Flat foot (pes planus)

What is a flat foot?

In a flat foot the inner arch is low, so most of the sole touches the ground when standing. It can be flexible, where the arch reappears when you sit or stand on tiptoe, or rigid, where the arch stays flat.

What causes it?

Present from childhood

• Inherited foot shape. Many people have always had flat feet.
• Flexible flat foot, the most common type in children and adults, often without symptoms.
• Tarsal coalition. An abnormal bridge between two foot bones, often noticed in adolescence, which makes the foot stiff.

Developing in adulthood

• Tibialis posterior tendon dysfunction (progressive collapsing foot deformity). The most common cause in adults. The tendon that supports the arch becomes weakened or damaged and the arch gradually collapses. The spring ligament under the arch is often stretched too.
• Injury to tendons, ligaments or bones of the foot.
• Arthritis, including rheumatoid arthritis.
• Loose ligaments (hypermobility).
• Body weight, which increases load on the arch.
• Nerve or muscle conditions that cause weakness, and diabetic neuropathy.

What are the symptoms?

• Pain along the inside of the foot and ankle, sometimes with swelling
• Aching arches and tired feet after standing or walking
• Pain on the outside of the ankle as the heel drifts outwards in advanced cases
• Difficulty standing on tiptoe on one leg
• Knee, hip or back discomfort from altered alignment
• Shoes wearing unevenly

Treatment without surgery

• Insoles (orthotics). Arch supports, from off-the-shelf to custom-made, to support and realign the foot.
• Supportive footwear with a firm heel counter. Avoid flip-flops and flat, unsupportive shoes.
• Physiotherapy. Strengthening the tibialis posterior and calf, and stretching a tight calf.
• Activity changes, such as cycling or swimming instead of running.
• Pain relief and weight management.
• A brace or boot for a period in active tibialis posterior tendon problems.

Flat foot surgery

Surgery is for flat feet that remain painful or keep collapsing despite these measures. It is tailored to the cause and usually combines several procedures:

• Calf lengthening (gastrocnemius release) to reduce the pull that flattens the foot
• Tendon repair or transfer to replace a failing tibialis posterior tendon
• Spring ligament reconstruction to support the arch from below
• Osteotomy. Realigning bones, commonly moving the heel bone inwards, lengthening the outer foot or bringing the big toe side of the foot down
• Fusion of hindfoot joints when there is arthritis or a rigid deformity
• Subtalar arthroereisis, an implant to limit excessive rolling in, in selected cases