The invention relates to an endoprosthesis shaft system for elongate bones, comprising an anchoring part (10) and a shaft (1), which is formed from module elements that can be coupled by means of a plug-in connection (45), wherein a mutual rotation of the elements along the shaft (1) is adjustable and is blocked by means of an anti-rotation mechanism. In order to adjust the rotation, a rotation piece (5) is provided as a further module element, which has a self-contained rotation adjustment device (6) and a clamping device (7) as a mechanism for blocking the rotation. The rotation piece (5) comprises two end faces for the plug-in connection (45) and a sleeve (77). The invention provides, with the rotation piece, a particular module element for the shaft, which as a structural unit allows both an adjustment of the rotation and a blocking against undesired rotation in a self-contained unit.
