Flat Foot (Pes Planus)

Definition

Classification

• Bailey and Love's, 28th Ed.

Causes

Physiological / Developmental

• Normal variant (most common) - frequently familial, almost always bilateral
• Ligamentous laxity / hyperlaxity syndromes (e.g. Marfan syndrome)

Acquired (Pathological)

• Tibialis posterior tendon dysfunction (PTTD) - most common cause of Adult Acquired Flatfoot Deformity (AAFD)
• Spring (calcaneonavicular) ligament rupture
• Tarsometatarsal arthritis/injury
• Charcot neuroarthropathy (e.g. diabetes)
• Inflammatory/degenerative arthritis (subtalar, talonavicular, naviculocuneiform joints)

Rigid Flatfoot

• Tarsal coalition (failure of mesenchymal segmentation) - affects 1 in 100 people, 50% bilateral, typically presents in adolescence
• Bailey and Love's 28th Ed.; Miller's Review of Orthopaedics, 9th Ed.

Clinical Features

• Medial ankle/foot pain early in AAFD
• Progressive arch collapse
• Lateral ankle pain late (due to subfibular impingement)
• Aching midfoot, pretibial pain

• Asymmetric hindfoot valgus (standing)
• Depressed arch
• Abducted forefoot
• "Too-many-toes" sign: viewed from behind, more than 5 toes are visible lateral to the heel on the affected side - indicates forefoot abduction in AAFD

• Single-limb heel rise test: inability or pain = significant PTT dysfunction
• Windlass test: ask patient to stand on tiptoes - arch should form; failure = fixed flat foot
• Jack's test: with patient standing, lift great toe - arch should reconstitute in flexible flat foot; failure = fixed flat foot

Radiographic Assessment

• C-sign / dorsal talar beaking on X-ray (middle facet / talocalcaneal coalition)
• Elongated anterior process of calcaneus on lateral view (calcaneonavicular coalition)
• CT scan for definitive evaluation

AAFD / PTTD Staging & Treatment

Stage I - Tenosynovitis, no deformity

• Conservative: Immobilization (cast or boot), then arch support/medial heel wedge orthotic
• Surgical: PTT synovectomy

Stage II - Flexible deformity; PTT functionally incompetent

• Conservative (first-line, at least 6 months): Ankle-foot orthosis (AFO) + physiotherapy (highest success rate); full-length orthotic with arch support + medial heel wedge
• Surgical (if conservative fails):
  • FDL or FHL tendon transfer into navicular to reconstruct PTT
  • Gastrocnemius recession (if contracture present)
  • Spring ligament reconstruction (synthetic tape augmentation now widely accepted)
  • Stage IIA (hindfoot valgus, <40% TN uncoverage): Medial slide calcaneal osteotomy
  • Stage IIB (hindfoot valgus + significant forefoot abduction): Lateral column lengthening (Evans osteotomy) ± medial slide osteotomy

Stage III - Fixed (rigid) deformity

• Surgical: Triple arthrodesis (subtalar + talonavicular + calcaneocuboid)

Stage IV - Stage III + ankle valgus/arthritis

• TAR (total ankle replacement) or tibiotalar + subtalar arthrodesis

Flexible Pes Planus (Pediatric / Physiological)

• Foot is flat only with standing; arch reconstitutes with toe-walking or non-weight-bearing
• Commonly associated with ligamentous laxity and mild lower extremity rotational problems
• Asymptomatic cases: observation only; orthoses do NOT alter natural history
• Symptomatic cases: arch supports and shoes with stiffer soles for pain relief (not corrective); surgical correction reserved for severe cases failing extensive non-operative treatment
• Miller's Review of Orthopaedics, 9th Ed.

Tarsal Coalition

• Rigid flat foot in an adolescent should raise suspicion
• Peroneal muscle spasm is a consequence, not a cause, of tarsal coalition (peroneal spastic flat foot)
• Types: calcaneonavicular (most common, may have some residual motion), talocalcaneal (middle facet most common)
• Treatment: resection (if <50% of middle facet involved); arthrodesis if >50% or severe deformity
• Campbell's Operative Orthopaedics, 15th Ed. 2026; Miller's Review of Orthopaedics, 9th Ed.

Summary of Key Points

• The painless, flexible flat foot needs no treatment in most cases
• The symptomatic rigid flat foot requires investigation (tarsal coalition, PTTD)
• PTTD is the most common cause of AAFD in adults; occurs especially in overweight women
• The single-limb heel rise test is the most important clinical test for PTT integrity
• Orthoses do not correct deformity but can provide symptomatic relief
• Surgery is a major undertaking but is highly successful at achieving symptomatic relief in carefully selected patients