An intramedullary nail for a fractured elongated bone, comprising a cannulated rod having proximal and distal ends; an outside tubular sleeve for coaxially hosting and guiding the rod; and at least a pair of shape memory elements hosted in corresponding seats at the distal end of the rod. Each shape memory element can be retractably housed in its seat in a first configuration, allowing insertion of the nail into the bone, and can project from a sleeve opening in another configuration. Pairs of transversal holes are provided in proximal portions of the rod and the sleeve. The distal pair of shape memory elements lie on an offset plane to the plane of the proximal holes and are kept in their corresponding seats by a distal cover fixed to the rod. This improves the stability of the nail in the medullary canal.