What it is
The arch of the foot is held up by the shape of the bones, the ligaments that tie them together, and the tendons that run under and behind them. When the arch sits low, the heel tips outward and the front of the foot turns out. That combination is what "flatfoot" describes.
A low arch is not in itself a disease. It is a normal variant in a large part of the population, and most people who have one will never have a problem. What matters clinically is whether the foot is flexible or rigid, whether it hurts, and whether it is changing over time.
In children
Every small child looks flat-footed. The arch is filled with a fat pad, the ligaments are lax, and the bones have not finished forming. The arch appears on its own in most children between the ages of about four and ten.
A flexible, painless flatfoot in a child needs reassurance, not treatment. Insoles have been studied repeatedly and do not change the shape the foot ends up with.
Assessment is warranted when the flatfoot is:
- painful, particularly under the inner ankle or in the outer part of the hindfoot
- rigid, with no arch appearing on tiptoe
- one-sided, or clearly worse on one side
- associated with a tight calf, which drives the deformity and can often be treated on its own
- accompanied by clumsiness or worsening walking, which raises the question of an underlying neurological cause
In adults
An adult arch that was once normal and is now collapsing is a different problem. The usual cause is progressive failure of the posterior tibial tendon, the tendon that runs behind the inner ankle and lifts the arch with every step. It presents as pain and swelling on the inside of the ankle, an arch that is flattening, and increasing difficulty rising onto tiptoe on that leg.
This condition is progressive. Treated early, while the foot is still flexible, the options are simple and the results are good. Left for years, the hindfoot stiffens and the choices narrow to fusion. Early assessment genuinely changes the outcome.
How it is assessed
- Examination standing and walking, which is the part that matters most. A flatfoot cannot be assessed on a couch.
- The tiptoe test, to separate flexible from rigid.
- Calf tightness (Silfverskiold test), because a tight gastrocnemius is a common and correctable driver.
- Weight-bearing radiographs. Films taken lying down are of little use. Standing films let the alignment be measured, typically the Meary angle, calcaneal pitch, talonavicular coverage and Kite angle.
- MRI or CT only where a tendon tear, a coalition or arthritis is suspected.
Treatment without surgery
This is where most people start, and where most people stay.
- Calf stretching, done properly and for long enough. A tight calf forces the arch down at every step.
- Strengthening of the posterior tibial and intrinsic foot muscles.
- Supportive footwear, and an orthosis where it helps comfort.
- Activity and load management, and weight reduction where relevant.
- A period of immobilisation in a boot for an acutely inflamed tendon.
When surgery is considered
Surgery is for a foot that stays painful after a genuine trial of non-operative treatment, or a deformity that is clearly progressing. The operation is planned around what is actually wrong, and usually combines two or three of the following:
- Calf lengthening (gastrocnemius recession) where the calf is tight.
- Calcaneal osteotomy, cutting and shifting the heel bone back under the leg to restore alignment.
- Lateral column lengthening, to correct the outward rotation of the forefoot.
- Arthroereisis or a calcaneo-stop screw in the growing child: a small implant in the sinus tarsi that limits the collapse while the foot grows. It is minimally invasive and reversible, and the implant is usually removed later.
- Tendon transfer or repair, where the posterior tibial tendon has failed.
- Fusion, restricted to feet that are already rigid or arthritic.
The principle throughout is to correct the alignment while keeping the joints moving. Fusing a flexible foot solves the shape and creates a new problem.