A modular joint prosthesis includes a nail for insertion into a bone marrow canal, the nail having a nail neck. A neck piece has a proximal end, a middle shaft portion defining a longitudinal axis, and a distal end with a conical pin to which a slip-on joint ball can be attached. The proximal end of the neck piece has a helmet-shaped receiving head that includes an insertion opening for insertion of the nail neck or a module connector, a slot extending in the direction of the longitudinal axis, and corresponding recesses positioned on either side of the slot and extending perpendicularly to the longitudinal axis. The corresponding recesses receive a tensioning means which, in a tensioned state, clampingly fixes the nail neck or the module connector in the receiving head by frictional engagement in a jaw-like manner by application of tightening torque sufficient to prevent axial displacement and rotation.
