What Is Congenital Pes Planus? Causes and Treatment

Congenital pes planus is a flatfoot deformity present from birth or early childhood, in which the medial longitudinal arch of the foot is reduced or absent when the child stands. Most cases are flexible, meaning the arch appears when the foot is unloaded and flattens under weight, and the vast majority of these children are pain-free and develop normally without intervention. A smaller but clinically important group has rigid flatfoot, where the arch stays flat regardless of position, often due to structural abnormalities like tarsal coalitions or congenital vertical talus. The line between a foot that simply hasn’t finished developing its arch yet and one that needs medical attention is not always obvious, which is why the condition generates so much parental anxiety and so many clinic visits.

How the Arch Develops and Why So Many Toddlers Look Flat-Footed

Babies and toddlers almost universally have flat-looking feet. A generous fat pad fills the arch area, and the bones, ligaments, and muscles that form the arch are still maturing. The medial longitudinal arch typically becomes visible between ages three and six, though development continues well into the school-age years. Because of this normal timeline, a flat-appearing foot in a two-year-old is not a diagnosis; it’s a developmental stage.

Flatfoot is the leading reason parents bring children in for foot-related orthopedic visits, and reported prevalence numbers vary widely depending on the age group studied and the measurement method used.¹ The key clinical question is whether the flatfoot is flexible or rigid, because the two categories have very different causes and very different treatment paths.

Flexible Versus Rigid Flatfoot

In a flexible flatfoot, the arch vanishes when the child stands but reappears when they sit, stand on tiptoe, or extend the big toe. The foot moves freely through its full range of motion. This is by far the more common type and is often called “physiologic” flatfoot because it represents a normal variant of foot shape rather than a structural problem. Most children with flexible flatfoot have no pain, no functional limitation, and no need for treatment.

Rigid flatfoot is a different story. The arch is absent in every position, and the foot’s motion is restricted. The two most frequent structural causes in children are tarsal coalitions and congenital vertical talus. Tarsal coalitions are abnormal bridges of bone, cartilage, or fibrous tissue that fuse two or more bones in the hindfoot or midfoot. These coalitions are recognized as the primary cause of painful rigid flatfoot in children and adolescents.² Among the coalition types, talocalcaneal coalitions frequently produce flatfoot deformity.³

Congenital vertical talus is rarer but more dramatic. The talus bone sits in a vertical orientation, and the navicular bone dislocates upward and outward, producing a rigid “rocker-bottom” sole with a prominent heel.⁴ More severe rocker-bottom deformities are associated with this diagnosis compared to the milder oblique talus variant.⁵ Congenital vertical talus is usually identified in infancy because the foot’s shape is visibly abnormal from the start.

There is also an intermediate category worth knowing about: flexible flatfoot with a short Achilles tendon. Unlike simple flexible flatfoot, this subtype is known to cause pain and disability in some adolescents and adults because the tight heel cord restricts the ankle’s upward motion and places abnormal stress on the midfoot.⁶ Identifying a tight Achilles tendon during examination can change the treatment approach significantly.

What Causes Congenital Pes Planus

The causes depend on which type of flatfoot you’re talking about. Simple flexible flatfoot is driven by a combination of ligament laxity, muscle tone, body weight, and the still-developing skeletal structure. It runs in families, and there’s often no single identifiable cause beyond the child’s inherited foot shape.

For congenital vertical talus, there’s clearer evidence of genetic involvement. About half of children with isolated congenital vertical talus have an affected first-degree relative, and the condition has been reported to follow an autosomal dominant inheritance pattern in many families, though incomplete penetrance makes the pattern hard to pin down definitively.⁷ One specific genetic finding has been identified: a mutation in the HOXD10 gene was found to segregate with congenital vertical talus in a large British family, though the same mutation was not found in other families with the condition, suggesting that more than one gene can be responsible.⁸ Congenital vertical talus also appears as a feature of several well-established genetic syndromes, which further supports the idea that genetic factors play a significant role.

Tarsal coalitions, meanwhile, arise from a failure of the normal segmentation process during fetal development. Instead of the tarsal bones separating fully, abnormal connections persist between them. The exact trigger is not well understood, but the condition appears to have a hereditary component as well.

Connective Tissue Conditions and Joint Hypermobility

Conditions that affect connective tissue can produce an especially severe form of flatfoot. Children with hypermobile Ehlers-Danlos syndrome, for example, have abnormal mobility in all lower-extremity joints, which can lead to a progressive and extreme form of pes planus.⁹ In these children, the flatfoot tends to worsen over time rather than improving on its own, and surgical intervention may eventually be needed.

A common assumption among clinicians and parents is that general joint hypermobility (the “double-jointed” flexibility many children have) directly causes flatfoot. The evidence on this is not as clear-cut as you might expect. At least one study of preschool-age children found no correlation between joint hypermobility, as measured by the standard Beighton score, and flexible flatfoot.¹⁰ The distinction matters: having a named connective tissue disorder like Ehlers-Danlos is different from simply being a flexible child. The former reliably produces foot problems; the latter may not.

How It Affects Movement

One question parents often have is whether flat feet actually hold their child back physically. The biomechanical research suggests they can, at least measurably. Children with flexible flatfoot show altered gait patterns, including a lower medial arch throughout the walking cycle, increased hindfoot valgus (the heel tilting outward), and increased forefoot abduction (the front of the foot angling outward).¹¹ These changes affect how forces travel through the foot and leg during walking.

When it comes to running, the differences are more pronounced. Children with flexible flat feet show reduced running speed, shorter stride length, and decreased ankle power during push-off.¹² Tests of explosive power and dynamic balance tell a similar story: flat-footed boys performed worse on standing broad jumps, hop-for-distance tests, balance tests, and sprint speed, with small-to-moderate differences across the board.¹³

It’s worth keeping these effect sizes in perspective. The differences are real and statistically meaningful, but they are generally small to moderate. Plenty of flat-footed children are active and athletic. The findings are more useful for understanding the biomechanics of the condition than for predicting whether any individual child will struggle in sports.

Encouragingly, gait patterns in children with flatfoot tend to improve as their arch develops, though the improvement in how they walk lags somewhat behind the structural change in the foot itself.¹⁴

Quality of Life

Children with symptomatic flexible flatfoot report lower quality-of-life scores compared to typically developing peers, particularly in the physical domain. A study comparing children aged eight to fifteen found that those with flatfoot had meaningfully decreased scores on health-related quality-of-life questionnaires.¹⁵ The specific gait characteristics that most strongly predicted lower quality-of-life scores were increased hindfoot eversion and increased forefoot supination, and these correlated with slower walking speed and shorter stride length.¹⁶

The emphasis here is on symptomatic flatfoot. Most children with flexible flat feet are asymptomatic and their quality of life is not affected. The children who do report problems typically have foot pain, fatigue with prolonged activity, or difficulty keeping up with peers, and these are the ones for whom treatment discussions become relevant.

Diagnosis

Assessment typically begins with visual inspection and a few simple clinical tests. The “Jack test,” in which the examiner lifts the big toe, reveals whether the arch reconstitutes, confirming flexibility. A tiptoe test serves a similar purpose. The examiner also checks Achilles tendon tightness, hindfoot alignment, and overall joint mobility. These bedside maneuvers are usually enough to distinguish flexible from rigid flatfoot and to identify a tight heel cord.

When rigid flatfoot is suspected, or when a flexible flatfoot is painful and not responding to initial management, imaging comes into play. Standard weight-bearing X-rays of the foot allow measurement of key angles. For tarsal coalitions, a CT scan is often needed to fully characterize the abnormal connection. MRI may be helpful for detecting fibrous coalitions that don’t show up on X-ray or CT.

Conservative Treatment

The first-line approach for symptomatic flexible flatfoot is conservative, and it centers on three pillars: orthotic insoles, targeted exercises, and activity or footwear modification.

Custom-made arch support insoles have the strongest evidence base among conservative interventions. A randomized trial found that custom insoles produced greater pain reduction and larger functional improvements compared to standard footwear in children with symptomatic flexible flatfoot, and parental satisfaction was higher in the insoles group.¹⁷ Another trial at twelve weeks showed improvements in mobility and physical health scores with custom arch supports.¹⁸ Longer-term use of foot orthoses has been shown to favorably affect walking mechanics, including ankle and knee alignment and ground reaction forces.¹⁹

An important distinction exists between treating symptoms and changing the foot’s development. One study comparing children in corrective orthotic shoes to those in regular shoes found that the corrective shoes did not change the natural course of arch development in children with moderate flexible flatfoot.²⁰ In other words, insoles may relieve symptoms and improve function while a child wears them, but they do not appear to permanently alter the arch. This is a frequent source of misunderstanding for parents who expect corrective footwear to “fix” their child’s foot shape.

Exercise programs aimed at strengthening the foot’s intrinsic muscles have shown promising results. A six-week rehabilitation program targeting the small muscles within the foot improved foot position and balance control in children with flat feet and excess body weight.²¹ A comparative study found that starting corrective exercises with intrinsic foot muscles before progressing to extrinsic muscle exercises was more effective at reducing navicular drop, a key measure of arch collapse.²² These exercises include things like toe curls, towel scrunches, and short-foot exercises that activate the muscles running along the sole.

When Surgery Becomes an Option

Surgery is reserved for the minority of cases where conservative treatment fails to relieve symptoms. For flexible flatfoot, the most commonly studied procedure is subtalar arthroereisis, in which a small implant is placed in the sinus tarsi (the natural channel between the talus and heel bones) to limit excessive inward rolling of the foot. Studies consistently show clinical and radiographic improvement after this procedure. In one series, pain scores dropped substantially, foot alignment angles improved, and all patients returned to sports within a year.²³

A systematic review of long-term outcomes found that subtalar arthroereisis in symptomatic pediatric flexible flatfoot produces satisfactory clinical and radiographic results with a manageable complication profile.²⁴ The choice of implant material matters somewhat. A systematic review comparing metallic to bioabsorbable implants found that both produced high satisfaction and good correction. However, metallic implants carried higher odds of persistent pain in the sinus tarsi area and a trend toward more frequent non-routine removal.²⁵ Bioabsorbable implants dissolve on their own over time, which avoids a second procedure for removal.

The biomechanical effects of arthroereisis are measurable. After surgery, plantar pressure shifts away from the medial (inner) side of the foot toward the lateral (outer) side, the center-of-pressure path shifts outward, and there are favorable changes in muscle activation patterns during walking.²⁶

For rigid flatfoot caused by tarsal coalitions, surgical treatment typically involves resecting (removing) the abnormal bone bridge, sometimes combined with flatfoot reconstructive procedures.²⁷ The goal is to restore normal motion between the affected bones and correct alignment. For congenital vertical talus, treatment has historically involved serial casting followed by surgery to reduce the dislocated navicular and realign the talus, a protocol that mirrors the approach used for clubfoot.

Flexible flatfoot with a tight Achilles tendon may require joint-preserving surgery that corrects the deformity if conservative measures like stretching and orthotics fail to relieve pain.⁶ In some of these cases, a rigid supination deformity of the forefoot is present and needs to be addressed simultaneously.

The Barefoot Question

A topic that frequently comes up in conversations about children’s foot development is whether shoes themselves contribute to flat feet. There is some evidence to consider. A large multicenter study comparing habitually barefoot children to shoe-wearing peers found that regular footwear use was associated with a reduction in foot arch height across all age groups, even after controlling for confounding factors.²⁸ A study of toddlers found that barefoot children developed a higher plantar arch and different gait characteristics compared to those who wore conventional shoes.²⁹

Minimalist shoes, which aim to replicate barefoot conditions while offering some protection, have been tested in children as well. A randomized trial found moderate improvements in balance with minimalist shoes, along with trends toward increased foot muscle size, though the muscle changes did not reach statistical significance.³⁰ These findings don’t mean shoes cause flatfoot, but they suggest that the foot’s intrinsic muscles and supporting structures may develop differently depending on the demands placed on them. More time barefoot or in minimalist footwear may encourage the muscles that support the arch to work harder, which could be relevant for children whose feet are still developing.

When to Act and When to Wait

For parents navigating a flatfoot diagnosis, timing is everything. The vast majority of flexible flatfoot cases resolve on their own as the child grows. Intervention is warranted when the child has pain, fatigues easily with activity, or has a rigid deformity. A tight Achilles tendon alongside a flat foot deserves attention even if the child isn’t currently symptomatic, because it predicts future problems. Congenital vertical talus needs early treatment, ideally beginning in infancy. Tarsal coalitions often become symptomatic around ages eight to twelve, when the coalition ossifies and further restricts motion.

One school of thought holds that even asymptomatic flatfoot in children should not be entirely ignored, because every step on a deformed foot may lead to excessive tissue strain and secondary effects on knee, hip, and spinal alignment over time.³¹ This view is not universally shared. Many orthopedic specialists still consider asymptomatic flexible flatfoot a normal variant that needs monitoring but not active treatment. The lack of long-term studies tracking flat-footed children into middle age makes it difficult to settle this debate conclusively. What is well established is that when symptoms are present, early conservative treatment with orthotics and targeted exercises can improve function and comfort, and when those fail, surgical options have a solid track record of producing good outcomes.