Modular joint prosthesis with a curved shaped head piece, on whose conical spike an insertable kneecap is fixed and with a nail (2) that can be housed in the medullary canal of the os longum (long bone) with a nail neck (7 ), being provided between the head part (1) and the nail neck (7) a connecting element, which holds the head part securing it against rotation, characterized in that the joining element includes at least one module (3, 3.1-3.4) as a sleeve, placed in the direction of the nail axis with at least two semi-bushes (8.1, 8.2) divided in the axial direction (LA) of the module (3, 3.1-3.4) and joined together such that they can be released, which form a pin (9) that extends axially to each other to insert the nail neck (7) into the pin (9) and the recesses (12.1, 12.2) coaxially arranged in the longitudinal direction of the module ( 3), positioned in each case perpendicular to the axis (LA) and that correspond to each other, to accommodate a fastener (16), which after fastening fixes the collar of the nail (7) on the pin (9) exclusively by dragging by means of a jaw with a sufficient torque against the axial displacement and rotation.Prótesis articular modular con una pieza de cabeza realizada con forma curvada, sobre cuya espiga cónica está fijada una rótula insertable y con un clavo (2) que puede alojarse en el canal medular del os longum (hueso largo) con un cuello del clavo (7), estando previsto entre la parte de cabeza (1) y el cuello del clavo (7) un elemento de unión, que sujeta la parte de cabeza asegurándola frente al giro, caracterizada porque el elemento de unión incluye al menos un módulo (3, 3.1-3.4) a modo de manguito, colocado en la dirección del eje del clavo con al menos dos semi-casquillos (8.1, 8.2) divididos en la dirección axial (LA) del módulo (3, 3.1-3.4) y unidos entre sí tal que pueden soltarse, que configuran entre sí un pasador (9) que se extiende axialmente para introducir el cuello del clavo (7) en el pasador (9) y las escota
