Femoral head arthroplasty system

A kit comprising:

• a femoral prosthesis comprising:
• a mounting plate having a first side and an opposed second side, wherein the first side of the mounting plate is configured to abut a cut proximal end of a neck of a femur, wherein the mounting plate defines a threaded opening that is configured to receive a first thread defined by a head of a screw;
• an adapter extending from the second side of the mounting plate;
• and an implant body extending perpendicularly from the first side of the mounting plate, wherein the implant body extends from the mounting plate by a distance no greater than 90 mm, wherein the implant body has a centerline that is perpendicular to the first side of the mounting plate, wherein the implant body is oblong in cross section in the plane that is perpendicular to the first axis, wherein the implant body has a distal end, wherein the implant body defines a continuous, uninterrupted circumferential surface extending from the mounting plate to the distal end, wherein the continuous, uninterrupted circumferential surface comprises two hemi-cylindrical surfaces having respective lengths, the two hemi-cylindrical surfaces being spaced along the second axis, and two parallel planar faces that are spaced along the third axis and extend between and to the two hemi-cylindrical surfaces along a respective entirety of each of the lengths of the two hemi-cylindrical surfaces;
• and a plurality of femoral head replacements, each femoral head replacement having a generally spherical surface and comprising a recess that is shaped to complementarily receive the adapter of the femoral prosthesis, wherein each femoral head replacement of the plurality of femoral head replacements differs from every other femoral head replacement of the plurality of femoral head replacements in size or material.