The ankle joint consists of 3 bone, 7 ligaments and 7 muscle/tendon units. It is not a simple hinge joint, but a rather complex joint with rolling and sliding motion in 3 planes! It is robust and long lasting - if it remains stable and the bones fit together like the pieces of a puzzle. However, if it becomes unstable, or if the bones do not fit perfectly, it soon starts to wear out, causing permanent damage to the smooth cartilage lining, with worsening pain, swelling, stiffness and deformity. This pathological process is called post traumatic arthritis.