SN7 SHORT NOTE 5M

Define Achondroplasia. Describe its clinical features and management.

General Surgery · Final Professional

Definition

Achondroplasia is the commonest form of short-limbed (disproportionate) dwarfism. It is an autosomal-dominant disorder (most cases arising as new mutations, associated with advanced paternal age) caused by a mutation in the FGFR3 gene that inhibits endochondral ossification at the growth plate — so the long bones, which grow by endochondral ossification, are short, while membranous bone growth is relatively normal.

Clinical Features

There is disproportionate short stature with short proximal (rhizomelic) limbs, a relatively normal-length trunk, and a large head with frontal bossing and midface hypoplasia. The hands show a ‘trident’ configuration, and there is often genu varum and an exaggerated lumbar lordosis. Intelligence and life expectancy are usually normal.

DANGER / REMEMBER

Foramen magnum and spinal stenosis are important complications of achondroplasia: foramen magnum narrowing can cause cord/brainstem compression (and even sudden death) in infants, and lumbar canal stenosis commonly causes symptoms in adults — both may need surgical decompression.

Management

Management is supportive and multidisciplinary: monitoring growth and development, anticipating and treating complications (foramen magnum stenosis, spinal stenosis, hydrocephalus, recurrent otitis media, genu varum), and orthopaedic correction of deformity or decompression of stenosis as needed. Genetic counselling is provided; targeted therapies (FGFR3-pathway agents) are emerging.

Genetics & Inheritance

Achondroplasia is autosomal dominant, but around 80% of cases are new (sporadic) mutations in the FGFR3 gene, associated with advanced paternal age; an affected parent has a 50% chance of transmitting it. The FGFR3 mutation is a gain-of-function change that over-inhibits chondrocyte proliferation at the growth plate, restricting the endochondral bone growth responsible for long-bone length while sparing membranous (skull vault) growth, which explains the disproportionate phenotype.

CLINICAL PEARL

Recognise achondroplasia by rhizomelic (proximal) limb shortening with a normal-length trunk, frontal bossing and midface hypoplasia in a child of normal intelligence — and stay alert to foramen magnum and spinal canal stenosis, the complications that actually cause harm.

Membranous ossification is normal, so the skull vault and trunk are spared.

KEY POINT

Key points TO remember

Commonest short-limbed dwarfism; AD, FGFR3 mutation impairing endochondral ossification.
Rhizomelic short limbs, normal trunk, frontal bossing, midface hypoplasia, trident hand.
Normal intelligence & lifespan; watch for foramen magnum & spinal (canal) stenosis.
Supportive multidisciplinary care; decompress stenosis and correct deformity as needed.

EXAM TIP

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

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