An implant assembly for a long bone is adapted to support an exo-prosthesis. The assembly includes a stem, a subdermal component and a percutaneous post. The stem has a proximal end that is adapted to be received in a surgically prepared medullary canal of the long bone, and a distal end having a surface that is adapted to promote bone ingrowth. The subdermal component includes a proximal portion that is adapted for attachment to the distal end of the stem, and a fixation surface that is adapted to promote soft tissue fixation. The percutaneous post has a proximal end that is adapted to be attached to the subdermal component.