An artificial joint comprising: a first joint assembly adapted to be connected to a first bone and having a first contacting surface , wherein the first contacting surface comprises a first convex arc surface , a second convex arc surface , and a third convex arc surface ; and a second joint assembly adapted to be connected to a second bone and having a second contacting surface , wherein the second contacting surface is adapted to contact the first contacting surface and comprises a first concave arc surface , a second concave arc surface , and a third concave arc surface , and the first concave arc surface , the second concave arc surface , and the third concave arc surface respectively correspond to the first convex arc surface , the second convex arc surface , and the third convex arc surface ; wherein the second convex arc surface is adapted to be connected between the first convex arc surface and the third convex arc surface , and the second concave arc surface is connected between the first concave arc surface and the third concave arc surface ; wherein each of the first convex arc surface , the second convex arc surface and the third convex arc surface extends over a respective area and each of the first concave arc surface , the second concave arc surface and the third concave arc surface extends over a respective area; characterized in that the area of the second convex arc surface is greater than the area of the first convex arc surface and greater than the area of the third convex arc surface , and the area of the second concave arc surface is greater than the area of the first concave arc surface and greater than the area of the third concave arc surface . a first joint assembly adapted to be connected to a first bone and having a first contacting surface , wherein the first contacting surface comprises a first convex arc surface , a second convex arc surface , and a third convex arc surface ; and a second joint assembly adapted to be connected to a second bone and having a second contacting surface , wherein the second contacting surface is adapted to contact the first contacting surface and comprises a first concave arc surface , a second concave arc surface , and a third concave arc surface , and the first concave arc surface , the second concave arc surface , and the third concave arc surface respectively correspond to the first convex arc surface , the second convex arc surface , and the third convex arc surface ; wherein the second convex arc surface is adapted to be connected between the first convex arc surface and the third convex arc surface , and the second concave arc surface is connected between the first concave arc surface and the third concave arc surface ; wherein each of the first convex arc surface , the second convex arc surface and the third convex arc surface extends over a respective area and each of the first concave arc surface , the second concave arc surface and the third concave arc surface extends over a respective area; characterized in that the area of the second convex arc surface is greater than the area of the first convex arc surface and greater than the area of the third convex arc surface , and the area of the second concave arc surface is greater than the area of the first concave arc surface and greater than the area of the third concave arc surface . <EOS>