Flatfoot (Pes Planus) in Adults: When to Seek Treatment

What Is Adult Flatfoot?

Flatfoot (pes planus) describes a foot where the medial arch is reduced or absent, causing the entire sole to contact the ground. While some people are born with flat feet (flexible flatfoot) and have no pain, adult-acquired flatfoot is a progressive condition that develops in adults — often due to dysfunction of the posterior tibial tendon.

The most common cause in adults is Posterior Tibial Tendon Dysfunction (PTTD) — also called adult-acquired flatfoot deformity (AAFD).

The Posterior Tibial Tendon

The posterior tibial muscle and its tendon run along the inside of the ankle and foot, attaching to the navicular bone and multiple midfoot bones. Its primary functions:

Supports the medial arch during the stance phase of walking
Supinates the subtalar joint during push-off, allowing the foot to become a rigid lever

When this tendon degenerates, tears, or becomes incompetent, the arch progressively collapses.

Stages of Adult Acquired Flatfoot

Stage	Description	Treatment
Stage I	Tendon inflammation/pain; normal arch; no deformity	Conservative
Stage II	Flexible flatfoot deformity; tendon elongated/torn; arch collapses but can be passively corrected	Conservative or surgical soft tissue reconstruction
Stage III	Rigid flatfoot; fixed deformity; subtalar joint arthritic	Surgical joint fusion
Stage IV	Ankle joint involvement; valgus ankle	Complex surgical reconstruction

Causes and Risk Factors

Age: Most common 40–60 years
Female sex: More common in women
Obesity: Increases tendon load
Hypertension and diabetes: Associated with posterior tibial tendon degeneration
Prior inflammatory arthritis
Injury to the posterior tibial tendon

Symptoms

Inner ankle pain and swelling: Along the course of the posterior tibial tendon, below and behind the medial malleolus
Arch pain and fatigue
Difficulty with activities: Standing for prolonged periods, walking, stair climbing
Progressive deformity: "Too many toes" sign — standing behind the patient, more toes visible on the affected side due to forefoot abduction
Loss of single-heel rise: Inability to rise on tiptoe on the affected foot (tests posterior tibial tendon function)

Diagnosis

Clinical examination: "Too many toes" sign, single-heel rise testing, palpation of the tendon
Weight-bearing foot and ankle X-rays: Assess arch collapse, forefoot abduction, hindfoot valgus
MRI: Evaluates tendon integrity, degree of tearing, and surrounding structures

Treatment

Conservative Treatment

Stage I and early Stage II:

Orthotics (arch supports): Custom-molded orthotics with medial arch support and heel posting
UCBL (University of California Biomechanics Laboratory) orthosis: Rigid orthosis that controls hindfoot valgus
Arizona ankle-foot orthosis (AFO): For more advanced deformity requiring more rigid control
Walking boot: For acute flares of tendon pain
Physical therapy: Posterior tibial tendon strengthening, single-leg heel rise exercises, calf stretching
NSAIDs: Acute pain management

Surgical Treatment

For Stage II failing conservative treatment, and Stages III–IV:

Stage II flexible deformity: Posterior tibial tendon debridement ± reconstruction, combined with bony procedures (calcaneal osteotomy to correct heel alignment, medial column fusion for forefoot abduction)
Stage III–IV rigid deformity: Hindfoot and/or midfoot fusion

Recovery from reconstructive surgery: 6–12 months to full recovery.