A modular knee prosthesis system, comprising: a distal femoral implant component having a pair of spaced, curved distal condylar surfaces (12, 14) and a stem having an outer surface tapering from a distal end in a proximal direction, the outer surface of the stem having a maximum outer diameter at the distal end and a smaller outer diameter at a second position proximal to the distal end, a proximal tibial implant component (30, 32) having an articulating surface (37, 39) to receive and articulate with the distal condylar surfaces of the distal femoral implant component, a first metaphyseal member having an outer surface that tapers in the proximal direction and an inner surface defining a tapered bore (68, 72), the outer surface of the first metaphyseal member comprising a stepped portion having a plurality of steps, each step having a maximum medial-lateral dimension and a maximum anterior-posterior dimension, the stepped portion having an overall axial length L, and a second metaphyseal member having an outer surface that tapers in the proximal direction and an inner surface defining a tapered bore (68A, 72A), the outer surface of the second metaphyseal member comprising a stepped portion having a plurality of steps, each step having a maximum medial-lateral dimension and a maximum anterior-posterior dimension, the stepped portion having an overall axial length L+X, characterised in that the proximal tibial implant component has a stem whose outer surface tapers from a proximal end in the distal direction, the outer surface of the stem having a maximum outer diameter at the proximal end and a smaller outer diameter at a second position distal to the proximal end, the tapered bore in each of the first and second metaphyseal members is sized and shaped to be mountable on the stem of one of the implant components to create a frictional lock between the stem and the member, and the maximum medial-lateral dimension and maximum anterior-posterior dimension of each step over the axial length L of the stepped portion of the second metaphyseal member is the same as the maximum medial-lateral dimension and maximum anterior-posterior dimension of each step over the axial length L of the stepped portion of the first metaphyseal member so that the same prepared bone space will receive either the first metaphyseal member or the second metaphyseal member. a distal femoral implant component having a pair of spaced, curved distal condylar surfaces (12, 14) and a stem having an outer surface tapering from a distal end in a proximal direction, the outer surface of the stem having a maximum outer diameter at the distal end and a smaller outer diameter at a second position proximal to the distal end, a proximal tibial implant component (30, 32) having an articulating surface (37, 39) to receive and articulate with the distal condylar surfaces of the distal femoral implant component, a first metaphyseal member having an outer surface that tapers in the proximal direction and an inner surface defining a tapered bore (68, 72), the outer surface of the first metaphyseal member comprising a stepped portion having a plurality of steps, each step having a maximum medial-lateral dimension and a maximum anterior-posterior dimension, the stepped portion having an overall axial length L, and a second metaphyseal member having an outer surface that tapers in the proximal direction and an inner surface defining a tapered bore (68A, 72A), the outer surface of the second metaphyseal member comprising a stepped portion having a plurality of steps, each step having a maximum medial-lateral dimension and a maximum anterior-posterior dimension, the stepped portion having an overall axial length L+X, characterised in that the proximal tibial implant component has a stem whose outer surface tapers from a proximal end in the distal direction, the outer surface of the stem having a maximum outer diameter at the proximal end and a smaller outer diameter at a second position distal to the proximal end, the tapered bore in each of the first and second metaphyseal members is sized and shaped to be mountable on the stem of one of the implant components to create a frictional lock between the stem and the member, and the maximum medial-lateral dimension and maximum anterior-posterior dimension of each step over the axial length L of the stepped portion of the second metaphyseal member is the same as the maximum medial-lateral dimension and maximum anterior-posterior dimension of each step over the axial length L of the stepped portion of the first metaphyseal member so that the same prepared bone space will receive either the first metaphyseal member or the second metaphyseal member.