A flat foot is a foot where the arch along the inside edge sits low or touches the ground completely when you stand. About 27% of the general population has some degree of flatfoot, with children showing the highest rates and adults the lowest (around 20%). For many people, flat feet cause no problems at all. For others, the lack of arch support leads to foot pain, alignment issues, and problems that can travel up through the knees, hips, and lower back.
How the Foot Arch Works
Your foot has two arches. The one most people think of runs along the inner edge of the foot, from the heel to the ball. This medial arch is built from a series of wedge-shaped bones stacked like a Roman arch, with the wider part of each bone on top and the narrow part below. This arrangement creates a natural keystone structure that bears your weight.
Bones alone don’t hold the arch up. A thick band of tissue on the sole of your foot, called the plantar fascia, acts like a bowstring connecting the heel to the toes. When you walk and your toes bend upward during each step, this band tightens and pulls the arch higher, a mechanism called the windlass effect. Tendons, ligaments, and muscles all work together to keep the arch stable. A flat foot develops when this system of support fails or never fully forms.
Flexible Vs. Rigid Flat Feet
Not all flat feet are the same, and the distinction matters for treatment. In a flexible flat foot, the arch is visible when you sit or stand on your toes, but it disappears the moment you put your full weight on it. This is by far the more common type and is often painless. In a rigid flat foot, no arch appears regardless of whether you’re standing, sitting, or lifting your heel. Rigid flat feet are more likely to cause pain and stiffness and typically point to a structural problem in the bones or joints.
A simple way to check at home: stand normally and look at your inner foot. Then rise onto your tiptoes. If an arch appears when you’re on your toes, you likely have the flexible type.
Why Flat Feet Develop
In children, flat feet are the norm. The arch develops most rapidly during the first six years of life. Babies and toddlers have a fat pad under the arch that makes feet look flat even when the bone structure is forming normally. By age six or seven, most children have a visible arch. If the arch hasn’t developed by around age 10, research suggests it’s unlikely to appear on its own.
In adults, flat feet can be something you’ve had since childhood or something that develops later. The most well-understood cause of adult-acquired flatfoot is dysfunction of the posterior tibial tendon, the tendon that runs along the inner ankle and supports the arch. When this tendon weakens or tears, the arch gradually collapses. But the tendon rarely fails in isolation. Ligaments that hold the arch bones in place, particularly the spring ligament complex, typically stretch and deteriorate alongside it.
Carrying extra weight accelerates the process. Elevated body weight increases the load on the arch with every step, straining the tendons and ligaments that hold it up. Obesity also tends to come with reduced physical activity and altered walking patterns, both of which can worsen foot deformities over time. Pregnancy, injuries to the foot or ankle, and conditions like rheumatoid arthritis can also contribute.
Symptoms and Where the Pain Shows Up
Many people with flat feet never experience symptoms. When pain does occur, it typically starts on the inner side of the foot and ankle, right along the path of the posterior tibial tendon. The heel and the ball of the foot are other common trouble spots. Flat feet are associated with plantar fasciitis, Achilles tendonitis, bunions, heel spurs, and shin splints.
The effects don’t always stay in the foot. When your arch collapses, your foot rolls inward excessively with each step (a motion called overpronation). This inward roll creates a twisting force that travels up the leg. Your shin bones rotate, your knees angle inward, and your pelvis can tilt or rotate in response. Over time, this chain reaction can cause knee pain, hip pain, and chronic lower back problems. If one foot is flatter than the other, the resulting leg-length difference can lead to a lateral curvature of the spine or recurring irritation in the sacroiliac joints where the spine meets the pelvis.
Long-term, the repeated microtrauma from poor structural support in the feet can contribute to disc degeneration in the spine. This is why some people with unexplained back or knee pain eventually trace the problem down to their feet.
How Flat Feet Are Diagnosed
Diagnosis typically starts with a physical exam. Your doctor will watch you stand, walk, and rise onto your toes to determine whether your flat foot is flexible or rigid. They’ll look at your shoe wear patterns (flat feet tend to wear down the inner edge of shoes faster) and check for swelling or tenderness along the inner ankle.
If imaging is needed, a standing X-ray provides the clearest picture. Two measurements matter most. The first, called Meary’s angle, measures the alignment between the bones of the midfoot and the hindfoot. In a normal foot this line is roughly straight; in a flat foot it angles beyond 10 degrees. The second, calcaneal pitch, measures how steeply the heel bone tilts. A pitch below 19 degrees is considered abnormal and confirms a low arch. These numbers help determine severity and guide treatment decisions.
Treatment Without Surgery
Most flat feet respond well to nonsurgical treatment. The goal is to reduce pain, support the arch, and prevent the condition from worsening.
- Arch supports and orthotics: Over-the-counter insoles can help with mild cases. Custom orthotics, molded to your foot, provide more targeted support and help control overpronation. They reduce the abnormal stresses that lead to plantar fasciitis, knee pain, and back problems.
- Supportive footwear: Shoes with firm heel counters and good arch support make a meaningful difference. Flat, unsupportive shoes like flip-flops and worn-out sneakers let the foot collapse further.
- Stretching and strengthening: Tight calf muscles pull the heel in ways that flatten the arch. Stretching the calves and Achilles tendon helps. Strengthening exercises for the muscles along the inner foot and ankle can improve arch support over time.
- Activity modification and rest: If your flat feet are newly painful, reducing high-impact activities and using ice can help manage inflammation while other treatments take effect.
- Bracing: For more severe cases, an ankle brace can stabilize the foot and reduce strain on the posterior tibial tendon.
When Surgery Becomes an Option
Surgery is reserved for people who have tried nonsurgical approaches without adequate relief. There’s no single flat foot surgery. Instead, surgeons choose from a menu of procedures based on the severity and flexibility of the deformity.
For flexible flat feet that still have some correction potential, common procedures include shifting the heel bone back into alignment under the leg (calcaneal osteotomy), lengthening a tight Achilles tendon, and transferring a nearby tendon to take over for the weakened posterior tibial tendon. If the ligaments that hold the arch have stretched out, the spring ligament or deltoid ligament may be repaired or reconstructed. In some cases, a bone wedge is inserted into the midfoot to recreate the arch.
For rigid flat feet or cases where joint damage is severe, fusion of one or more midfoot joints may be necessary. This eliminates motion at those joints but provides a stable, pain-free foot. Recovery from flat foot surgery varies by procedure but generally involves several weeks of non-weight-bearing followed by a gradual return to walking, often in a boot. Full recovery can take six months to a year.
Flat Feet in Children
Parents often worry when their toddler’s feet look flat, but in the vast majority of cases this is completely normal. The arch is still developing and won’t reach its mature shape until around age six. Flexible flat feet in young children rarely need treatment. If a child has no pain and moves normally, observation is all that’s needed.
The picture changes if a child’s flat feet are rigid, painful, or still present after age 10. Some clinicians recommend intervening before age six when symptoms are present, while others prefer to wait since many cases resolve on their own. If your child complains of foot or leg pain during activity, tires easily during walking, or has noticeably stiff feet, an evaluation is worthwhile.