Failure to differentiate occurs when the embryonic homogenous analog fails to separate. The most common type is syndactyly, in which the fingers are joined. Symphalangism is failure of the PIP joints to separate, resulting in immobile, often fused joints. Camptodactyly is curving with flexion contracture of the little fingers. Clinodactyly is angular deformity of the digits, which may occur in Down syndrome.
Duplication causes polydactyly.
The extra digits may be associated with any finger, but most commonly with the thumb or little finger. Duplication can involve larger segments or even the whole limb. Syndactyly with undergrowth is referred to as brachysyndactyly. Congenital constriction band syndrome involves circumferential constriction of the limbs. This deformation is likely caused by amniotic bands and may result in amputation of the distal portion.