A provisional tibial prosthesis system (30A, 30B) for a prosthetic knee joint for implantation in a natural knee, the provisional tibial prosthesis system is able to alternately mimic the geometry of a first final tibial prosthesis and a second final tibial prosthesis , the natural knee comprising a proximal tibia and a distal femur and having a medial / lateral axis (AML), an anterior / posterior axis (AAP) and a proximal / distal axis (APD), the medial / lateral axis corresponding to a medial / lateral direction (22), the anterior / posterior axis corresponding to an anterior / posterior direction (20) and the proximal / distal axis corresponding to a proximal / distal direction (24), the provisional tibial prosthesis system comprising: a tibial base plate (38A, 38B) having a bone contact surface (152A, 152B) and an upper surface (150A, 150B) of opposite base plate； a tibial bearing component having a tibial bearing component height, said tibial bearing component (32A, 32B) being attached to said tibial base plate, said tibial bearing component height representing the first final tibial prosthesis； and a wedge (36A, 36B) having a wedge height, the provisional tibial prosthesis system being configured such that said wedge is slidable with respect to said tibial base plate (38A, 38B) and said component (32A, 32B ) of the tibial bearing, so that it can be slidably received between said tibial base plate and said tibial bearing component in the anterior / posterior direction when said tibial base plate and said tibial bearing component are separated by a distance along of the proximal / distal axis equal to said wedge height and when the tibial prosthesis system is used in implantation in the natural knee, said wedge height cooperating with said height of the tibial bearing component to represent the second final tibial prosthesis； characterized in that said system further comprises: a base component (34A, 34B) configured to join with said tibial bearing component by
