Flat Foot: Causes, Symptoms, and Treatment

Flat foot

Flat foot (or pes planus) is a condition in which the medial longitudinal arch of the foot is reduced or absent, resulting in a flattening of the plantar arch and complete contact of the sole of the foot with the ground. It is one of the most common structural alterations of the foot, present in 20-30% of the adult population.

It is important to distinguish between physiological flat foot (present in all children under 6 years of age, which in most cases resolves spontaneously with growth) and pathological flat foot (which causes symptoms and requires treatment). Many adults with flat feet are completely asymptomatic and do not require any treatment.

Flat foot becomes a clinical problem when it causes pain, fatigue, instability, or predisposes to other conditions such as plantar fasciitis, posterior tibial tendinitis, and metatarsalgia.

Anatomy: The Plantar Arch

The foot has three arches:

• Medial longitudinal arch: the most important and most visible — the inner arch of the foot that normally does not touch the floor. It is maintained by the plantar fascia, the posterior tibial tendon, the plantar ligaments, and the intrinsic muscles of the foot.
• Lateral longitudinal arch: the outer arch, lower and less evident.
• Transverse arch: the arch that crosses the forefoot.

The medial longitudinal arch has fundamental functions:

• Shock absorption: absorbs impact forces during walking and running.
• Propulsion lever: the “windlass” mechanism of the plantar fascia stiffens the arch during the push-off phase, transforming the foot into a rigid lever.
• Load distribution: distributes body weight between the heel and forefoot.

In flat foot, the arch collapses under load, compromising all these functions.

Types of Flat Foot

Flexible Flat Foot (the most common)

The arch is present without load (when the foot is lifted or on tiptoes) but collapses under body weight. It is the most common form (>90% of cases) and generally benign.

Test: when the patient stands on tiptoes, the arch reforms → flexible flat foot.

Rigid Flat Foot

The arch is absent both with and without load. It is less common and often associated with specific conditions:

• Tarsal coalition: a congenital bony fusion between two or more bones of the foot.
• Arthritis: rheumatoid arthritis, foot osteoarthritis.
• Post-traumatic sequelae: fractures of the foot or ankle.

Adult Acquired Flat Foot

Flat foot that develops in adulthood, in a previously normal foot, is typically caused by posterior tibial tendon dysfunction — the main muscle supporting the arch. Degeneration or rupture of this tendon causes progressive arch collapse.

Causes

In Children

• Physiological: all children are born with flat feet due to the presence of a fat pad under the arch and ligamentous laxity. The arch develops gradually and stabilizes between 6 and 10 years of age.
• Ligamentous hyperlaxity: children with very elastic ligaments tend to have flat feet for longer.
• Childhood overweight: excess weight slows down arch development.
• Tarsal coalition: rare cause of rigid flat foot.

In Adults

• Posterior tibial dysfunction: the most common cause of adult acquired flat foot. The tendon weakens and lengthens due to degeneration, overuse, or inflammation.
• Overweight and obesity: excess weight flattens the arch.
• Pregnancy: pregnancy hormones (relaxin) soften ligaments, weight increases — the foot flattens.
• Arthritis: inflammation and destruction of foot joints.
• Post-traumatic: fractures of the navicular, calcaneus, or ankle.
• Neuropathy: diabetes and other neuropathies weaken the intrinsic muscles of the foot.
• Aging: degeneration of tendons and ligaments with age.

Symptoms

Asymptomatic Flat Foot

Many adults with flat feet have no symptoms and do not require treatment. Flat foot is often a normal anatomical variant.

Symptomatic Flat Foot

• Foot pain: in the inner part of the foot (arch), in the inner part of the ankle (posterior tibial), under the heel.
• Foot fatigue: early fatigue during prolonged standing and walking.
• Calf pain: excessive pronation overloads the leg muscles.
• Knee pain: flat foot alters the biomechanics of the lower limb, favoring knee valgus and predisposing to patellar chondropathy and iliotibial band syndrome.
• Back pain: the alteration of the kinetic chain from the foot to the spine can contribute to low back pain.
• Calluses: formation of calluses on the inner part of the forefoot.
• Shoe deformation: the sole wears predominantly on the inner side.

Signs of Progression

In adult acquired flat foot (posterior tibial dysfunction):

• Stage I: pain and swelling along the course of the posterior tibial tendon, arch still present.
• Stage II: the foot progressively flattens, the heel deviates into valgus, tibial strength is reduced.
• Stage III: rigid flat foot with osteoarthritis of the foot joints.
• Stage IV: ankle involvement with valgus deformity.

Diagnosis

Clinical Examination

• Weight-bearing observation: assessment of the arch, heel position (valgus), foot shape.
• Tiptoe test: if the arch reforms on tiptoes → flexible flat foot.
• “Too many toes sign” test: looking at the foot from behind, if too many toes are visible laterally → the foot is abducted (sign of flat foot).
• Posterior tibial test: foot inversion strength, pain on palpation of the tendon.
• Jack test: passive dorsiflexion of the first toe reforms the arch (windlass mechanism).
• Mobility assessment: mobility of the hindfoot and forefoot.
• Footwear assessment: medial sole wear.

Imaging Diagnostics

• Weight-bearing foot X-ray: highlights arch flattening (reduction of Costa-Bertani angle), talonavicular coverage, and foot alignment.
• Ultrasound: assesses the condition of the posterior tibial tendon.
• MRI: in cases of suspected posterior tibial dysfunction or tarsal coalition.
• Baropodometry: analysis of plantar load distribution — useful for orthotic prescription.

Treatment

In Children

• Observation: up to 6 years of age, asymptomatic flexible flat foot does not require treatment — it is normal.
• Exercises: walking barefoot on natural terrains (sand, grass), walking on tiptoes and heels — promote arch development.
• Footwear: flexible shoes that allow natural foot development. Rigid “corrective” shoes are contraindicated because they hinder the work of the foot muscles.
• Orthotics: indicated only if the flat foot is symptomatic (pain, easy fatigue) or if it persists after 8-10 years of age.
• Surgery: rarely indicated, only for symptomatic rigid flat foot (e.g., tarsal coalition).

In Adults

Orthotic Inserts

Custom orthotic inserts are the first-choice treatment for symptomatic adult flat foot:

• Medial arch support: supports the longitudinal arch during weight-bearing.
• Medial hindfoot wedge: corrects heel valgus.
• Semi-rigid material: must support the arch without being too rigid.

Footwear

• Shoes with medial support and a rigid heel counter.
• Motion control shoes for runners.
• Avoid flat shoes without support (flip-flops, ballet flats, loafers).

Physiotherapy

• Posterior tibial strengthening: the most important exercise for adult flat foot.
• Intrinsic foot muscle strengthening: for active arch support.
• Calf stretching: tightness of the gastrocnemius and soleus contributes to arch collapse.
• Proprioceptive re-education: exercises on unstable surfaces to improve foot control.

Surgery

Indicated in advanced stages (III-IV) of posterior tibial dysfunction or in symptomatic rigid flat foot. Options include:

• Calcaneal osteotomy: hindfoot realignment.
• Posterior tibial reconstruction: tendon transfer.
• Arthrodesis: fusion of hindfoot joints (in advanced stages with osteoarthritis).

Exercises for Flat Foot

The plantar arch is a curved structure on the foot’s underside that absorbs shock, distributes body weight, and enables propulsion during walking and running. Exercises are fundamental for strengthening the muscles that support the arch and improving proprioception. Your doctor or physical therapist will adapt the program.

Intrinsic Muscle Strengthening

Short foot exercise (active arch) — the key exercise

[IMAGE: Person sitting with foot flat on the ground. The plantar arch actively lifts by shortening the foot, without flexing the toes. The toes remain extended and in contact with the floor, the heel remains still. The foot “shortens” and the arch rises. Lateral view with detail of arch lift and toes remaining on the ground.]

Towel curl

[IMAGE: Person sitting on a chair with a towel spread on the floor under the foot. The toes flex to curl the towel towards themselves. The heel remains on the ground. Lateral view with detail of toes gripping the towel.]

Marble pickup with toes

[IMAGE: Person sitting with marbles (or small objects) scattered on the floor in front of the foot. The toes pick up one marble at a time and place it in a container. Top view with detail of toes gripping the marble.]

Posterior Tibial Strengthening

Resisted inversion with elastic band

[IMAGE: Person sitting with legs extended. A therapeutic elastic band is fixed to a stationary point laterally and wrapped around the forefoot. The foot rotates inward (inversion) against the resistance of the elastic band. Front view with detail of the elastic band and the direction of movement.]

Single-leg calf raise

[IMAGE: Person standing on one leg (the affected leg). The heel lifts, shifting weight onto the balls of the feet, then slowly lowers. One hand rests on a support for balance. Lateral view with detail of heel lift and arch activation.]

Stretching

Gastrocnemius stretch

[IMAGE: Person standing facing a wall with hands resting on it. One leg is back with a straight knee and heel on the ground. The stretch is felt in the calf. Lateral view.]

Soleus stretch

[IMAGE: Person standing facing a wall with hands resting on it. One leg is back with a BENT knee and heel on the ground. The stretch is felt in the lower calf. Lateral view showing the difference from the gastrocnemius (bent knee).]

Proprioception

Single-leg barefoot stance

[IMAGE: Person standing barefoot on one leg, the other leg slightly raised. The arch of the foot activates to maintain balance. Arms are open for balance. Gaze is fixed on a point. Front view with detail of the supporting foot and arch activation.]

Walking on tiptoes and heels

[IMAGE: Two images side-by-side. Left: person walking on tiptoes with arms at their sides. Right: same person walking on heels with toes lifted. Lateral view of both positions.]

Timelines

Prevention

• Walking barefoot on natural surfaces (sand, grass): stimulates the intrinsic muscles of the foot.
• Foot exercises: short foot, towel curl, calf raises — daily.
• Footwear with medial support: avoid completely flat shoes for prolonged use.
• Weight management: overweight flattens the arch.
• Calf stretching: calf tightness contributes to arch collapse.

For more information, consult the Complete Guide to Foot and Ankle Pain.

Frequently Asked Questions (FAQ)

Frequently Asked Questions

Is flat foot in children a concern?

Physiological flat foot is common in children under six years old and often resolves spontaneously with growth. However, if a child experiences pain, instability, or other symptoms, a medical evaluation is warranted to determine if intervention is necessary.

Can flat foot be corrected in adults?

While the structural arch may not always be fully restored in adults, the symptoms associated with flat foot can be effectively managed. Conservative treatments, including specific exercises, orthotics, and guidance from a physical therapist, aim to alleviate pain and improve foot function.

Are orthotics necessary for life?

The long-term necessity of orthotics for flat foot varies depending on individual symptoms and the underlying cause. Many individuals find significant relief and improved function with orthotics, and their use may be adjusted over time based on symptom progression and the effectiveness of other treatments.

Does flat foot prevent sports?

Asymptomatic flat foot typically does not prevent participation in sports or physical activities. When flat foot causes pain, fatigue, or instability, these symptoms may limit athletic performance, but appropriate management through physical therapy and supportive devices can often facilitate continued engagement in sports.

Sources and Scientific References

1. Brijwasi T et al. (2023). A comprehensive exercise program improves foot alignment in people with flexible flat foot: a randomised trial. J Physiother. 69:42-46. DOI | PubMed
2. Hara S et al. (2023). The effects of short foot exercises to treat flat foot deformity: A systematic review. J Back Musculoskelet Rehabil. 36:21-33. DOI | PubMed
3. Turner C et al. (2020). A guide to the management of paediatric pes planus. Aust J Gen Pract. 49:245-249. DOI | PubMed
4. Kodithuwakku Arachchige SNK et al. (2019). Flatfeet: Biomechanical implications, assessment and management. Foot (Edinb). 38:81-85. DOI | PubMed
5. Gervis WH (1970). Flat foot. Br Med J. 1:479-81. DOI | PubMed