All babies have flat feet and only about 15% of adults have flat feet. This is not changed by any intervention, such as in-soles or exercises, but is due to the natural development of the medial longitudinal arch. Indeed it has been shown in India that adults who wore shoes as children are (a little) more likely to have flat feet than adults who did not wear shoes as children. I have been unable to establish why there is such widespread concern about flat feet. After all, the presence of an arch does not indicate that the foot is normal. The child in Fig 1 for example has a severe condition of the sensory and motor nerves and the feet are stiff and painful.
It is also true that some flat feet are not normal, and it is the job of the clinician, such as a GP, physiotherapist or orthopaedic surgeon, to distinguish normal from abnormal and to give appropriate advice. This is an important distinction because an abnormal flat foot often needs treatment, whereas a normal flat foot usually just needs comfortable shoes, just like any other foot. The simplest way to tell whether a flat foot is normal is to test its flexibility. As a general rule a normal flat foot is flexible and an abnormal flat foot is stiff. When a child of any age stands on tip-toe, the arch should form (Figs 2 & 3). This does not exclude general abnormalities (the child in Fig 3 has a muscle condition) but does demonstrate that the flat foot is flexible and therefore normal.
A stiff flat foot is often uncomfortable and can even be painful. The pain can be the cause of the flat foot or a result of the flat foot. There are a few relatively common causes, such as neuromuscular disorders, tarsal coalition and inflammation (including arthritis and infection).
Occasionally a flexible flat foot is uncomfortable enough to warrant treatment, but it is important to establish further that the foot is normal even if the foot is flexible on the tip-toe test. Tightness of the calf muscles and/or genuine joint laxity are the two conditions that are often associated with a symptomatic flexible flat foot. Such feet are rarely symptomatic all the time and will respond to simple measures such as an orthotic insole with a heel raise. Most sports shoes however have a big heel and are soft and accommodating enough to provide relief. Sports shoes have come a long way in the last 20 years on the basis of a good understanding of foot (and lower limb) biomechanics.
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