An orthopaedic knee prosthesis assembly, comprising: a first prosthetic component configured to be implanted into a bone of a patient, the prosthetic component including (i) a surface configured to contact the bone and (ii) a stem post extending away from the surface along an axis, the stem post having a tapered bore, a first passageway, and a threaded second passageway connecting the tapered bore and the first passageway, a second prosthetic component including a tapered post received in the tapered bore of the first prosthetic component, the tapered post having (i) a bore formed therein extending along the axis and (ii) a threaded aperture defined at an end of the bore, and a fastener comprising (i) a head received in the first passageway and (ii) an elongated shaft extending through the threaded second passageway along the axis, the elongated body having a proximal end configured to be positioned in the threaded aperture, a threaded section at the proximal end, and an unthreaded section between the head and the threaded section, and a retention device for preventing the proximal end of the fastener from reentering the threaded second passageway after advancing the end of the fastener through the threaded second passageway, characterised in that the retention device has a cylindrical body with a bore extending through it, in which the bore has a diameter which is greater than the diameter of the unthreaded section of the elongated shaft but which is smaller than the diameter of the threaded section of the elongated shaft, such that the unthreaded section of the elongated shaft, but not the threaded section of the elongated shaft, can slide within the bore, the cylindrical body of the retention device being made from a polymeric material and configured to be retained in the first passageway or in the threaded second passageway. a first prosthetic component configured to be implanted into a bone of a patient, the prosthetic component including (i) a surface configured to contact the bone and (ii) a stem post extending away from the surface along an axis, the stem post having a tapered bore, a first passageway, and a threaded second passageway connecting the tapered bore and the first passageway, a second prosthetic component including a tapered post received in the tapered bore of the first prosthetic component, the tapered post having (i) a bore formed therein extending along the axis and (ii) a threaded aperture defined at an end of the bore, and a fastener comprising (i) a head received in the first passageway and (ii) an elongated shaft extending through the threaded second passageway along the axis, the elongated body having a proximal end configured to be positioned in the threaded aperture, a threaded section at the proximal end, and an unthreaded section between the head and the threaded section, and a retention device for preventing the proximal end of the fastener from reentering the threaded second passageway after advancing the end of the fastener through the threaded second passageway, characterised in that the retention device has a cylindrical body with a bore extending through it, in which the bore has a diameter which is greater than the diameter of the unthreaded section of the elongated shaft but which is smaller than the diameter of the threaded section of the elongated shaft, such that the unthreaded section of the elongated shaft, but not the threaded section of the elongated shaft, can slide within the bore, the cylindrical body of the retention device being made from a polymeric material and configured to be retained in the first passageway or in the threaded second passageway.