Flatfeet, from paediatric arches to adult acquired flatfoot deformity.

Flatfeet - also called pes planus or fallen arches - describe a foot with a low or absent medial longitudinal arch. Many people have flexible flatfeet lifelong with no problems. Others develop adult acquired flatfoot deformity (AAFD, now called progressive collapsing foot deformity or PCFD), where the arch collapses over time, most often because the posterior tibial tendon and spring ligament fail.

Usually not. Paediatric flatfoot is nearly always physiological, painless and self-resolving as the foot matures. Reassurance and normal shoes are almost always enough. A painful, stiff flatfoot in an older child or adolescent - especially with peroneal spasm - is different and can suggest a tarsal coalition, which needs specialist assessment.

It is a progressive collapse of the medial arch in adults, most often due to posterior tibial tendon dysfunction with failure of the spring ligament, deltoid and midfoot supports. The Johnson and Strom stages, now updated by the Myerson consensus, describe how far the deformity has progressed - from tenosynovitis with a preserved arch, through flexible and then rigid deformity, to late ankle valgus.

By history and clinical examination - looking at gait, hindfoot alignment, the too-many-toes sign, single-heel raise and whether the arch reforms on tiptoe. Weight-bearing X-rays confirm the pattern. MRI or ultrasound of the posterior tibial tendon, spring ligament and deltoid is used when reconstruction is being planned.

For symptomatic flatfoot, first-line care is custom orthotics with medial arch and heel support, specialist foot and ankle physiotherapy (calf stretching, posterior tibial and intrinsic strengthening), analgesia and, in advanced cases, an Arizona brace or ankle-foot orthosis. Weight loss and activity modification are important. Selective image-guided injections may be used, but intra-tendinous steroid is avoided.

When pain and deformity persist despite good conservative care. Flexible painful deformity is usually treated with a medial displacement calcaneal osteotomy, flexor digitorum longus transfer and often lateral column lengthening (the Evans procedure). Rigid or arthritic deformity is treated with subtalar, talonavicular or triple arthrodesis. Late-stage disease with ankle valgus needs specialist ankle and hindfoot reconstruction.