A prosthesis system (100) of the present invention includes a monoblock stem extension (10) comprising a proximal portion (20) having a first neutral axis (20a)； and a distal portion (30) defined by a longitudinal cylindrical shaft (31) having a. second neutral axis (30a), wherein the second neutral axis (30a) is parallel and offset by a distance a from the first neutral axis (20a): and an eccentric bushing (50) arranged coaxial around the cylindrical shaft (31) of the monoblock stem extension ( 10), the eccentric bushing (50) comprising an external cylindrical shaft (51 ) having a third neutral axis (51a)； and an internal cylinder (53) having a fourth neutral axis (50a) that is substantially co-linear with the second neutral axis (30a) of the monoblock stem extension (10), wherein the third neutral axis (5 l a) is parallel and offset by a distance ß from the fourth neutral axis (50a).
