Orthotics, also called shoe inserts or orthoses, are often prescribed for the treatment of flat feet and pronation related problems. The sale of in-shoe foot orthotics is a huge industry. The Canadian Medical Association Journal reported that annual sales of orthotics were projected to reach US $4.7 billion dollars a year by 2015.
Many people use orthotics with the belief that wearing them will help them prevent or recover from injuries. Despite this widespread use, there is not a lot of research supporting the benefits orthotics are often claimed to provide.
Dr. Hamill, professor of kinesiology and the director of the biomechanics laboratory at the University of Massachusetts states that:
the main thing to note is that, as biomechanists, we really do not know how orthotics work.
One issue making orthotic prescription difficult is that individuals respond differently to them. A 2003 study found that some runners that overpronate responded as expected when given orthotics to correct their foot motion.
Some of the subjects, however, showed increased rearfoot motion. This means they were pronating more than without the inserts. An insert that corrects pronation in one person may actually worsen the problem in another. The authors of the study suggested that people with flat feet may pronate more when wearing orthotics.
Dr. Benno Nigg, a professor of biomechanics and co-director of the Human Performance Lab at the University of Calgary in Alberta, has spent a good amount of time studying the way orthotics work. An article from The New York Times in 2011 discussed Dr. Nigg’s research into how unpredictable the effect of wearing orthotics can be:
Dr. Nigg sent a talented distance runner to five certified orthotics makers. Each made of a different type of insert to “correct” his pronation. The athlete wore each set of orthotics for three days and then ran 10 kilometers, about 6 miles. He liked two of the orthotics and ran faster with them than with the other three. But the construction of the two he liked was completely different.
A number of variables are involved when looking at the effects of orthotics. Not only is there a lot of variability in the way orthotics are constructed, but every individual also has a unique bone and joint structure that needs to be considered.
Prefabricated vs. Custom Orthotics
There is a lot of debate on whether custom made orthotics are better than the kind you buy off-the-shelf. Individual studies generally show no difference between the outcomes of wearing either type. There was one study that concluded that pre-fabricated (non-custom) orthotics are better at controlling foot motion while custom-made orthotics were better at shock absorption.
Comfort may also be an important factor regarding the choice of orthotics. If a person feels like they can move better when using a certain insert, then likely they’ll feel better in general.
Orthotic Model Not So Certain
The theory behind orthotic supports comes from the idea that excessive pronation of the foot causes pain and injury. Orthotics were believed to control the motion of the foot and correct skeletal alignment thereby making them capable of treating or reducing the risk of injury. A 2009 study published in the British Journal of Sports Medicine concluded from available studies that orthotics cause only a small (~2 degree) change in foot and ankle motion. So if orthotics don’t change the way the foot moves, then why do some people feel better when they wear them?
- Shock Attenuation: an orthotic acts as a cushion between the foot and the ground.
- Change in Kinetics: an orthotic device alters the way forces travel through the leg
- Neuromotor Control: an orthotic may provide sensory input to the foot that results in improved muscle function.
- Motion in Other Joints: most orthotic studies have only looked at rearfoot motion so it’s still possible orthotics have an effect by influencing the motion of other joints in the foot.
- Placebo Effect: sometimes the expectation that an intervention will work is all it takes to feel better
There is another type of shoe insert supposedly designed to help strengthen the arch. These inserts supposedly work by providing a stimulus to the sole of the foot in the area of the arch. Basically, there is a little dome that sits under the arch. The makers of these orthotics claim having that bump activates the muscles in the arch. In theory, I like this idea. Think of the way your foot moves when walking barefoot over a rough surface. You step more deliberately because you need to be careful how you transfer weight onto your foot. So I can imagine how these insoles might give some sensory feedback about the movement of your arch which could help control pronation. Whether this type of insole works in practice requires further research. Ultimately, I still feel that exercises are a better approach for improving the shape and function of the arch.
I’m not an advocate for using orthotics, generally. I had a bad experience with them in that I have a strong suspicion that they contributed to the plantar fasciitis I had in my left foot. Undoubtedly, there are people who benefit from them though.
There is no “one-size-fits-all approach” that will work for everyone, but I think there is evidence that many cases of flat feet and excessive pronation can be managed with exercise. Using an artificial arch support could conceivably prevent the arch from doing what it is built to do–which is to support the foot!
If anything I would go in the opposite direction and say many people could benefit from spending more time going barefoot rather than in supportive footwear. If flat feet are caused by weakness in the muscles that support the arch then those muscles need to be used and strengthened, not held in a fixed position.
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