Flat feet, also called pes planus, is a common orthopedic condition in which the inner arch of the foot is low or completely flattened. This condition may lead to pain, fatigue, and deformity in the foot over time. The foot’s primary functions are to support body weight and assist in forward motion. To accomplish this, the foot is composed of multiple small bones connected by ligaments and muscles that form arches to absorb shock and maintain stability.
Anatomy and Function of the Arch
The arches of the foot distribute body weight evenly and prevent compression of nerves and blood vessels on the inner side of the foot. The inner arch acts like a bridge, supported by the wedge-shaped bones of the midfoot. The plantar and spring ligaments act as staples holding these bones together, while the plantar fascia and intrinsic muscles function as tie-beams. The posterior tibial tendon, anterior tibial tendon, and deltoid ligament act as dynamic slings maintaining the height and stability of the arch during walking.
Types of Flat Feet
More than two-thirds of adults have flexible flat feet, where the arch collapses only during standing or weight-bearing but reappears when sitting or standing on tiptoes. Flexible flat feet are usually painless and may not require treatment. In contrast, rigid flat feet have a persistently absent arch in both weight-bearing and non–weight-bearing positions and are often associated with structural or neuromuscular abnormalities.
Causes
Flat feet may result from genetic, congenital, or acquired conditions.
Inherited connective tissue disorders such as Ehlers-Danlos syndrome, Marfan syndrome, Down syndrome, tarsal coalition, and congenital vertical talus are common causes. Acquired flatfoot may develop after arthritis (arthrosis), trauma, clubfoot treatment, or Achilles tendon contracture due to conditions like gout or rheumatoid arthritis. Neuromuscular conditions such as cerebral palsy may also cause rigid flatfoot deformities.
Symptoms
Most patients are initially asymptomatic but can develop pain, fatigue, and deformity over time. Common symptoms include:
- Pain and burning sensations in the foot, especially after prolonged standing or walking
- Clumsiness or altered gait, with the patient lifting the entire foot off the ground rather than rolling from heel to toe
- Tightness of the Achilles tendon, worsening deformity
- Development of secondary conditions such as Achilles tendonitis, plantar fasciitis, or bunions
Over time, untreated flat feet can result in joint stiffness and arthritis in the feet.
Diagnosis
Flat feet are normal in children under three years of age, as the arches usually develop by that time. The condition is most often diagnosed in adolescents or young adults. Diagnosis involves a thorough physical examination and evaluation of medical and family history. The foot is examined in both standing and non–weight-bearing positions to assess arch flexibility and Achilles tendon tightness.
Clinical tests are used to evaluate arch height and motion of the upper, mid, and lower foot. X-rays are performed to identify bony abnormalities, while CT scans can reveal fused tarsal bones. MRI may be used to assess tendons, ligaments, and other soft-tissue structures.
Management
Treatment depends on the type of flatfoot and the severity of symptoms.
- Flexible Flatfoot: Most cases are asymptomatic and require no intervention. Physical therapy and exercises that strengthen the foot muscles and stretch the Achilles tendon can help maintain arch integrity. Pain relief may be achieved with nonsteroidal anti-inflammatory drugs (NSAIDs). Arch supports, heel inserts, or custom orthotics can provide additional support and stability. Special braces may help realign the heel in symptomatic cases.
- Exercises: Exercises to strengthen the arch and foot muscles include picking up marbles with the toes, walking barefoot on sand, and toe-walking to stretch and strengthen the calf muscles.
- Surgical Treatment: Surgery is reserved for rigid flatfoot or flexible flatfoot with complications such as persistent pain or progressive deformity. Procedures may include lengthening of the Achilles tendon, cutting and realigning bones (osteotomy), fusing joints to stabilize the foot, or reconstructing tendons to restore arch height.
Prognosis
Most cases of flat feet are painless and do not require treatment. In symptomatic patients, conservative care is usually effective, and surgical correction can significantly relieve pain and restore function. Untreated rigid flatfoot or associated conditions like tarsal coalition may require surgical correction to maintain flexibility and prevent long-term deformity.
Prevention
Most cases of flat feet cannot be prevented, but wearing well-supported footwear and maintaining good strength and flexibility in the lower limbs can help minimize symptoms. Early intervention in children with abnormal gait or pain can prevent future complications.
Research Spotlight
A 2024 systematic review and meta-analysis published in the Journal of Biomechanics examined how foot orthoses (insoles) affect walking mechanics in adults with flexible flat feet.
After analyzing 24 studies, researchers found that orthotic use significantly reduced rearfoot eversion, ankle dorsiflexion, and knee adduction moments—key indicators of improved foot and leg alignment during walking. The review highlighted that studies using the Foot Posture Index (FPI-6) method showed the strongest biomechanical benefits, suggesting this standardized measure should guide future evaluations of flat-foot correction.
Overall, the findings reinforce the role of orthotics in improving lower limb function and gait efficiency in adults with flat feet. (“Study on the biomechanical effects of foot orthoses in adults with flat feet – see PubMed.”)
References / Citations (Optional)
Grear BJ. “Disorders of Tendons and Fascia and Adolescent and Adult Pes Planus.” Campbell’s Operative Orthopaedics. 14th ed. Elsevier; 2021.
Myerson MS, Kadakia AR. “Correction of Flatfoot Deformity in the Adult.” Reconstructive Foot and Ankle Surgery: Management of Complications. 3rd ed. Elsevier; 2019.
Winell JJ, Davidson RS. “The Foot and Toes.” Nelson Textbook of Pediatrics. 21st ed. Elsevier; 2020.
Orthobullets Team. “Adult Acquired Flatfoot Deformity.” Orthobullets. Updated October 9, 2025.
