SN6 SHORT NOTE 5M

Flat Foot

General Surgery · Final Professional

Definition

Flat foot (pes planus) is a loss of the medial longitudinal arch so that the sole appears flat and the hindfoot is in valgus. In children it is usually flexible and physiological; the crucial distinction is between a flexible flat foot (arch restored when non-weight-bearing) and a rigid flat foot (arch absent in all positions), which suggests underlying pathology.

Flexible VS Rigid

Flexible flat foot — common, usually asymptomatic, the arch reappears on tiptoeing or great-toe dorsiflexion (Jack’s test) and when the foot hangs free. It is a normal variant needing only reassurance. Rigid flat foot — the arch does not reform; causes include a tarsal coalition (an abnormal bony/fibrous bridge, often presenting with a painful ‘peroneal spastic’ flat foot in older children), congenital vertical talus, or inflammatory/neurological disease.

CLINICAL PEARL

The key clinical test: if the arch reforms on tiptoe (or with Jack’s test), the flat foot is flexible and benign; if it stays flat, it is rigid and warrants investigation for a tarsal coalition or other cause.

Management

Flexible, painless flat feet need only reassurance — no orthoses or special shoes are required to ‘create’ an arch. Symptomatic flexible flat feet may benefit from arch supports, stretching and supportive footwear. Rigid or painful flat feet are investigated (radiographs, CT for coalition) and treated according to the cause, occasionally surgically (e.g. Resection of a symptomatic coalition).

Tarsal Coalition

Tarsal coalition — an abnormal bony, cartilaginous or fibrous bridge between tarsal bones (commonly calcaneonavicular or talocalcaneal) — is the classic cause of a rigid, painful (‘peroneal spastic’) flat foot that becomes symptomatic in later childhood or adolescence as the bridge ossifies and restricts subtalar movement. It is confirmed on oblique radiographs or CT and treated first conservatively (orthoses, activity modification, immobilisation for flares) and, if that fails, by surgical resection of the coalition or, in advanced cases, arthrodesis.

CLINICAL PEARL

One test settles most cases: if the arch reappears on tiptoe (or Jack’s test), the flat foot is flexible and benign and needs only reassurance; a foot that stays flat in every position is rigid and warrants a search for a tarsal coalition or other cause.

The tiptoe test separates flexible from rigid flat foot.

KEY POINT

Key points TO remember

Loss of the medial longitudinal arch; usually flexible & physiological in children.
Flexible: arch reforms on tiptoe/Jack’s test — reassure; rigid: arch fixed — investigate.
Rigid causes: tarsal coalition, congenital vertical talus, inflammatory/neurological disease.
Painless flexible feet need no treatment; treat symptomatic/rigid feet by cause.

EXAM TIP

Sources: Maheshwari's Essential Orthopaedics; Apley & Solomon's System of Orthopaedics and Trauma; AO Principles of Fracture Management.

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