A femoral prosthesis system is disclosed, which comprises:a femoral component (30) having a bone contacting side and an articular side, the articular side having a lateral and medial condyles； anda void filling prosthesis (10) having a central body (11) and lateral and medial legs (12, 13) connected to the central body and extending therefrom, the medial and lateral legs each having an outer surface having a frustoconical shape.
