A 45-year-old woman with a 10-year history of pes planus presents with progressive medial ankle pain, inability to perform single-heel-rise on the affected side, and collapse of the medial longitudinal arch. On observation, the 'too many toes' sign is present. The most likely diagnosis and the structure primarily responsible is:

• A Plantar fasciitis; plantar aponeurosis degeneration
• B Posterior tibial tendon dysfunction (PTTD); tibialis posterior tendon insufficiency ✓
• C Spring ligament rupture; calcaneonavicular ligament disruption
• D Tarsal coalition; talocalcaneal bar

Explanation

Posterior tibial tendon dysfunction (PTTD) is the most common cause of adult-acquired flatfoot deformity. The tibialis posterior is the primary dynamic invertor and the main supporter of the medial longitudinal arch; its insufficiency allows the peritalar joints to collapse into valgus. Clinical hallmarks include: inability to perform single-leg heel rise (the hallmark test), medial ankle pain, progressive planovalgus, and the 'too many toes' sign (excessive lateral toe visibility when viewed from behind due to hindfoot valgus and forefoot abduction).

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.