The total knee prosthesis has a tibial section with a tibial plateau and a femoral section with a tibial insert between the tibial and femoral sections. The tibial insert has a base (5) and a movable tibial lug (6) extending perpendicular to the base. The lug has a pin (12) depending from its lower surface of greater length than the base thickness. The lug cannot pivot with respect to the base on the axis of the pin. Claims include a set of tibial inserts used for claimed prostheses.