What is the etiology of pes planus in adults and children?

Etiology of Pes Planus

Pes planus has distinct etiologies in children versus adults: in children, it is primarily congenital and developmental, while in adults, it is most commonly acquired through posterior tibial tendon dysfunction.

Pediatric Pes Planus Etiology

Congenital and Developmental Causes

• Genetic determination occurs at fertilization, with genes controlling the size, shape, and angles of declination of the talus and calcaneus 1
• Chromosomal aberrations including duplication, deletion, breakage, inversion, translocation, and mosaicism can cause faulty foot development and pes planus 1
• Intrauterine factors such as extraembryonic membrane strands can entangle the developing foot plate, potentially establishing calcaneovalgus deformities 1
• Developmental interference with nerve trunk induction (related to lumbosacral plexus), embryonic rotations, osteogenesis, or myogenesis can result in pes planus 1

Normal Developmental Variant

• Flexible pes planus is part of normal development in up to 14% of children, with foot arches typically developing as musculature strengthens with age 2, 3
• The talar neck-calcaneal angle normally decreases from 30 degrees at birth to 24 degrees in adults, representing natural structural changes 1
• Up to 25% of the total population has a deficient medial longitudinal arch in at least one foot, indicating this can be a normal variant 3

Associated Syndromic Causes in Children

• 22q11.2 deletion syndrome presents with pes planovalgus associated with nonspecific lower leg/foot pains that may benefit from orthotics 4
• Cardio-facio-cutaneous syndrome demonstrates pes planus or planovalgus in two-thirds of individuals, often more severe than the general population with significant forefoot valgus 4
• Marfan syndrome includes hindfoot deformity (scored as 2 points) or plain pes planus (scored as 1 point) as part of the systemic scoring system 4
• Rheumatologic, neuromuscular, genetic, or collagen conditions can present with rigid pes planus requiring subspecialist referral 2

Adult Pes Planus Etiology

Posterior Tibial Tendon Dysfunction (Most Common)

• Posterior tibial tendon dysfunction (PTTD) is the most common cause of acquired pes planus in adults 2, 5
• Age-related tendon degeneration is a primary factor in PTTD development 5
• Inflammatory arthritis contributes to posterior tibial tendon weakening 5
• Metabolic factors including hypertension, diabetes mellitus, and obesity increase PTTD risk 5
• Peritendinous injections can precipitate tendon dysfunction 5
• Acute traumatic rupture of the posterior tibial tendon, though rare, can cause sudden-onset pes planus 5

Biomechanical Cascade

• The posterior tibial tendon is the primary dynamic stabilizer of the medial arch, providing plantar flexion and inversion while locking midtarsal joints 5
• When the tendon fails, other foot ligaments and joint capsules progressively weaken, leading to arch collapse 5
• A vicious cycle of deformity progression develops, with increasing plantar pressures in the midfoot perpetuating further tissue damage 6

Activity-Related Acquired Pes Planus

• Repetitive loading stress from high-impact activities like rucking, running, and marching causes posterior tibial tendon dysfunction in adults with pre-existing conditions or risk factors 6
• The biomechanical cascade from posterior tibial tendon weakness increases plantar pressures during walking and standing, perpetuating tissue damage 6
• Delayed treatment can lead to rigid, irreversible deformity and midfoot ulceration 6

Clinical Distinction: Flexible vs. Rigid

• Flexible pes planus demonstrates a normal arch during non-weight-bearing or tiptoeing, with flattening only on standing 2
• Rigid pes planus maintains a stiff, collapsed arch regardless of weight-bearing status and requires subspecialist referral 2

Associated Conditions

• Foot deformities such as hammer toes, mallet toes, claw toes, hallux valgus, prominent metatarsal heads, pes cavus, Charcot neuro-osteoarthropathy, or limited joint mobility can coexist with or contribute to pes planus 4
• Achilles tendinopathy is associated with anatomic deformities including excessive pes planus or foot pronation 4