Abstract: In a prosthetic ankle joint, a first component has a lower articular bearing surface and is configured for connection to the distal end of the tibia such that the lower articular bearing surface is remote from the tibia. A second component has an upper articular bearing surface and is configured for connection to the tarsal bone such that the upper articular bearing surface is remote from the tarsal bone. A third component is interposed between the first and second component and has an upper bearing surface configured to be slidable on the lower bearing surface of the first component and a lower bearing surface configured to be slidable on the upper surface of the second component. At at least one of the components and/or bearing surfaces is configured to allow the third component to be slidable in an anterior/posterior direction but to prevent the third component being slidable in a medial/lateral direction.