has part has part characteristic of has modifier Duplication of the 1st metacarpal Bifid first metacarpal In contrast to the metacarpals 2-5, the first metacarpal is embryologically of phalangeal origin (equivalent to the proximal phalanges of the other digits). This term applies if the first metacarpal is partially duplicated. Depending on the severity the appearance on x-ray can vary from a notched metacarpal (the duplicated bone is almost completely fused with the metacarpal) to a partially fused appearance of the two bones. In most cases the fused bone resembles a Y-shape. Partial duplication of the proximal phalanges of the hand cleft abnormal metacarpal bone of digit 1