This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The ankle-joint is a pure hinge-joint and its motion is anteroposterior except in complete extension, when a small amount of lateral movement is possible. The range of movement is 80 degrees; 20 degrees flexion, and 60 degrees extension.
The tibia and fibula above articulate with the surface of the body of the astragalus below. The articular facet for the fibula is about twice as long from above downward as is that for the internal malleolus. The hollow below the internal malleolus is filled by the internal lateral ligament and the tendon of the tibialis posterior. The inferior tibiofibular joint is sometimes practically lacking, there being almost no continuation of the ankle-joint up between the tibia and fibula. The junction of these two bones is very strong, the ligaments being an anterior, posterior, interosseous, and a transverse inferior tibiofibular ligament which passes across the back of the ankle-joint reinforcing the posterior portion of the capsular ligament. The upper surface of the astragalus is one-fourth wider in front than behind, so that in extension it is not so firmly locked between the malleoli as in flexion (Fig. 568). Its upper surface is slightly concave. Flexion and extension take place on a transverse axis passing through the body of the astragalus at the tip of the external malleolus. This axis is not exactly transverse but is slightly oblique, so that on extension the foot is pointed slightly outward. The ankle has a capsular ligament which is very thin in front and behind the joint. Posteriorly it is reinforced above by the transverse inferior tibiofibular ligament. The flexor longus hallucis also supports it posteriorly. The internal and external lateral ligaments are strong, the internal being the stronger. The internal lateral or ligamentum deltoideum runs from the malleolus above to the scaphoid, astragalus, and calcaneum below. It is crossed on its surface by the tendons of the tibialis posterior and flexor longus digitorum muscles (Fig. 569).
The external lateral ligament has three fasciculi: an anterior one to the astragalus; a middle one to the side of the calcaneum, and a posterior one to the posterior part of the astragalus (Fig. 570). In both extreme flexion and extension the edges of the tibia come in contact with the astragalus and hence limit further movement. The ligaments also aid in restricting motion.
Fig. 568. - The upper articular surface of the astragalus, showing it to be slightly concave and one fourth wider in front than behind.
Fluid tends to find exit from the joint first anteriorly under the extensor tendons, next it tends to exude posteriorly and makes its appearance as a swelling on each side of the tendo calcaneus (Achillis). The ankle-joint is a comparatively tight one and in acute inflammations holds but little effusion. When injected it assumes the position of a right angle and flexion does not occur as
Fig. 569. - View of inner side of ankle-joint, showing the internal lateral ligament in other joints (Fig. 571). The rounded appearance of the ankle in tuberculous and other affections is not due so much to effusion within the joint as to inflammatory and tuberculous exudate in the tissues around the joint.