line of progression. (Image courtesy of Arnie Davis, CPed.)

This inherent risk with rockers has been pointed out in other trials, as well. Kimel Scott et al analyzed the use of forefoot rocker bottom soles in younger and older adults, and found them to be destabilizing to both groups, but even more significantly in the older group.21 A 2009 study by Albright et al yielded similar outcomes, as rockers had a destabilizing effect on perturbed stance in young healthy adults.4

“The MBT is a fine, decent-made shoe, but my issue is that although they were fine for let’s say a twenty-something-year-old whose proprioception and balance were really good, they were a disaster for anyone with any kind of gait abnormality, like a fractured hip waiting to happen,” Sobel said.

Davis echoed this sentiment.

MBT-type shoes “force wearers to use certain muscles more than usual, which is their health therapeutic component. But do they help people with foot problems and pronation? I think it’s going to hurt them before it helps them,” he said. “So, although I know they can be beneficial for some, I generally don’t recommend MBTs or similar types of shoes as a rehab method for people with foot issues. But I do have a pedorthist friend in New York who loves them and has recommended them to many of his patients.”

Davis’ friend is Robert Schwartz, CPed, past president of the Pedorthic Footcare Association and current president and CEO of Eneslow Pedorthic Enterprise in New York, NY.

“We have been carrying them in our shops for almost twenty years and commonly recommend them for plantar fasciitis, posterior tibial tendon dysfunction, and hallux limitus and rigidus, especially for people with the right foot size and shape to find comfort in them,” Schwartz said. “Many people come back again and again, and I’ve found that they are great for improving balance, alignment, posture, and gait. I also wear them personally and have found them to be instrumental in accomplishing those goals.”

But, while clinicians may not agree on all aspects of rocker-sole utilization, they do seem to universally value the importance of evaluating each patient to determine if they are a good fit and giving them ample time to adapt to any type of rocker-soled shoe.

“I think all clinicians should do a gait evaluation on patients and look at their shoes beforehand to see where they’re putting excessive pressure so you know what you need to do to give them the maximum benefit, while also being cautious to make sure [a rocker shoe] is stable enough so they don’t fall on their face,” Sobel said. “You should also do some gait training with patients [once they are given rocker shoes] and help them get used to it before sending them on their way, because the rocker is different than what they were using before.”

Schwartz said he and his colleagues encourage patients to transition to rocker shoes slowly.

“Most people have to wear MBTs a little at a time until they gain strength and stamina, so we recommend wearing them an hour a day for the first few days and to increase gradually until they feel strong enough to wear them for a full day,” he said.

Researchers and clinicians also appear to share a common stance when it comes to determining optimal rocker-sole design.

“Individual tailoring of outsole geometry needs to be done with a specific biomechanical objective, such as reducing plantar pressure, altering joint moments, or changing muscle activation patterns,” Preece said. “Essentially, this is a process of trial and error where the clinician will use a pressure measurement system to evaluate the effects. There is no definitive algorithm that allows us to predict the effect of changing geometries, but this is something we are working towards.”

Davis, for one, incorporates personalization into his pedorthic practices.

“The way the foot functions depends on how the bones are shaped, which varies in everybody. So one-size-fits-all just doesn’t work,” he said. “What I aim for is finding that sweet spot for where the rocker helps with symptoms but the person still feels stable. There also has to be a flat spot [on the sole] so the person can stand still.”

Rocking on

Even given the evidence in support of rockers for many applica­tions,1,3,7-17,19 additional high-quality research is still needed to more thoroughly evaluate their effects on gait, balance, pain, and function to optimize recommendations and reduce the risk of tradeoffs like falls and injury.4,10,12,15,19

“Although there have been several studies examining the biomechanical effects of rocker-sole footwear, very few clinical trials have actually been conducted,” Menz said. “It would therefore be useful to quantify differences with various designs in more detail, so a biomechanical dose-response relationship can be determined, which could assist in appropriately targeting different models to individual patient needs. Until further clinical trials are performed, many of the proposed benefits of these shoes remain speculative.”

In the meantime, pedorthists like Sobel will continue prescribing and customizing rocker soles for the multitude of patients with gait abnormalities who stand to benefit from them, based in part on his own experience.

“In my opinion, rocker soles are invaluable as far as gait restoration and a necessary tool,” he said. “So it’s an easy sell.”

Greg Gargiulo is a freelance medical writer based in San Francisco.

REFERENCES
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