The present invention regards a modular spacer device (1) for a knee joint comprising at least one tibial element (2) adapted to be constrained to the tibial bone, at one end of such bone facing the knee joint, and at least one femoral element (3), in turn adapted to be constrained to the femoral bone, at one end thereof facing the knee joint, and articulated on such tibial element (2). The tibial element (2) comprises a first surface (21) facing, during use, the femoral element (3) and a second surface (22) opposite thereto, and the femoral element (3) has a first surface (31) facing, during use, the tibial element (3), and a second surface (32) opposite thereto. The first surface (31) of the femoral element (3) is convex and laterally has a curved contour of "ammonite" type with curvature radius increasing starting from at least one rear section (PS) with curvature radius (R1), at least one first central section (FCS) with curvature radius (R2), at least one second central section (SCS) with curvature radius (R3), up to at least one front section (FS) of said femoral component (3) having curvature radius (R4), with R1≤R2≤R3≤R4.L'invention porte sur un dispositif d'espacement modulaire (1), pour l'articulation du genou, comprenant un élément (2) de contrainte du tibia, l'extrémité faisant face à l'articulation du genou, et un élément de contrainte du fémur (3), dont l'extrémité faisant face à l'articulation du genou, articulé sur l'élément de contrainte du tibia (2). L'élément de contrainte du tibia (2) a une première surface (21) tournée, lors de l'utilisation, vers l'élément de contrainte du fémur (3), et une seconde surface (22) opposée à celle-ci. L'élément de contrainte fémoral (3) a une première surface (31) tournée, lors de l'utilisation, vers l'élément tibial (3), et une seconde surface (32) opposée à celle-ci. La première surface (31) de l'élément fémoral (3) est convexe et a un contour courbe latéral de type "ammonite", dont le rayon de courbure augmente
