Flat Feet (Fallen Arches)
— Causes, Symptoms, Self-Test & Correction

What are flat feet?

Flat feet are medically known as pes planus. Many people think of them as "flat soles," but more precisely it is a collapse of the inner longitudinal arch of the foot.

The key is the heel. When the heel bone (the calcaneus) tilts inward — a motion called pronation — the arch above it follows and collapses inward, making the foot appear to roll outward. For this reason flat feet are also called pronated flatfoot.

What causes flat feet?

Flat feet rarely have a single cause. The most common contributors are:

• Congenital factors — naturally lax ligaments and joints that don't hold the arch well
• Weak intrinsic and posterior tibial muscles — reduced function of the muscles and tendons that lift the arch
• Weight gain & pregnancy — increased load gradually flattens the arch
• Poor gait habits and unsupportive shoes — footwear and walking patterns that encourage pronation
• Aging & posterior tibial tendon dysfunction (PTTD) — a leading cause of an arch collapsing later in adulthood, often on one side

Symptoms — what kind of pain do flat feet cause?

Flat feet don't stay in the foot. When the arch collapses, shock isn't absorbed and the load travels upward.

• Foot — pain along the inner arch, easy fatigue when standing or walking, plantar fasciitis
• Ankle — a sense of rolling inward, frequent sprains
• Knee — pronation rotates the shin inward, causing pain on the inner knee
• Hips & lower back — asymmetric flat feet can lead to pelvic tilt and back pain
• Outward signs — the inner heel of your shoes wears out unusually fast; viewed from behind, the heel tilts outward

Asymmetric flat feet — different on the left and right — are a particular cause of whole-body imbalance and deserve extra attention.

How to self-test for flat feet

Before a clinical exam, here are simple checks you can do at home.

1. The wet footprint test

Lightly wet your foot and press it onto paper or the floor.

• Normal arch — the inner middle is empty, so the print narrows like a band
• Flat foot — the inner side does not empty out; the whole sole prints solidly
• High arch (pes cavus) — the middle is nearly broken; only the ball and heel print

2. Check heel alignment

Stand barefoot and have someone look at your heels from behind. If the heel bone tilts outward (valgus) and the inner ankle bone bulges inward, advanced pronation and flat feet are likely.

3. The tiptoe test (flexibility check)

If the collapsed arch reappears when you rise onto your toes, you likely have flexible flatfoot. If the arch does not return and the foot stays stiff on tiptoe, it may be rigid flatfoot.

Flexible flatfoot vs. rigid flatfoot

This is the most important distinction for deciding treatment.

Can flat feet be corrected?

This is the most common question. Honestly: in adults, the hardened bone structure usually cannot be reversed without surgery. But that does not mean "nothing can be done."

There are three core goals:

1. Support — use custom orthotics to support the collapsed arch and heel axis and restore alignment.
2. Reduce pain — once aligned, the abnormal load on the plantar fascia, knees and hips drops.
3. Prevent progression — stop further collapse and retrain strength and gait habits alongside.

In particular, flexible flatfoot and growing children still have unhardened structure, so combining orthotics with exercise offers a wide margin of functional improvement.

Store-bought insoles vs. custom orthotics

Store-bought insoles are mass-produced to an average arch shape and act mainly as temporary cushioning. Custom orthotics, by contrast, are built from your own foot-pressure and alignment measurements to support the heel axis and arch by design. The difference is that they are a medical approach aimed at correcting alignment — not just adding cushioning.

What happens if you leave flat feet untreated?

Even without pain today, walking thousands of steps a day on a collapsed arch accumulates load. A common progression looks like this:

Arch collapse → plantar fasciitis → inner knee pain → pelvic tilt → lower back pain

The feet are the foundation that supports the body. When the foundation tilts, everything above it tilts too. That is why flat feet should be treated not as a "foot problem" but as a whole-body alignment issue.

Frequently Asked Questions (FAQ)

※ This content is provided for general health information and does not replace medical diagnosis or treatment. If you have pain or symptoms, please seek a professional examination and consultation.