Syndactyly type 5 (SD5) is a very rare congenital limb malformation characterized by postaxial syndactyly of hands and feet, associated with metacarpal and metatarsal fusion of fourth and fifth digits.

Fusion involving two or more metacarpal bones (A synostosis of the first metacarpal and the proximal phalanx of the thumb can also be observed, note that the first metacarpal bone corresponds to a proximal phalanx).