Left foot with a moderately low arch

Pes Planus (Flat Feet)

What is it?

Pes planus or flat feet is when the arch on the inside of the foot is lower than what would be considered normal. This may be worse on one foot compared to the other. Pes planus (flat feet) can be mild, moderate, or severe.

What will I see and feel?

Imprint of flat feet
Figure 1: Flat feet imprint

Mild and moderate pes planus (flat feet) is harder to see as the arch is lower than normal, but not completely flat on the ground. When looking from the side, the arch may only be one or two centimeters from the ground. This is not an exact measurement, but may give an idea about what to look for. When standing, the inside of the ankle may turn inwards.

With severe pes planus (flat feet), the arch is completely flat on the ground and the arch is not visible from the inside of the foot. When walking on the beach or with wet feet, the foot leaves an impression without any gaps on the inside of the foot (see Figure 1). A bone on the inside of the foot may bulge out to the side. This bone may rub against the ground or the side of the shoe causing redness, pain, and/or callusing.


By age six, the arch has developed. Prior to this age, it is normal to see kids with flat feet. Once their arch has developed, it is important to determine how the foot has developed to prevent and understand any pain in the future.


Pes planus (flat feet) is commonly related to genetics. If you have flat feet, it is very likely that someone on either side of the family have the same feet.


Over time, the arch may decrease. This could be due factors such as surgery, an injury, rapid weight gain (such as pregnancy), age related, or certain conditions. There are lots of structures holding the arch up. If any of these structures weaken, stretch, or move, the arch may collapse.

Why now?

You may not realize you have pes planus (flat feet) until someone tells you or pain develops. This pain may develop from a specific incident or an accumulation over time. As mentioned above, the acquired factors may cause pes planus (flat feet) later in life.

Injury or Surgery

After a major injury or surgery to the feet, they typically change because the foot is directly affected. An injury or surgery higher up, such as the knees, hips, or lower back, may not have an immediate effect to the arch height, but may change the way you are walking.


With such a rapid weight change, the feet do not have time to adapt and tend to collapse. Some notice the collapse after their first pregnancy, and some not until their second or third. A common sign of arch collapse is an increase in shoe size. This increase may be in the length or width, depending on which arch collapses.


Over time, the muscles weaken and the ligaments start to stretch. When this happens, the arch begins to collapse and change.


Certain conditions may weaken the foot and accelerate or worsen the development of pes planus (flat feet). One example of this is diabetes. A complication of diabetes is neuropathy, which may hide an injury or prevent healing leading to something called Charcot Foot. This is similar to a severe pes planus (flat feet).


Gloved hand holding up a foot orthotic to the bottom of a foot

Custom orthotics support the arch to prevent and relieve pain that is associated with flat feet. Pain may develop from overworked muscles, worn out joints, stretched ligaments, or friction from contact on the floor or shoes. Over the counter inserts are another way to support without the custom features. This may be used to prevent pain or in children growing rapidly.

Because our feet change over time, we typically recommend yearly checkups, and recasting after five years or after a major change that may affect the feet.


It is important to strengthen the feet to prevent further collapse over time. If consistent, strengthening may also increase the arch slightly. The effectiveness of strengthening depends on the severity and mobility of the feet.


If you would like more information, feel free to contact us!

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