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Flat foot : causes, symptoms and complications of this foot deformity

Table of contents


What is a flat foot ?



Flat foot in children





People with flat feet, also known as valgus flat foot, either have no arch or a very low arch.


Normally, there is a gap under the inside of the foot when a person stands, as the inside of the sole of the foot lifts slightly from the ground. In the case of flat foot, the inner sole of the foot may touch the ground. Unlike the hollow foot where the arch of the foot is excessively curved.


Flat foot only requires treatment if it causes discomfort in the foot, indicates an underlying disorder or causes discomfort elsewhere in the body. Some people can have this type of deformity without suffering from it.

In general, the choice of a flat foot shoe combined with a pair of orthopedic insoles is sufficient to relieve the pain.


What is a flat foot ?

Valgus flat foot occurs when a person has a very low or non-existent arch, which means that one or both of their feet can lie flat on the ground.


A human foot has 33 joints, which hold 26 different bones together. It also has over 100 muscles, tendons and ligaments. In the case of valgus flatfoot, there is a collapse of the medial arch.


The arch of the foot provides a spring for walking and helps to distribute the weight of the body on the feet and legs. The structure of the arches determines how a person walks. The arches must be both strong and flexible to accommodate stresses and support the whole body. The posterior tibial tendon plays a major role in this architecture.


When people have this type of foot condition, the calcaneus, the heel bone, can collapse inwards when they stand and walk. This is known as valgus, and it can also cause the toes to point outwards. This position of the foot often causes pain that can even prevent walking. Metatarsalgia can also develop with this type of foot deformity.

Flat foot


Differences between flat foot and standard foot



The most common symptom of this type of deformity is the pain it can cause in the foot. This can occur as a result of strain in the muscles and ligaments of the ankle.


Abnormal stresses on the knee and hip can lead to pain in the underlying joints. These strains are likely to occur if the ankle turns inwards and causes the foot to valgus.


The flat foot can also cause back pain that can be disabling, moreover a good shoe for back pain is often a shoe that will suit a flat foot.


The following parts of the body may be affected:

  • The ankle joint
  • The midfoot
  • The knee
  • Hip
  • The lumbar region

One or both feet may also be stiff.


Flat feet can also lead to uneven distribution of body weight and uneven or faster than usual wear of shoes, especially on one side, which can lead to further injury. This type of symptom is also found in the case of a hollow foot.

Abnormal shoe wear is often noticed by looking at the sole of the shoe and comparing the two.



Common causes of flatfoot include:

  • Genetic factors, as valgus flatfoot can be congenital and passed from parents to children
  • Weak arches
  • Sequelae of foot or ankle injury
  • Arthritis or rheumatoid arthritis
  • Posterior tibial tendon injury, dysfunction or rupture
  • Diseases of the nervous system or muscles, such as cerebral palsy, muscular dystrophy or spina bifida

Another condition that may cause flat feet is tarsal coalition. This condition causes the bones of the foot to fuse together unusually, resulting in stiff, flat feet. This condition is usually diagnosed in children.


People are more likely to develop flat feet if they suffer from obesity or diabetes, and they are also more common during pregnancy.


This type of static disorder can also develop with age and weakening of the posterior tibial tendon. If the posterior tibial tendon fails this usually leads to arch collapse.


Flat foot in children

Children can sometimes appear to have flat feet when the internal arch is still forming. There is no need to worry, as it will deepen over time and develop normally. In addition, the extra fat on a baby's foot will give the impression of a flat foot.


However, if a child has flat feet due to incorrect bone development or another condition, such as spina bifida, a doctor will need to treat the underlying cause.

This is usually seen during a clinical examination by the doctor during the child's medical follow-up.



If the patient does not experience any discomfort, there is no cause for concern.

However, any adult with the following symptoms should consult a doctor:

  • Flat feet that have only recently developed
  • Disabling pain
  • Symptoms that do not improve with a pair of orthopedic insoles or after wearing orthopedic shoes
  • Worsening of the deformity
  • Feet become stiff, heavy and with poor joint range

Most trained health professionals can diagnose this type of deformity by examining the feet and observing the person standing and walking.


A doctor will also look at the person's medical history. In some cases, they may order an X-ray, CT scan or MRI.



If flat feet are causing pain, a well-fitting orthopedic shoe can help. A very wide shoe or foam or silicone protection of the navicular bone can also provide relief.

Wearing shoes with a slightly higher than average heel can help to deepen the inner arch of the foot.



Orthopaedic shoe selection



Orthopedic insoles or foot orthotics with internal support custom designed by a podiatrist or pedorthist can relieve pressure and provide correction. However, orthopaedic insoles or shoes only treat the symptoms and the correction only works if they are worn.

An orthopedic shoe is still the best way to provide fast and effective relief.


Some bones do not develop properly during childhood, which can lead to flat feet from birth to adulthood. In these rare cases, surgery may be required to separate the fused bones.


When obesity is the cause of these deformities, weight loss can improve the symptoms.


From a surgical point of view, several techniques exist depending on the stage of the deformity. This may involve a calcaneal osteotomy or a lengthening of the Achilles tendon. Another possible surgery is a hind foot arthrodesis.

Surgical treatment should always be considered as a last resort.



Flat feet can lead to the formation of bunion, a deformity of the big toe.

People with other foot, ankle or leg problems may find that flat feet can contribute to the onset or worsening of the following symptoms:

  • Achilles tendonitis, an inflammation of the tendon that inserts at the back of the heel
  • Metatarsalgia
  • Osteoarthritis
  • Hallux valgus
  • Claw or hammer toes
  • Plantar Fasciitis (Calcaneal Spur), inflammation of the ligaments in the soles of the feet
  • Posterior tibial tendonitis
  • Wound over the navicular bone

Flat feet can affect the alignment of the body when standing, walking or running. As a result, they can increase the likelihood of developing pain in the hips, knees and ankles.






Author : Philippe Vesin - Pedorthist

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