A modular endoprosthetic radial head implant includes an end cap secured to a cannulated body held to bone by a fixation element. The fixation element supports the cannulated body on a resected radial bone end, for example. The fixation element of one embodiment features a threaded stem with a spherical head. The stem fits distally into the cannulated body and extends through a hole formed by the distal end of the cannulated body. The spherical head nests inside the cannulated body. Polyaxial alignment between the cannulated body and the fixation element is locked using a jam nut tightened inside the cannulated body. An end cap fits into place proximally on the cannulated body. The end cap is formed of a joint surface material to provide a bearing surface.