A method of assembling an orthopaedic prosthesis, the method comprising: aligning a prosthetic trial assembly (772, 1032) with a surgical instrument that includes a mounting platform and a stabilizer arm, the prosthetic trial assembly comprising a prosthetic trial component that defines a first axis (740, 1014) and an offset adaptor trial (770, 1030) that defines a second axis (788, 1060) that is offset from the first axis, positioning the prosthetic trial assembly on the mounting platform, rotating the mounting platform to position the first axis and the second axis in a plane extending vertically through the stabilizer arm, advancing the stabilizer arm along the vertically-extending plane to engage the stabilizer arm with the prosthetic trial assembly, locking the mounting platform to prevent rotation relative to the stabilizer arm, positioning a prosthetic component (16, 18) on the mounting platform after removing the prosthetic trial assembly such that a third axis (630, 930) defined by a post (616, 906) of the prosthetic component is positioned in the plane, the prosthetic component having a size and a shape that matches a size and a shape of the prosthetic trial component, positioning an offset adaptor (660, 960) on the post, the offset adaptor including an end that defines a fourth axis (686, 986) that is offset from the third axis by an amount equal to the offset of the first axis and the second axis, rotating the end of the offset adaptor to position the fourth axis in the vertically-extending plane, and securing the offset adaptor to the prosthetic component with the third axis and the fourth axis positioned in the plane. aligning a prosthetic trial assembly (772, 1032) with a surgical instrument that includes a mounting platform and a stabilizer arm, the prosthetic trial assembly comprising a prosthetic trial component that defines a first axis (740, 1014) and an offset adaptor trial (770, 1030) that defines a second axis (788, 1060) that is offset from the first axis, positioning the prosthetic trial assembly on the mounting platform, rotating the mounting platform to position the first axis and the second axis in a plane extending vertically through the stabilizer arm, advancing the stabilizer arm along the vertically-extending plane to engage the stabilizer arm with the prosthetic trial assembly, locking the mounting platform to prevent rotation relative to the stabilizer arm, positioning a prosthetic component (16, 18) on the mounting platform after removing the prosthetic trial assembly such that a third axis (630, 930) defined by a post (616, 906) of the prosthetic component is positioned in the plane, the prosthetic component having a size and a shape that matches a size and a shape of the prosthetic trial component, positioning an offset adaptor (660, 960) on the post, the offset adaptor including an end that defines a fourth axis (686, 986) that is offset from the third axis by an amount equal to the offset of the first axis and the second axis, rotating the end of the offset adaptor to position the fourth axis in the vertically-extending plane, and securing the offset adaptor to the prosthetic component with the third axis and the fourth axis positioned in the plane.