A child with longitudinal cleavage of the upper extremity: treatment and etiology considerations.

We report a 4-year-old boy with a normal right upper extremity and 2 left upper extremities. These extremities included one with radial components including the radius and rudimentary thumb ray extended from the humerus in the more superior extremity, and another with the ulna and ulnar hand elements attached more inferiorly to the thorax. The patient had normal shoulder motion but no other function in the more superior extremity; the inferior extremity had active flexion and extension of the 2 fingers. We excised the nonfunctioning radius and thumb and performed an "on-top-plasty" by mobilizing the inferior extremity on its neurovascular pedicle and fusing the ulna to the distal aspect of the humerus of the superior extremity. This unusual clinical presentation may represent a proximal manifestation of central longitudinal deficiency with early limb bud cleavage affecting the apical ectodermal ridge and underlying mesoderm.