A knee joint prosthesis for implantation to replace a portion of a knee joint. The knee joint prosthesis includes a tibial tray and a bearing member that engages the tibial tray. The prosthesis also includes an insert with a base that is fixed to the bearing member and an extension portion that extends away from the bearing member and the tibial tray. The extension portion has an axis, and the extension portion includes a threaded portion. The prosthesis further includes a post that is rotatably coupled to the extension portion, and the post is rotatable about the axis of the extension portion relative to the insert. Furthermore, the prosthesis includes a retention member that threadably couples to the threaded portion of the insert to limit movement of the post along the axis away from the bearing member and the tibial tray.
