The invention relates to a base that includes a unit for osseous attachment onto a tibia, and a plate having posterior, anterior, medial and lateral edges a posterior pin and an anterior pin having a posterior flat section and an anterior flat section two posterior lugs protruding above the plate and arranged on the posterior edge of each side of the posterior pin and two anterior lugs arranged on each side of the anterior pin. The posterior flat section and the anterior flat section are arranged so as to simultaneously engage with the insert. Each posterior tab includes a support extension for inserting, in an anteroposterior direction, a complementary support tab of the insert. Each anterior lug includes a unit for snap-coupling the insert onto the base.
