A prosthesis assembly (100) for orthopaedic implantation comprises a prosthesis body (110) and an attachment portion (112) coupled to the prosthesis body (110) for attaching the prosthesis assembly (100) to a bone by way of a bone anchor (120) or other fixating means. The attachment portion (112) comprises an opening (130) having a receiving portion (132) with a first crosssectional transverse width and a retaining portion (134) extending from the receiving portion (132), the retaining portion (134) having a second cross-sectional transverse width, which is less than the first cross-sectional transverse width. A system comprising the prosthesis assembly (100) includes a bone anchor (120) having a fastening member (124) for engaging the opening (130) and a stem (122) for securing to the bone.
