Continuing Education Activity

Pes planus is a common foot deformity characterized by partial or complete loss of the medial longitudinal arch during weight-bearing, with flexible and rigid subtypes. Congenital pes planus is common in early childhood and often resolves as the arch develops, whereas acquired pes planus most commonly results from posterior tibial tendon dysfunction, ligamentous laxity, obesity, trauma, or inflammatory or degenerative arthropathy. Clinical impact ranges from an incidental finding on examination to activity-limiting pain, altered gait mechanics, and progressive deformity affecting the ankle, knee, hip, and lumbar spine. Evaluation integrates focused history, weight-bearing and non–weight-bearing examination, assessment of hindfoot alignment and flexibility, and imaging when indicated. Weight-bearing radiographs support diagnosis and characterization of deformity, whereas advanced imaging may be used to assess tendon integrity, coalition, and arthritic changes.

Course participation builds competence in identifying flexible versus rigid flatfoot, recognizing key examination findings, and applying an evidence-informed diagnostic approach that includes appropriate selection and interpretation of imaging. Course participants learn to distinguish common mimics (eg, tarsal coalition, arthropathy, neuropathic collapse) and to individualize management based on etiology, symptom severity, and functional goals. Emphasis is placed on conservative strategies, including footwear modification, orthotics, activity modification, analgesic options, and rehabilitation targeting strength, flexibility, and proprioception, with escalation criteria for operative referral. Collaboration with an interprofessional team enhances symptom control, reduces complications, and improves functional outcomes.

Objectives:

• Compare weight-bearing and non–weight–bearing findings and correlate them with symptoms in the diagnosis of pes planus.
• Differentiate flexible versus rigid pes planus and common mimics.
• Select appropriate conservative therapies and criteria for advanced imaging or referral.
• Implement coordinated communication and collaboration among the interprofessional healthcare team to optimize outcomes.

Introduction

Pes planus, commonly referred to as flat feet, is a foot deformity defined by the loss of the medial longitudinal arch of the foot, with the arch contacting or nearly contacting the ground.[1] Pes planus can be congenital or acquired, and newborns are typically born with flat feet. The arch of the foot serves as an adaptive, flexible base and dissipates weight-bearing forces during the gait cycle.[2][3] Clinical and radiographic evaluation are necessary to determine the extent and flexibility of the deformity. Pes planus is often asymptomatic but may alter the biomechanics of the lower extremities and lumbar spine, increasing the risk of pain and injury to the foot, ankle, knees, and hips, and may necessitate conservative or surgical intervention.[4][5]

Etiology

Pes planus can either be congenital or acquired.

Congenital

Infants are usually born with flat feet, and children typically do not develop a normal arch until ages 7 to 10.[6] Infants and young children are prone to absent arches due to ligamentous laxity and limited neuromuscular control.[7] Infants have a fat pad under the medial longitudinal arch that protects the arch during early childhood.[8] Most cases of pes planus in children are flexible. Flexible pes planus describes a normal arch in the non–weight-bearing position that disappears with weight-bearing.[1] Some children do not develop a normal arch by adulthood. Pes planus is more prevalent among children who are overweight or obese,[9][10][11] with reported prevalences of 4% to 28%.[11][12]

Acquired

Acquired pes planus is most commonly secondary to posterior tibial tendon dysfunction. The tendon supports the arch and provides inversion and plantarflexion of the foot. Dysfunction can result from attenuation or stretching, tears, or ruptures. Previously, dysfunction was most commonly identified in women older than 55 with comorbidities, including diabetes mellitus and obesity;[9] more recent epidemiologic data suggest a broader distribution, corresponding with rates of obesity.

Patients with trauma to the midfoot or hindfoot resulting in navicular, first metatarsal, calcaneal, or Lisfranc ligament complex demonstrate an increased risk of developing pes planus.[10][11] Other causes include injuries to soft tissues such as the plantar fascia or spring ligament.[12][13] Patients with sensory neuropathy may experience Charcot arthropathy, leading to midfoot collapse over time.[14]

Patients with congenital ligamentous laxity secondary to Down syndrome, Marfan syndrome, or Ehlers-Danlos syndrome can present with pes planus.[15][16][17] Ligamentous laxity secondary to pregnancy may also cause pes planus, but it typically resolves postpartum.[18] Patients with arthropathies are at higher risk for acquired pes planus due to degenerative or inflammatory conditions. Patients with rheumatoid arthritis or seronegative arthropathies are at higher risk for pes planus, especially if their disease is poorly controlled.[19]

Epidemiology

Approximately 20% to 37% of the population is estimated to have some degree of pes planus.[20][21][22] Most cases are flexible pes planus. Results from a 2003 study by Dunn et al found that the prevalence among non-Hispanic White individuals was 17% and was higher among Black individuals (34%).[23] 

A 2023 study by Salinas-Torres reviewed 12 studies, including 2509 feet with pes planus; the results showed the highest incidence among men, children aged 3 to 5 and 11 to 17 years, Asian individuals, and individuals with obesity. Furthermore, incidence was lower in women and in White populations. Although this study's results found a lower incidence of pes planus among females, results from other studies have reported a 3-fold higher prevalence among females.[9][24] Pes planus is more common in children, but most develop a normal arch by age 10 years. This condition has a strong genetic and familial component.[25] Finally, the radiographic or clinical presence of pes planus may be an incidental finding in patients and requires clinical correlation.

Pathophysiology

The medial longitudinal arch comprises the calcaneus, navicular, talus, first 3 cuneiforms, and first, second, and third metatarsals.[26] The arch is supported by the spring ligament (plantar calcaneonavicular ligament), deltoid ligament, posterior tibial tendon, plantar aponeurosis, and the flexor hallucis longus and brevis muscles. Dysfunction of any portion of the medial longitudinal arch may result in acquired pes planus.

The main factors that contribute to an acquired flat foot deformity are excessive tension in the triceps surae, obesity, posterior tibial tendon dysfunction, or ligamentous laxity in the spring ligament, plantar fascia, or other supporting plantar ligaments.[27] Pes planus may also result from tightness of the Achilles tendon or calf muscles.[28] Rigid pes planus is rare and typically develops during childhood, but may occur at any age. This condition may result from the tarsal coalition, accessory navicular bone, congenital vertical talus, or other forms of congenital hindfoot pathology.

History and Physical

The physical examination should consist of inspection, palpation, range of motion, muscle strength testing, and gait assessment. Findings should be compared with those of the contralateral extremity.

• Inspection: The examiner should evaluate the patient in both weight-bearing and non–weight-bearing positions. Pes planus is often apparent on inspection. In flexible pes planus, an arch is present in the non–weight-bearing position but disappears with weight-bearing. The patient may also overpronate. Viewing the patient from behind may demonstrate the too many toes sign and calcaneal valgus. Please see StatPearls' companion topic, "Posterior Tibial Tendon Dysfunction," for further information. Both feet should be compared for asymmetry. Patients with pes planus may also have a bunion deformity and possibly hammertoe formation.[29] (See Image. Pes Planus Examination.)
• Palpation: The examiner should palpate the posterior tibial tendon, lateral rearfoot, and plantar fascia, and subtalar joint. Pain may be elicited in any of these anatomic locations, including the early stages of pes planus.
• Range of motion: Range-of-motion testing helps distinguish flexible from rigid pes planus. Flexibility can also be assessed using the Hubscher maneuver (Jack test) to determine if the deformity is reducible. Subtalar joint range-of-motion testing can help distinguish a tarsal coalition from secondary osteoarthritis in a pes planus foot. Pain or restricted motion on any of these examinations, in the presence of confirmed or suspected pes planus, may require further diagnostic studies.
• Muscle strength testing: The examiner can evaluate muscle strength by having the patient perform single- and double-toe raises. Posterior tibial tendon strength can be assessed by having the patient invert the foot against resistance.[30] Pain along the posterior tibial tendon or inability to perform the toe raise examination may suggest dysfunction of the posterior tibial tendon associated with pes planus.
• Gait assessment: The patient may have an antalgic gait. Examiners may observe overpronation, along with compensatory knee and hip mechanics during ambulation.

Evaluation

Plain Radiographs

Three standard weight-bearing radiographs of the feet (lateral, dorsoplantar [anteroposterior], and medial oblique views) are often sufficient for diagnosis. Additional radiographic views, such as a calcaneal axial, may be obtained as indicated. 

Lateral weight-bearing radiographs

On lateral weight-bearing radiographs, the following findings are often noted:

• Meary angle (talo-first metatarsal angle): Measures the talar axis to the first metatarsal axis by drawing a line from the center longitudinal axis of the talus to the first metatarsal. A normal finding is approximately 0°, and in a rectus foot, the angle should be contiguous. A downward apex greater than 4º indicates longitudinal arch collapse at the talonavicular joint.
• Talar declination angle: Measures the talus tilt in comparison to the weight-bearing surface. In a flat foot, the talus is usually plantarflexed (pointing towards the weight-bearing surface). Although threshold values vary, an angle greater than 24° is generally indicative of pes planus.
• Calcaneal inclination angle: A calcaneal inclination angle of less than 18° indicates pes planus. This angle is obtained from the calcaneal inclination axis (line between the most inferior portion of the plantar and posterior calcaneus and the most distal and plantar portion of the calcaneal anterior process) and the horizontal surface on which the foot is placed.
• Cyma line: The cyma line is a lazy S-shaped line visualized on lateral and dorsal plantar radiographs between the talonavicular joint and calcaneocuboid joint. In pes planus, there is a break in the line. (See Image. Lateral Radiograph of Pes Planus.)

Medial oblique weight-bearing radiographs

On medial oblique weight-bearing radiographs, the following findings may be noted in pes planus secondary to a calcaneonavicular coalition:

• A close approximation or a physical osseous bridge between the anterior process of the calcaneus and the lateral portion of the navicular is suggestive of a coalition. (See Image. Medial Oblique View of Foot, Radiograph.)

Dorsoplantar (anteroposterior weight-bearing radiographs)

On dorsoplantar weight-bearing radiographs, the following findings are often noted:

• Calcaneocuboid angle: Measures the alignment between the lateral calcaneus and lateral cuboid, with a reference range from 0° to 5°. Measurements greater than 5° indicate an abducted forefoot on the rearfoot.
• Talar head uncovering: A measure of the medial talar head coverage by the associated navicular articulation. The navicular covers typically cover more than 75% of the talus. Uncovering greater than 30% is indicative of talar head rotation medially and often can be palpated in the severe pes planus foot.
• Kite angle (talocalcaneal angle): Measures the angle between the long axis of the talus and calcaneus. In a rectus foot, the talar axis should sit just medial to the first metatarsal, and the calcaneal axis should pass through the base of the fourth metatarsal. The reference range is typically 25° to 40°; in pes planus, the angle exceeds 40°. (See Image. Dorsal Plantar Radiograph of Pes Planus.)

Magnetic Resonance Imaging

MRI is often used preoperatively to assess the integrity of both soft-tissue and osseous structures. About soft tissue, the study can identify posterior tibial tendon dysfunction or injury to the spring ligament or other supporting soft-tissue structures. In assessing osseous structures, MRI can reveal osteoarthritic changes, avascular necrosis, cystic changes, and tarsal coalition. Edema at the plantar fascial calcaneal enthesis may support the diagnosis of plantar fasciopathy in the setting of heel pain.

Electromyography/Nerve Conduction Study

Electromyography and nerve conduction studies can be performed to evaluate for underlying sensory neuropathy.

Treatment / Management

Children

Children rarely require surgical intervention for pes planus. Foot orthotics are often the first-line treatment for foot pain secondary to pes planus, alone or in combination with leg, knee, and back pain.[31] Surgery may be indicated for rigid pes planus, tarsal coalitions, and progressive, symptomatic pes planus.[32]

Adults

In adults, treatment is based on the underlying etiology. Foot orthotics, appropriate and comfortable footwear, and nonsteroidal anti-inflammatory drugs are first-line therapies for pain.[33] Patients with obesity should be counseled regarding weight loss. For posterior tibial tendon dysfunction, treatment initially consists of rest, ice, nonsteroidal anti-inflammatory drugs, and immobilization. Physical therapy may help minimize pain, increase foot flexibility, strengthen weak muscles, and train proprioception. Surgical procedures are reserved for patients who do not improve with conservative measures.[1][34]

Surgical Procedures

In general, operative management of pes planus may include gastrocnemius resection in conjunction with osseous procedures, depending on patient symptoms and the severity of the deformity. In cases of rigid deformity, fusion of the rear and midfoot is usually performed. Procedures include subtalar joint fusion, talonavicular fusion, and calcaneocuboid fusion.

In pediatric individuals, special consideration must be given to open growth plates and to the need to avoid premature physeal closure, which can result in limb-length discrepancy. In flexible pes planus, procedures such as subtalar joint arthroereisis, Evans lateral column lengthening, Cotton osteotomy, first metatarsal cuneiform fusion, and medial calcaneal slide osteotomy (Koutsogiannis procedure) have been frequently employed, with high success and satisfaction rates.[35][36] More recently, attention has shifted to the deltoid ligament complex and its repair, as well as to other soft-tissue adjunct procedures.[37]

Differential Diagnosis

Pes planus has primary and secondary causes, and some presentations can mimic pes planus. Differential diagnosis is often limited to the following and can be excluded based on clinical evaluation and imaging studies:

• Posterior tibial tendonitis (often a contributing factor to the development of pain associated with pes planus)
• Tarsal coalition
• Arthritis (primary or secondary)
• Connective tissue disorders (eg, Marfan syndrome)
• Charcot arthropathy

Treatment Planning

Conservative treatment should continue for 2 to 3 months before consideration of surgical intervention. Before surgical intervention, more advanced imaging may be necessary to determine the extent of deformity. 

Prognosis

Pes planus is a multifactorial entity. Prognosis varies with the etiology, duration of symptoms, and treatment course. Degenerative and inflammatory arthritis, as well as Charcot arthropathy, are often difficult to treat and are associated with progressive symptom worsening over time. Surgical treatment for pathologies such as posterior tibial tendon tear, gastrocnemius tightness, or Achilles tendon contracture is associated with a favorable prognosis.[34] Activity modification for patients performing high-impact activities can also support conservative treatment.

Complications

Postoperative complications depend on the particular surgical procedure involved and include:

• Surgical site infection
• Malunion/nonunion
• Persistent pain
• Implant dislocation/fracture
• Other hardware complications
• Recurrence
• Progressive arthritis [34]

 Advanced deformities are associated with higher postoperative failure rates.[38]

Postoperative and Rehabilitation Care

Following surgical intervention, most patients are advised to use a protective non–weight-bearing brace for 6 to 8 weeks; total healing time is patient-dependent and may be prolonged by postoperative physical therapy, transitions of care, overall health status, and age. Patients often require a custom orthotic postoperatively to support the long-term outcomes of surgical intervention.

Deterrence and Patient Education

Patient education should focus on modifiable risk factors for pes planus. These include:

• Obesity with an emphasis on weight loss
• Diabetes mellitus with optimization of glycemic control to reduce the risk of sensory neuropathy and Charcot arthropathy
• Limitations on activities for those engaging in high-impact repetitive trauma [39]

Patients should also be counseled on the importance of adhering to the prescribed orthotic device. Please see StatPearls' companion resource, "Progressive Collapsing Foot Deformity," for further information.[39] Patients should be advised regarding expected postoperative pain and have a detailed plan for pain control. 

Pearls and Other Issues

The following are pearls regarding pes planus:

• Pes planus is a common finding on clinical examination and may be incidental.
• Pes planus can be acquired or congenital.
• Treatment is often nonsurgical and may require modification of footwear and orthotics.

Enhancing Healthcare Team Outcomes

Pes planus is best managed by an interprofessional team that includes physical therapists, primary care clinicians (for medical optimization), nurses, and postoperative support services. Surgical intervention should be reserved for the progressive, refractory pes planus that does not respond to conservative measures. Foot orthotics are indicated for foot pain secondary to pes planus alone or in combination with leg, knee, and back pain. Most patients achieve acceptable outcomes with orthotics alone; however, numerous advances in surgical technique have led to improved patient-reported outcomes and satisfaction with surgical intervention. 

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Disclosure: Josh Moore declares no relevant financial relationships with ineligible companies.

Disclosure: Dawood Tafti declares no relevant financial relationships with ineligible companies.