The invention relates to a tibial part of a knee prosthesis, having a tibial plateau and a tibial insert, two abutments distinct from each other, one anterior and one posterior, projecting from the upper face of the tibial plateau, the anterior abutment extending along at least part of the anterior margin of the tibial plateau, and the posterior abutment extending along at least part of the posterior margin of the tibial plateau and having a part forming a promontory (14； 14'； 14''), and an anterior and in particular central cut-out (11) in the form of a window being formed in the anterior abutment (4； 4') and opening out from the posterior face (7； 7') of the latter opposite the part (14； 14'； 14'') forming the promontory, the tibial insert having an upper face (23), a lower face (22) and a lateral face, the lateral face having an anterior face, a posterior face and two side faces, namely lateral and medial, a posterior cut-out (26； 26') open at the top and on the posterior side being formed in the lower face, the posterior cutout being delimited by an anterior face set back with respect to the posterior face of the insert and having a region with a shape complementing the part forming the promontory, characterized in that at least one elastic tab, in particular in the form of a hook, protrudes from the anterior face of the insert, in particular centrally, and penetrates in particular by a snap-fit action into the anterior cutout (11) in the form of the window.L'invention concerne une partie tibiale d'une prothèse de genou, comportant un plateau tibial et un insert tibial, deux butées distinctes l'une de l'autre, respectivement antérieure et postérieure, faisant saillie de la face supérieure du plateau tibial, la butée antérieure s'étendant le long d'au moins une partie du bord antérieur du plateau tibial et la butée postérieure s'étendant le long d'au moins une partie du bord postérieur du plateau tibial et comportant une partie formant promontoire (14； 14'；14''),
