A joint prosthesis comprises a distal component for anchoring to a first bone, a proximal component for anchoring to a second bone, and a coupling piece that, together with the first component, forms a flexion bearing around a first axis and, together with the second component, forms a rotary bearing formed by the pin and the bearing bush around a second axis oriented transversely to the first axis. The rotary bearing comprises a multi-layer bearing insert, having a sliding sleeve surrounding the pin and a support sleeve that encloses said sliding sleeve and is fastened to the coupling piece by means of a securing element, wherein the securing element comprises an actuation unit within the support sleeve and can be connected to the coupling piece such as to ensure tensile strength by means of two aligned bores in the support sleeve and the coupling piece.