A prosthesis (100, 200) comprising a bone attachment component (106) having one or more fixation structures (124, 224), wherein the prosthesis is configured to be selectively convertible between a mobile bearing prosthesis, in which a barrier (120) is secured to the bone attachment component (106) using the fixation structures, and a constrained bearing prosthesis, in which a bearing component (204) is secured to the bone attachment component (106) using the fixation structures (124, 224).