PTTD vs Flatfeet: What’s Actually the Difference?

If you’ve been researching foot pain, you’ve probably encountered two terms that seem to overlap: PTTD (posterior tibial tendon dysfunction) and flatfeet. Are they the same thing? Is one caused by the other? And does it even matter? Let’s clear up the confusion.

Key Definitions First

Flatfoot (also called pes planus) is a structural condition where the arch of the foot collapses, causing the entire sole to touch the ground when standing. It’s a description of foot shape, not a diagnosis of what’s causing it.

Posterior tibial tendon dysfunction (PTTD) is a specific problem with a particular tendon—the posterior tibial tendon that runs along the inside of your ankle and foot. When this tendon becomes damaged, inflamed, or weak, it can no longer support the arch, leading to a flattened appearance.

Here’s the key relationship: PTTD is one of the most common causes of acquired flatfoot in adults.

Types of Flatfoot

Not all flatfeet are created equal. Understanding the type helps explain the relationship with PTTD:

Congenital Flatfoot

This is a flatfoot present from birth. Some people never develop an arch—it’s just how their feet formed. Congenital flatfoot is often:

  • Flexible: The arch appears when not bearing weight or when on tiptoes
  • Asymptomatic: Many people with congenital flatfeet never have pain or problems
  • Usually bilateral: Affecting both feet equally

Acquired Flatfoot

This develops later in life, typically due to another problem. PTTD is the #1 cause of acquired flatfoot in adults, but other causes include:

  • Tarsal coalition: An abnormal connection between foot bones
  • Trauma or injury: Fractures or dislocations can change foot structure
  • Arthritis: Joint degeneration can cause the foot to collapse
  • Posterior tibial tendon dysfunction: The tendon simply can’t do its job

How PTTD Causes Flatfoot

The posterior tibial tendon has an important job: it supports the arch and helps with inversion (turning the foot inward). When this tendon fails:

  1. The arch gradually collapses
  2. The heel rolls inward (overpronation)
  3. The foot appears flatter
  4. Pain develops along the tendon path
  5. The deformity can become rigid if untreated

This is why many people first notice PTTD when their previously normal arch seems to be “disappearing.”

How to Tell the Difference

It can be hard to distinguish between PTTD and other types of flatfoot, but here are some clues:

Signs Pointing to PTTD

  • Pain along the inner ankle and foot: Especially during activity or after prolonged standing
  • Recent onset: Your arch used to be normal and recently changed
  • Swelling: Visible swelling along the tendon path
  • Single-sided: Often affects one foot first (though it can affect both)
  • Progressive: Symptoms worsen over time without treatment

Signs of Congenital/Non-PTTD Flatfoot

  • Lifelong history: You’ve had flat feet since childhood
  • No pain: Many people with congenital flatfeet are completely asymptomatic
  • Flexible: The arch returns when not weight-bearing
  • Bilateral: Both feet affected equally
  • Stable: The condition doesn’t change or worsen significantly

The Self-Test You Can Do

The “too many toes” sign is a simple at-home check:

  1. Stand facing away from a mirror (or have someone look from behind)
  2. Look at your feet from behind
  3. If you see more toes than normal on the inside of your foot, your heel may be rolling outward (suggesting PTTD)

This isn’t a diagnosis, but it’s a useful observation to share with your doctor.

Why It Matters for Treatment

Understanding whether you have PTTD versus other types of flatfoot matters because the treatments differ:

PTTD Treatment

  • Early stages: Rest, ice, physical therapy, orthotics, medication
  • Moderate stages: More aggressive immobilization, bracing
  • Late stages: Surgery often needed to repair tendon and correct deformity

Congenital Flatfoot Treatment

  • Often requires no treatment if asymptomatic
  • If painful, may respond to orthotics, physical therapy
  • Surgery, if needed, focuses on bone structure rather than tendon repair

Getting the right diagnosis is crucial. Treating PTTD like simple flatfoot (or vice versa) can lead to ineffective treatment and wasted time.

What About Flexible vs Rigid?

You’ll also hear these terms:

  • Flexible flatfoot: The arch flattens when standing but returns when not bearing weight. Often congenital and often asymptomatic.
  • Rigid flatfoot: The foot remains flat regardless of position. Usually indicates more advanced structural problems, including late-stage PTTD.

Rigid flatfoot almost always requires more aggressive treatment and has a poorer prognosis without intervention.

The Bottom Line

Here’s the simple version:

  • Flatfoot describes a foot shape—an arch that’s collapsed
  • PTTD is a specific tendon problem that CAUSES acquired flatfoot
  • Not all flatfeet is PTTD—some people are born with flat feet and never have problems
  • PTTD is the main cause of adult-onset flatfoot

If you have flat feet and pain, especially if it’s new, see a podiatrist or orthopedic specialist. They can determine whether PTTD or another cause is behind your symptoms—and guide you to the right treatment.

Sources

  • Mayo Clinic: “Flatfeet” overview
  • American College of Foot and Ankle Surgeons (ACFAS): PTTD clinical guidelines
  • Journal of Foot and Ankle Research: PTTD and acquired flatfoot relationship