Help for Faulty Foot Mechanics
Lloyd Nesbitt, DPM
THE PHYSICIAN AND SPORTSMEDICINE - VOL 27 - NO. 5 - MAY 1999
Foot pronation—inward tilting of the ankles and flattening of the arches—is a normal part of walking and running. But when it's excessive, it can lead to foot, ankle, or even knee pain. Properly designed shoe inserts, called orthoses, can help correct overpronation.
The Mechanics of Pronation
Excessive pronation (figure 1) does not necessarily mean having "flat feet." Even though people's arches may be relatively high when they lie down or sit, there can be overpronation when they stand.
A certain amount of pronation is normal. During the walking or running stride (or "gait cycle"), the heel strikes the ground and the foot rolls inward to absorb shock and adapt to the surface. This is particularly important if the surface is uneven.
Just before the foot pushes off, it should become a rigid lever as the arch rises and the ankle straightens. If instead the arch remains flattened and the ankle stays tilted inward, muscles and tendons will be stressed and the foot will undergo excessive wear and tear.
Overpronation can contribute to other painful conditions of the foot, leg, and knee, including overstretching of the band that extends from the heel to the ball of the foot (plantar fasciitis), enlarged toe joints (bunions), pinching of nerves in the forefoot (Morton's neuroma), calluses, runner's knee (patellofemoral syndrome), and "shin splints."
Pronated foot structure is often inherited. Before children reach the age of 3 or 4, however, it is normal for their feet to appear fairly flat because of a fat pad under the arch. After that age, the fat pad should be outgrown and the feet should be stable; only then does inward tilting of the foot and ankle bones become evident.
If left untreated, overpronation can cause problems that persist into adulthood. Regardless of a person's age, correcting foot mechanics can help relieve pain.
Doctors often recommend premade wedges, arch "cookies," or similar shoe modifications to correct excessive pronation. Arch supports that are available in drugstores and sporting goods stores may reduce excessive pronation to a degree and provide enough support or temporary comfort to be helpful for some patients. And soft-soled, lace-up walking shoes or good running shoes made for pronated feet may help symptoms of overpronation. Sometimes, though, off-the-shelf devices or shoes are not specific enough to precisely control overpronation, and custom orthoses (sometimes called "orthotics") are needed.
Custom orthoses (figure 2) are available from various sources and are designed with varying degrees of precision. They may be prescribed by podiatrists, orthopedists, family doctors, and other healthcare providers. Some providers use a simple tracing or imprint of your foot to measure for orthoses that are similar to off-the-shelf inserts. A more precise orthotic insert is made using a plaster impression of the foot.
Foam impressions. Orthoses are often fitted or formed by having you step into a box containing a special foam that is easily compressed. This is quick, easy, and nonmessy. A disadvantage is that the process often captures a pronated rather than corrected impression of the feet; hence foot mechanics and gait may not be corrected. Also, these orthoses may be made or modified from a standard orthosis and not precisely customized to your foot.
Computer analysis. Some newer orthotic devices are made after a computer assessment of gait and foot function. With this method, you walk on a pad, and a digitized readout of your foot pressure is displayed on a monitor. The computer, in most cases, is not actually used to make the device, but only to capture the impression of the foot. These devices usually are not custom made, and so the correction of foot mechanics may be limited.
Plaster casts. Orthoses can also be molded from plaster casts of the feet in their corrected position. The casts are used in a laboratory to fabricate orthoses that precisely control the mechanics of your walking cycle.
While plaster casting is probably the most accurate and effective method, it is also the most expensive. You and your healthcare provider will need to work together to decide which type of orthosis is best for you.
Future trends. In the future, prescription orthoses may be made by computerized three-dimensional scanning. The data would be sent by modem to the orthotics lab and used to create three-dimensional models, which would then be used to create the orthoses.
Make Tracks for Treatment
If you are having problems with your feet, legs, or knees that may be related to your foot structure, it's important to see a physician or podiatrist for a thorough evaluation. If you find out that your feet overpronate, orthoses that provide proper foot correction could help keep you moving freely for many years to come.
Remember: This information is not intended as a substitute for medical treatment. Before starting an exercise program, consult a physician.
Dr Nesbitt is a podiatrist in private practice in Toronto.