Bilateral extra tarsal bones in Rubinstein-Taybi syndrome: the fourth cuneiform bones

Rubinstein-Taybi syndrome is a syndrome of mental retardation associated wi th digital changes, consisting mainly of broad thumbs and large toes. This paper deals wit pedal changes in a patient with this syndrome in whom bilat eral, large, extra tarsal bones occurred between the medial cuneiform and i ntermediate cuneiform bones. They articulated with these bones, as well as with the first and the second metatarsals. It is suggested that these extra tarsal bones be labelled as the fourth cuneiform bones (os cuneiformis IV) . To the best of the author's knowledge, such an extra tarsal bone has neve r been reported in humans or other mammalians. One could speculate that the y originated from bilateral extra ossification centers or from an isolated, accelerated ossification and extreme enlargement of the so-called os inter cuneiforme, a supernumerary ossicle, in this patient with Rubinstein-Taybi syndrome.