Abstract: A prosthetic ankle joint device for replacement of articular bearing surfaces of the natural joint comprises: a first component (2) for attachment to a first tibial bone segment (2a) having a first articulating bearing surface (5); a second component (3) for attachment to a second tarsal bone segment (3a) having a second articulating bearing surface (6) opposite to the first articulating bearing surface (5). The first articulating bearing surface (5) and the second articulating bearing surface (6) are substantially different in shape to the corresponding shapes of the articular bearing surfaces of the natural joint. The first surface (5) being concave, or flat, or convex. Each articulating bearing surface (5, 6) presents a respective shape designed on the basis of the shape of the opposite articulating bearing surface (5, 6) according to the common normal to their point of mutual contact at every position over the range of passive plantar and dorsi-flexion.

Abstract: A prosthesis device (1) for correct replacing of the articular surfaces of the human ankle joint comprises: a first component (2) having a spherical convex articular bearing surface (5); a second component (3) having a bearing surface (6) which has a convex shape in the frontal plane, and concave sulcus in the frontal plane; and a third component (4) located between said first and second components (2, 3) and having two surfaces (7, 8) which are complementary to and engage the upper convex and the lower concave sulcus surfaces (5, 6) to be fully congruent with the components (2, 3). The three components (2, 3, 4) can be designed from the subject-specific geometry of the ligaments (9, 10). The device (1) can move under natural muscular and ligamentous control, closely restoring that of a natural joint and maintaining uniform load distribution.