Posterior Tibial Tendon Dysfunction

Posterior tibial tendon dysfunction (PTTD) — also called adult-acquired flatfoot deformity (AAFD) — is the progressive failure of the posterior tibial tendon, which is the primary dynamic stabilizer of the medial arch. As the tendon weakens, stretches, and eventually ruptures, the medial arch collapses, the heel drifts into valgus, and the forefoot abducts — the classic "too many toes" sign on viewing the foot from behind.

It is most common in women over 40, people with obesity, hypertension, or diabetes, and those who stand on hard surfaces for long periods.

The single-leg heel rise test — inability to rise onto tiptoe on the affected side — is the key exam finding (the tibialis posterior inverts the heel during heel rise). Weight-bearing AP, lateral, and hindfoot alignment X-rays quantify arch collapse and heel valgus. MRI stages tendon degeneration. The Johnson-Strom / Myerson classification (stages I–IV) guides treatment.

Stages I–II with failed conservative management and stages III–IV typically require surgical correction.

External patient-education references and related OSI pages for additional background:

• Britannica — Ankle (anatomy)
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language