The invention presents a total knee arthroplasty endoprosthesis having: a) a femoral component with a lower-radius lateral condyle, a larger-radius medial condyle and between them, a third condyle located posteriorly, superiorly and nearest the medial side, b) a tibial component with a central protruding spigot for the rotating polyethylene insert, and c) a rotating polyethylene insert, with three cavities for articulation of the femoral condyles. For initial and moderate flexion the joint functions with load bearing onto the lateral and medial articular cavities, and in advanced and final flexion with load bearing on the third articular cavity. The advantages of this endoprosthesis are enhanced maximum flexion, improved femoral axis alignment, significant posterior stabilization, favourable accommodation of tibial rotation with consequent relief of materials and fixations, and preservation of more articular fluid for lubrication and reduction of polyethylene wear.