An assembly comprising: a medical implant comprising: a cup prosthesis having a circumference and a central axis which defines an axial direction and a radial direction; and an attachment member applied around the circumference of the cup, wherein the attachment member comprises: a circumferential band; and at least two tabs extending in the axial direction from the circumferential band and having a circumferential region of weakness, each of the at least two tabs delimiting an opening; and an instrument head (2, 24, 102, 202) attached to the attachment member and engaged with the cup prosthesis, the instrument head comprising an axial retaining element extending from the instrument head and engaged with the opening of the at least two tabs, characterised in that the axial retaining element (12, 112, 212) extends from the instrument head in the radial direction and each of the at least two tabs delimit an opening in the radial direction adapted for engagement by the radially extending axial retaining element. a medical implant comprising: a cup prosthesis having a circumference and a central axis which defines an axial direction and a radial direction; and an attachment member applied around the circumference of the cup, wherein the attachment member comprises: a circumferential band; and at least two tabs extending in the axial direction from the circumferential band and having a circumferential region of weakness, each of the at least two tabs delimiting an opening; and an instrument head (2, 24, 102, 202) attached to the attachment member and engaged with the cup prosthesis, the instrument head comprising an axial retaining element extending from the instrument head and engaged with the opening of the at least two tabs, characterised in that the axial retaining element (12, 112, 212) extends from the instrument head in the radial direction and each of the at least two tabs delimit an opening in the radial direction adapted for engagement by the radially extending axial retaining element. a cup prosthesis having a circumference and a central axis which defines an axial direction and a radial direction; and an attachment member applied around the circumference of the cup, wherein the attachment member comprises: a circumferential band; and at least two tabs extending in the axial direction from the circumferential band and having a circumferential region of weakness, each of the at least two tabs delimiting an opening; and a circumferential band; and at least two tabs extending in the axial direction from the circumferential band and having a circumferential region of weakness, each of the at least two tabs delimiting an opening; and an instrument head (2, 24, 102, 202) attached to the attachment member and engaged with the cup prosthesis, the instrument head comprising an axial retaining element extending from the instrument head and engaged with the opening of the at least two tabs, characterised in that the axial retaining element (12, 112, 212) extends from the instrument head in the radial direction and each of the at least two tabs delimit an opening in the radial direction adapted for engagement by the radially extending axial retaining element.