Clasped thumb

Congenital clasped or clutched thumb is an anomaly where the metacarpal is held adducted and the interphalangeal joint flexed. It is normal for babies under the age of 4 months to clasp the thumb, however if symptoms persist beyond this time, differentials include congenital clasp thumb, trigger thumb, thumb hypoplasia or minor variant radial club hand.

Males are affected twice as frequently as females. Clasped thumb is associated with digitotalar syndrome and Freeman-Sheldon syndrome.

Clinical features can indicate the underlying anatomical problem:

• lack of extension at the interphalangeal joint: extensor pollicis longus absent
• lack of extension at the metacarpophalangeal joint: extensor pollicis brevis absent; thought to be the commonest form
• adduction across the palm: abductor pollicis longus absent

More than one of these three tendons may be absent or hypoplastic in the same thumb. Additionally, there may be inadequate skin laxity, joint contractures, lax collateral ligaments and absence of the extensor indicis proprius muscle.

Most children improve with splintage in extension. Surgical intervention is warranted if splintage fails after a trial period of at least three months. Surgery is dependent on the deficiency but can include web space deepening and tendon transfer to allow thumb extension using either extensor indicis proprius (EIP), extensor digiti minimi, extensor carpi ulnaris or flexor digitorum superficialis. As well as a deficiency of thumb tendons, EIP may also be absent in the same hand and as such, any surgical plan for reconstruction must have a reserve tendon option if EIP is found to be deficient on exploration.