The invention is generally directed to the novel and unique modular implant that provides an improved surface for interfacing with an external prosthesis. The implant includes a stem, an optional extension member connected to the stem, a prosthetic condyle, or in the case of application to other levels of cut bone amputations, a location-specific terminal shape, connected to the extension member. The stem is inserted directly into the canal of the bone and tissue, including muscle, is attached directly to the prosthetic and the stem is inserted directly into the canal of the bone. The simulated anatomically correct condyle better distributes the load of the patient's weight and avoids twisting thereby relieving pain to improve the functional connection between the residual limb and an external prosthesis in all levels of upper and lower extremity amputations. The surgically implanted internal prosthetic simplifies and lowers the cost of rehabilitation and results in an improvement in the function of all existing external prosthetic components and systems.