PTTD vs Flatfoot: What’s the Difference?

This is one of the most common questions about PTTD, and the answer matters because one is a medical condition that needs treatment, while the other is often just a foot type.

The key relationship: PTTD is one of the main causes of acquired flatfoot — meaning flat feet that develop in adulthood due to tendon dysfunction. When the posterior tibial tendon weakens or fails, it can no longer support the arch, and the foot gradually flattens. This is sometimes called “adult acquired flatfoot deformity.”

But not all flat feet are PTTD. Many people have flexible flatfeet their entire lives — they’ve been flat since childhood, the arch returns (or partially returns) when they sit down or lift their heels, and they have no pain. This is called congenital or flexible flatfoot, and it’s usually not a problem.

The difference in a nutshell:

• Congenital/flexible flatfoot: You’ve had it since childhood, it’s usually painless, and your arch returns when not standing.
• PTTD (acquired flatfoot): Develops in adulthood, gets progressively worse, causes pain, and your arch stays flat even when you’re off your feet.

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The bottom line: if you’ve noticed your feet getting flatter as an adult, especially if it’s accompanied by pain along the inner ankle, that’s not normal aging — it’s worth getting evaluated. PTTD is a progressive condition that typically gets worse without treatment.