Flat Feet

Flat feet, also known as pes planus, is a common condition in which the arch on the inside of the foot flattens under load, so that most or all of the sole makes contact with the ground when standing. For many people, this is simply a lifelong variation in foot shape that never causes a problem. For others — particularly when an arch that was previously normal begins to collapse in adulthood — flat feet can be the sign of a genuine, progressive problem with the tendons and ligaments that support the foot.

This distinction matters more than most people realise. Flat feet in children is usually a normal part of development that resolves on its own and needs no treatment. Flat feet that develops or worsens in adulthood is a different condition altogether, most often caused by gradual failure of a specific tendon, and it can progress from mild discomfort to a rigid, disabling deformity if left unaddressed. Understanding which category applies to you — and why — is the key to knowing whether flat feet is something to simply live with or something that needs active management.

How the Arch of the Foot Works

The arch of the foot is not a single structure but a coordinated system of bones, ligaments, and tendons that work together to support body weight, absorb shock, and adapt the foot to uneven ground. Several structures are especially important:

• The posterior tibial tendon: It runs from a muscle in the calf, behind the inner ankle bone, to attach along the underside of the midfoot. It provides more than half of the dynamic support for the arch during walking, and is the single most important structure in maintaining arch height in adults.
• The spring ligament: A strong ligament on the underside of the foot that supports the head of the talus bone, working alongside the posterior tibial tendon to maintain the arch.
• The plantar fascia: A thick band of tissue along the sole of the foot that provides additional passive support to the arch, particularly during the push-off phase of walking.

When these structures function normally, the arch flattens slightly and then springs back with each step, acting as an efficient shock absorber. Flat feet develops when this system does not provide adequate support, either because it never fully formed that way (as in many children and some adults with lifelong flexible flat feet), or because one or more of these supporting structures has weakened, stretched, or torn over time.

Flexible vs. Rigid Flat Feet: The Key Distinction

Almost every discussion of flat feet, and every treatment decision, hinges on one question: does the arch reappear when the foot is not bearing weight, or when standing on tiptoe? This single distinction separates two very different situations.

• Flexible Flat Feet: The arch is visible when sitting or standing on tiptoe, but flattens under weight-bearing load. This is by far the more common pattern, seen in the great majority of children with flat feet and in many adults with lifelong flat feet who have never had any problems. Flexible flat feet is usually painless and does not require treatment unless it is causing symptoms.
• Rigid Flat Feet: The arch remains flat regardless of weight-bearing or foot position — it does not reappear on tiptoe. This pattern suggests a structural or degenerative problem, such as a tarsal coalition (an abnormal fusion between bones in the foot present from childhood) or advanced adult-acquired flatfoot deformity, and generally warrants further assessment.

Causes of Flat Feet

The cause of flat feet differs significantly depending on whether it has been present since childhood or has developed later in life, and this distinction directly shapes how concerned to be and what treatment, if any, is appropriate.

• Paediatric Flexible Flat Feet: The most common cause overall. Present from early childhood as the arch is still developing, typically painless, and in the large majority of children resolves naturally without any treatment as the foot's ligaments mature through adolescence.
• Adult-Acquired Flatfoot: The most common cause of flat feet developing in adulthood. Chronic strain or degeneration causes the posterior tibial tendon to gradually weaken and, eventually, fail, allowing the arch to collapse progressively over months to years. Distinct from childhood flat feet — it is a degenerative process affecting a foot that was previously normal, not a continuation of childhood flat feet.
• Tarsal Coalition: An abnormal bony or fibrous connection between two or more bones in the foot, present from birth but often only becoming symptomatic in adolescence as the coalition stiffens. A common cause of rigid, rather than flexible, flat feet in younger patients.
• Diabetes-Related Nerve and Joint Damage: Nerve damage from diabetes can lead to progressive breakdown of the bones and joints of the foot, severely compromising the structures that support the arch and causing significant, sometimes rapid, deformity.
• Arthritis: Both degenerative and inflammatory forms of arthritis can damage the joints and supporting ligaments of the midfoot and hindfoot, leading to progressive flattening.
• Injury: Fractures or ligament injuries affecting the midfoot or hindfoot can disrupt the structures that maintain arch height, sometimes causing a sudden, rather than gradual, flattening.

Symptoms of Flat Feet

Flat feet does not always cause symptoms, and many people live with flexible flat feet their entire lives without any problems. When symptoms do occur, they can affect the foot directly or show up elsewhere in the leg or back due to changes in gait and alignment.

• Foot pain, particularly in the heel or arch area
• Swelling along the inside of the ankle
• Pain along the shin bone
• Pain in the hips or lower back
• Fatigue in the feet or legs after standing or walking
• Difficulty or inability to rise fully onto the toes on the affected side

If the underlying cause progresses without treatment, further symptoms can develop over time:

• Chronic pain, including pain at rest
• Secondary deformities such as bunions or hammertoes
• A visibly altered gait or difficulty with footwear fit
• Pain or arthritis developing in the outer ankle, as the collapsed arch changes how load passes through the foot

Risk Factors for Flat Feet

Factors that can increase your risk of flatfoot include:

• Obesity: It increases the mechanical load the arch must support
• Previous injury to the foot or ankle
• Arthritis
• Ageing: Tendons and ligaments naturally lose some strength and elasticity over time
• Diabetes, particularly with associated nerve damage
• Female sex and midlife: Posterior tibial tendon dysfunction is more commonly diagnosed in women over 40
• High blood pressure, which has been associated with a higher risk of posterior tibial tendon dysfunction in some studies

How is Flat Feet Diagnosed?

• Clinical Examination: Assessment of arch shape while standing, sitting, and on tiptoe (the “too many toes” sign — where more toes than expected are visible from behind due to forefoot misalignment — is a classic finding), along with strength testing of the posterior tibial tendon and assessment of joint flexibility.
• Weight-Bearing X-ray: Taken with the patient standing, to accurately assess the degree of arch collapse and bone alignment under normal load — imaging taken without weight-bearing can significantly underestimate the deformity.
• Ultrasound: Can assess the posterior tibial tendon for inflammation, thickening, or tearing, and is a useful, accessible first-line imaging option.
• MRI: Provides detailed imaging of the posterior tibial tendon, spring ligament, and surrounding soft tissue, useful for confirming the extent of tendon damage and planning surgery when needed.
• CT Scan: Particularly useful for assessing bony alignment in more advanced deformity, and for identifying a tarsal coalition as the underlying cause of a rigid flat foot.

Living with Flat Feet

• Choose supportive, well-fitted footwear with adequate arch support, particularly for prolonged standing or walking
• Maintain a healthy weight to reduce ongoing load on the arch
• If you have been prescribed orthotics or a brace, wear them consistently as advised, since inconsistent use reduces their effectiveness
• Keep up with any prescribed calf and tendon strengthening exercises, even once symptoms improve
• Monitor for any new or worsening inner ankle pain, visible change in arch height, or increasing difficulty rising onto your toes — these warrant reassessment rather than being managed indefinitely with the same approach
• If you have diabetes, inspect your feet regularly and seek prompt attention for any new deformity, swelling, or wound, given the added risk of rapid joint breakdown