Adult-Onset Flat Feet: Causes & What to Do

What Are Adult-Onset Flat Feet?

Adult-onset flat feet refer to a low or collapsing foot arch that develops or becomes noticeably more pronounced during adulthood.

The medical literature commonly uses terms such as:

• Adult-acquired flatfoot

• Adult-acquired flatfoot deformity (AAFD)

• Acquired flatfoot

• Adult flatfoot

• Pes planovalgus

• Posterior tibial tendon dysfunction-related flatfoot

Adult-acquired flatfoot represents a spectrum rather than a single condition. It can range from relatively mild, flexible changes to more advanced deformity involving the foot and ankle.

This is different from someone who has had low arches since childhood.

For an overview of different arch types, see:

Normal Arch vs Low Arch vs High Arch: What's the Difference?

And if you want to understand whether an arch can naturally change over time:

Can Your Foot Arch Change Over Time?

Can You Develop Flat Feet as an Adult?

Yes. Adults can develop flat feet or experience progressive flattening of an existing arch.

The change may happen gradually and may initially be difficult to notice.

Some people first notice:

• One foot looking flatter than the other

• The inside of the ankle appearing different

• Shoes fitting differently

• Increased foot fatigue

• Pain along the inside of the foot or ankle

• A change in walking ability

• The arch appearing lower when standing

Adult-acquired flatfoot can involve progressive changes in the posterior tibial tendon and other structures supporting the medial arch.

However, simply noticing that your arch looks lower does not establish a diagnosis. Foot shape naturally varies between people, and a clinical assessment may be needed when the change is new, progressive or symptomatic.

What Causes Flat Feet in Adults?

Adult-onset flat feet can have several possible causes, including tendon dysfunction, ligament problems, injury, arthritis, repetitive loading and other conditions affecting the structures that support the arch.

Some common contributors include:

1. Posterior Tibial Tendon Dysfunction

The posterior tibial tendon runs along the inside of the ankle and attaches into the foot. It plays an important role in supporting the arch and controlling foot movement.

Dysfunction of this tendon is one of the most commonly described causes of adult-acquired flatfoot. It can involve tendinosis, elongation or tearing of the tendon and may be accompanied by failure of other supporting structures.

When the tendon becomes less effective, the medial arch can progressively flatten and the heel and forefoot may change position.

2. Repeated Loading and Tendon Degeneration

Tendons are exposed to repeated mechanical loading throughout everyday activities.

Over time, repetitive loading can contribute to degenerative changes in susceptible tissues.

Adult-acquired flatfoot associated with posterior tibial tendon dysfunction is often described as a progressive process involving tendon degeneration and failure of supporting structures rather than a single isolated event.

3. Foot or Ankle Injury

An injury can damage structures that contribute to arch support.

Examples may include:

• Ankle fractures

• Severe ankle sprains

• Tendon injuries

• Ligament injuries

• Direct trauma

Traumatic injury is among the recognized contributors to acquired flatfoot.

If your arch changed noticeably after an injury, it is worth discussing the change with a qualified healthcare professional.

4. Arthritis and Joint Changes

Arthritic or degenerative changes affecting joints of the foot and ankle can contribute to changes in foot structure and function.

Inflammatory arthropathy and osteoarthropathy have been described among potential causes associated with adult-acquired flatfoot.

5. Ligament Failure

The arch is not supported by one structure alone.

Several ligaments and other soft tissues contribute to maintaining foot alignment.

In adult-acquired flatfoot, posterior tibial tendon dysfunction can occur alongside failure of structures such as the spring ligament and other supporting tissues.

6. Age-Related Structural Changes

The tissues supporting the foot can change with age.

Age alone does not mean that everyone will develop flat feet, but degenerative changes in tendons, ligaments and joints can increase the possibility of structural changes in susceptible individuals.

Adult-acquired flatfoot is particularly described in middle-aged and older adults, although it can occur at different ages depending on the underlying cause.

7. Increased Mechanical Load

Higher mechanical demands on the foot can increase the forces experienced by its supporting structures.

Body weight, occupational activity, prolonged standing, walking and other repetitive loading factors may therefore be relevant when evaluating an acquired flatfoot.

Importantly, this does not mean that body weight alone causes adult-onset flat feet. The condition is multifactorial and can involve tendon, ligament, joint, anatomical and other factors.

What Does Posterior Tibial Tendon Dysfunction Have to Do With Flat Feet?

The posterior tibial tendon is one of the key dynamic supports of the medial arch.

It runs behind the inner ankle and into the foot.

During walking, it helps control the foot and contributes to maintaining the arch and producing an effective lever for movement.

When the tendon becomes dysfunctional, the foot may progressively lose some of its ability to maintain its normal alignment.

Research on adult-acquired flatfoot describes posterior tibial tendon insufficiency as a major contributor to the condition, often accompanied by failure of other ligaments and supporting structures.

This is why new flat feet in an adult should not automatically be treated as simply a cosmetic change.

What Are the Signs of Adult-Onset Flat Feet?

The signs can vary depending on the underlying cause and severity.

Possible signs include:

• A newly flattened or lower arch

• One foot becoming flatter than the other

• Pain along the inside of the foot

• Pain or swelling around the inside of the ankle

• Foot fatigue

• Difficulty standing for long periods

• Reduced walking endurance

• Changes in shoe fit

• A change in the appearance of the heel

• Difficulty performing certain movements

• Increasing difficulty walking

• Progressive change in foot shape

Medial ankle or hindfoot pain, swelling, altered foot shape and reduced walking ability are described among symptoms associated with posterior tibial tendon dysfunction.

What Does Adult-Acquired Flatfoot Look Like?

A progressive acquired flatfoot may involve more than just a lower arch.

Depending on the stage and underlying structures involved, clinicians may observe:

• Flattening of the medial longitudinal arch

• Heel valgus

• Forefoot abduction

• Changes in the relationship between the hindfoot and midfoot

These changes have been documented in the biomechanics and imaging literature on adult-acquired flatfoot.

One commonly discussed clinical observation is the "too many toes" sign, where more toes may be visible from behind because the forefoot shifts outward relative to the hindfoot. This finding is not sufficient by itself to diagnose a condition.

Can Adult-Onset Flat Feet Affect Only One Foot?

Yes.

Adult-acquired flatfoot can affect one foot more noticeably than the other.

A difference between the two feet can be particularly useful information when the change is new.

For example, you may notice:

• One arch is visibly lower

• One shoe wears differently

• One ankle appears more swollen

• One foot becomes painful

• One foot feels weaker

An asymmetrical or progressive change should not automatically be attributed to naturally low arches.

How Do You Know If Your Arches Are Falling?

A few simple observations can help you notice a change, although they cannot diagnose adult-acquired flatfoot.

Compare Both Feet

Stand barefoot and compare the two feet.

Look for:

• Differences in arch height

• Differences in heel position

• Differences in foot width

• Changes in overall foot shape

Compare Old and Recent Photos

If you have photographs of your feet from previous years, compare them with current photographs.

A noticeable change over time can be useful information to share with a clinician.

Check Your Shoes

Look at your regularly worn footwear.

Changes in:

• Wear pattern

• Fit

• Required shoe size

• Foot position inside the shoe

may provide clues that your foot mechanics have changed.

Pay Attention to Symptoms

Ask yourself:

• Is there new pain?

• Is there swelling?

• Is walking becoming harder?

• Is standing for long periods more uncomfortable?

• Is one foot changing more than the other?

If several of these occur together, professional assessment is more appropriate than relying only on an at-home arch test.

How Is Adult-Onset Flat Foot Diagnosed?

Diagnosis usually begins with a medical history and physical examination and may include imaging when appropriate.

A healthcare professional may evaluate:

• When the arch change began

• Whether the change is progressive

• Pain location

• Swelling

• Foot flexibility

• Ankle movement

• Tendon function

• Muscle strength

• Foot alignment

• Walking pattern

• Ability to perform specific movements

Depending on the situation, imaging such as X-rays, ultrasound or MRI may be considered to evaluate bones, joints, tendons and other structures.

Can You Diagnose Adult-Onset Flat Feet at Home?

You can identify signs that your arch may have changed, but you cannot reliably determine the underlying cause at home.

For example, a wet-foot test can help visualize the part of your foot that contacts the ground, but it cannot tell you whether a newly flattened arch is caused by tendon dysfunction, ligament problems, arthritis or another condition.

For understanding the wet-foot test itself:

Wet Foot Test: How to Check Your Arch Type at Home

And for measuring the arch:

How to Measure Your Foot Arch at Home

Is Adult-Onset Flat Foot the Same as Having Naturally Low Arches?

No.

This distinction is important.

Someone may naturally have a low arch without ever developing symptoms or experiencing progressive changes.

Adult-acquired flatfoot refers to a change or deformity that develops during adulthood and may involve failure of the structures supporting the arch.

In simple terms:

This is also why "flat feet" and "fallen arches" should not always be treated as interchangeable terms.

For that specific distinction, see:

Flat Feet vs Fallen Arches: What's the Difference?

Are Adult-Onset Flat Feet Serious?

They can range from a relatively mild, manageable problem to a progressive deformity that significantly affects foot function.

The seriousness depends on:

• Underlying cause

• Severity

• Whether the deformity is flexible or rigid

• Presence of pain

• Tendon function

• Joint involvement

• Progression over time

• Impact on walking and daily activities

Adult-acquired flatfoot is considered a spectrum of deformity rather than one uniform condition. More advanced cases can involve significant malalignment and disability.

Therefore, the most useful question is not simply:

"How flat is my foot?"

It is:

"Why has my foot changed, and is the change affecting its function?"

What Should You Do If Your Arches Are Falling?

If you have noticed a new or progressive change in your arch, the appropriate next step depends on your symptoms and the underlying cause.

1. Don't Ignore a Progressive Change

A gradual reduction in arch height accompanied by pain, swelling or functional changes deserves assessment.

Early evaluation can help identify whether the change is related to a tendon, ligament, joint or other problem.

2. Reduce Activities That Clearly Aggravate Symptoms

If prolonged standing, walking or high-impact activity makes your symptoms worse, temporarily modifying the activity may reduce irritation while you seek appropriate advice.

Activity modification is one of the conservative approaches described for symptomatic adult-acquired flatfoot.

3. Choose Comfortable, Supportive Footwear

Shoes can influence how the foot is loaded during everyday activity.

A comfortable shoe with an appropriate fit may be useful when symptoms are present.

However, footwear should not be considered a substitute for evaluation when the arch is progressively changing.

4. Consider Orthotic Support When Appropriate

Orthoses may be used as part of conservative management for some forms of adult-acquired flatfoot.

Their purpose can include supporting the arch and controlling aspects of foot alignment.

This does not mean that everyone with adult-onset flat feet needs an insole.

For the broader question:

Do Flat Feet Need Arch Support?

5. Follow an Appropriate Rehabilitation Program

Depending on the cause and severity, rehabilitation may involve strengthening, mobility work, balance exercises and progressive activity.

The exact program should be matched to the individual's condition rather than assuming that every person with flat feet needs the same exercises.

6. Get Assessed if Symptoms Persist or Progress

If the foot continues to change, becomes painful or starts interfering with walking, seek professional assessment.

Can Adult-Onset Flat Feet Be Treated Without Surgery?

Many cases can initially be managed with non-surgical approaches, particularly when the deformity is flexible and identified earlier.

Depending on the condition, conservative management may include:

• Activity modification

• Footwear changes

• Orthoses

• Bracing

• Physical therapy

• Strengthening

• Short-term immobilization in selected cases

• Symptom management

A review of adult-acquired flatfoot notes that nonoperative treatment is generally attempted first, particularly in earlier stages.

The American College of Foot and Ankle Surgeons also published a clinical consensus statement addressing the appropriate management of adult-acquired flatfoot deformity.

Treatment should therefore be based on the cause, stage, symptoms and functional impact, rather than the appearance of the arch alone.

Do You Need Insoles for Adult-Onset Flat Feet?

Not necessarily.

An insole may be considered when additional support is appropriate, particularly when the foot is flexible and symptoms are related to loading or alignment.

Research and clinical reviews describe orthotic devices as one component of conservative management for adult-acquired flatfoot.

But an insole cannot determine why your arch has changed.

If your arch has recently started flattening, it is more important to understand the underlying issue before assuming that an arch-support insole is the complete solution.

For more information:

Can Insoles Help Flat Feet?

How to Choose Insoles for Flat Feet

Can Exercise Help Adult-Onset Flat Feet?

Exercise may be incorporated into rehabilitation depending on the underlying condition.

Potential areas of focus can include:

• Calf strength

• Foot and ankle strength

• Posterior tibial muscle function

• Balance

• Lower-limb strength

• Mobility

• Movement control

However, exercises should not be presented as a universal way to "restore" every fallen arch.

When adult-acquired flatfoot is associated with tendon or ligament dysfunction, the appropriate exercise and rehabilitation strategy depends on the stage and severity of the condition.

Can Adult-Onset Flat Feet Be Reversed?

Whether an acquired flatfoot can be reversed depends on its cause, severity and stage.

Early, flexible deformities may respond to conservative treatment, while more advanced or rigid deformities can require more extensive management.

It is therefore misleading to promise that exercises, footwear or insoles can permanently "restore" every fallen arch.

A better goal may be to:

• Reduce symptoms

• Improve function

• Support the foot

• Limit aggravating loads

• Address the underlying cause

• Prevent or slow progression where possible

When Should You See a Doctor for Adult-Onset Flat Feet?

Consider getting evaluated if you notice:

• A newly flattened arch

• Progressive arch collapse

• One foot becoming flatter than the other

• Persistent inner ankle pain

• Swelling around the inner ankle

• Increasing difficulty walking

• Reduced ability to stand or walk for long periods

• New weakness

• A noticeable change in foot shape

• Increasing difficulty performing everyday activities

Particular attention is warranted when a structural change is progressive rather than stable.

Posterior tibial tendon dysfunction can present with medial ankle pain, swelling, changes in foot shape and reduced walking ability, and adult-acquired flatfoot can progress if the underlying structural problem continues.

Can Adult-Onset Flat Feet Affect Walking?

Yes. A progressive acquired flatfoot can affect foot alignment and the way forces are transmitted during walking.

Changes can involve:

• Arch height

• Heel alignment

• Forefoot position

• Foot stability

• Push-off mechanics

• Walking endurance

Research on adult-acquired flatfoot describes changes such as hindfoot eversion, lowering of the medial longitudinal arch and forefoot abduction.

For a deeper explanation of how flat feet interact with gait:

Flat Feet and Walking: How Foot Mechanics Affect Movement

Can Adult-Onset Flat Feet Cause Knee or Back Problems?

Changes in foot mechanics can be associated with changes elsewhere in the lower-limb movement chain, but a newly flattened arch should not automatically be assumed to be the cause of knee or back pain.

If you have both flat feet and knee pain, read:

Can Flat Feet Cause Knee Pain?

For back pain:

Can Flat Feet Cause Back Pain?

Keeping these topics separate helps distinguish adult-onset flatfoot as the structural issue from the potential symptoms or biomechanical consequences that may occur elsewhere.

Adult-Onset Flat Feet: Key Takeaways

Adult-onset flat feet are different from simply having naturally low arches.

The most important points are:

• Adults can develop flat feet later in life.

• Adult-acquired flatfoot can involve changes in tendons, ligaments and joints.

• Posterior tibial tendon dysfunction is a major contributor to adult-acquired flatfoot.

• Injury, degenerative changes and inflammatory or other medical conditions can also contribute.

• A newly flattened arch does not automatically mean that you have a serious condition.

• Pain, swelling, weakness, progressive deformity or reduced walking ability are more important warning signs.

• At-home tests can help you observe your feet but cannot establish the underlying cause.

• Conservative treatment may include activity modification, footwear changes, orthoses, bracing and rehabilitation depending on the condition.

• More advanced deformities may require specialist treatment.

• If your arch is progressively changing, especially if the change is accompanied by pain or reduced function, professional assessment is appropriate.

The key distinction is simple:

A naturally low arch may be a stable feature of your foot. A newly changing arch in adulthood can be a sign that something about the supporting structures of the foot has changed.