Flat Foot

A flat foot is one where the arch on the inner side is low or absent, so more of the sole touches the ground when you stand. It is one of the commonest things people worry about in their own feet and their children's, and most of the time there is nothing to treat: a flexible, painless flat foot is a normal variation in shape, not a condition. What matters is whether the foot hurts, whether it is stiff, and whether its shape is changing. This page explains how those questions are answered, for children and for adults, and what is done when the answer is yes.

Flexible and rigid flat feet

• Flexible flat foot — the arch appears when you stand on tiptoe or hang the foot off the edge of a step, and disappears again when you stand flat. This is the common type. It is usually lifelong, often runs in families, and frequently causes no symptoms at all.

• Rigid flat foot — the arch does not appear in any position and the foot is stiff. This is much less common and more likely to have a cause: arthritis, an old injury, or an abnormal bridge of bone between two of the bones in the hindfoot that has been there since childhood.

The single heel-rise test tells them apart, and is also the first sign of a tendon problem in adults: if you cannot rise onto the toes of one foot while the other is off the ground, or the heel does not swing inwards when you do, something is not working.

Flat feet in children

Almost all toddlers have flat feet. The arch develops as the ligaments tighten and the muscles strengthen, and in most children it is there by the age of eight to ten. Flexible flat feet that do not hurt need no treatment and no orthotics; there is no evidence that insoles change the eventual shape of the foot.

A child's flat foot is worth assessing when it is painful, when it is stiff, when only one side is affected, when the child is tiring or avoiding activity, or when the arch was present and has now dropped. The important condition to find in older children and teenagers is a tarsal coalition — a bar of bone or cartilage joining two bones in the back of the foot, which makes the foot stiff and painful from around the age of ten to fourteen as the bar hardens. It is diagnosed on X-ray and CT, and it is treatable.

Flat feet that develop in adulthood

An arch that flattens over time in an adult — particularly on one side, and particularly with pain on the inner ankle — is a different problem from a foot that has always been flat. The commonest cause is failure of the tibialis posterior tendon, which runs behind the inner ankle bone and holds up the arch; as it stretches and weakens, the arch collapses and the heel drifts outwards. This has its own page: tibialis posterior dysfunction. Arthritis in the middle of the foot, an old injury to the midfoot, inflammatory arthritis and, occasionally, a nerve or muscle disorder can do the same.

A foot that is changing shape should be seen sooner rather than later. While the deformity is still flexible the options are wider and the surgery smaller; once the foot stiffens and the joints wear, fusion becomes more likely.

One situation is urgent: a foot that becomes warm, swollen and flatter over days or weeks in someone with diabetes and reduced feeling in the feet can be a Charcot foot, where the bones are breaking down, and needs same-week assessment.

Symptoms

• aching along the inner arch or inner ankle, worse after prolonged standing or walking

• feet and legs that tire more quickly than they should

• the arch lowering, or the heel drifting outwards when seen from behind

• uneven shoe wear, or shoes that have become uncomfortable

• pain on the outer side of the ankle in more advanced cases, as the heel drifts and the outer side is compressed

• in a rigid foot, stiffness and repeated ankle sprains

How it is assessed

Much of the assessment is done standing and walking: the shape of the arch, the position of the heel from behind, how many toes are visible on the outer side, and the single heel-rise test. The flexibility of the joints, the strength of the tendon, the tightness of the calf and the alignment of the whole leg are checked. Weightbearing X-rays show the alignment of the bones and any arthritis. An MRI shows the state of the tibialis posterior tendon and the ligaments beneath the arch, and a CT is the test for a suspected coalition.

Treatment

Most flat feet need nothing at all. Where a foot is symptomatic, non-surgical treatment is the first step and controls symptoms for many people:

• supportive footwear with a firm heel counter and some arch support

• an orthotic to support the arch — off-the-shelf for a flexible foot, custom where the shape is unusual or the deformity more advanced

• physiotherapy to strengthen the tibialis posterior and the small muscles of the foot, and to stretch a tight calf

• a brace that controls the ankle and hindfoot, in more advanced adult cases

• activity modification, and weight management where it is relevant

Surgery is considered where the foot is painful, the deformity is progressing, and these measures no longer control it. In adults it is a reconstruction planned for the individual foot — realigning the heel bone, transferring a tendon to replace the failed one, lengthening a tight calf, and fusing specific joints only where they are already worn or the deformity is fixed. This is described on the flat foot reconstruction page. In teenagers with a coalition, the bar can be removed and the joint freed while the foot is still flexible; where it has already caused arthritis, a fusion is the more reliable option.

Dr Janan's approach

Dr Janan Chandrananth is a foot and ankle orthopaedic surgeon who completed fellowship training in Bristol and in Tokyo, the latter under a past president of the Japanese Society for Surgery of the Foot, where joint-preserving and reconstructive techniques are a particular focus. He also spent six months of paediatric orthopaedic training at the Shriners Hospital for Children in Portland during his orthopaedic training, and sees children as well as adults.

The great majority of flat feet he sees do not need an operation. Where assessment earns its keep is in the painful foot, the stiff foot and the foot whose shape is changing — and in telling those apart from the many that are simply flat.