THE ANKLE-JOINT. 



353 



than the lateral ligament. It is attached proximally to a marked impression on 

 the distal part of the medial malleolus, and below, in a continuous layer, to the 

 navicular, talus and cajcaneus. In it we may recognise the following special 

 bands (&) the lig. talotibiale anterius, which extends from the front of the medial 

 malleolus to the neck of the talus; (b) the lig. talotibiale posterius, stretching 

 between the back of the medial malleolus and the postero-medial rough surface 

 of the talus ; (c) the lig. tibionaviculare, which extends from the tip of the medial 

 malleolus to the medial side of the navicular body; (cT) the lig. calcaneotibiale, 

 which extends between the tip of the medial malleolus and the medial side of 

 the sustentaculum tali ; (0) lig. talotibiale profundum, which consists of deeper 

 fibres extending from the tip of the medial malleolus to the medial side of the 

 talus. 



A synovial stratum lines the fibrous stratum of the articular capsule and, as 



Medial surface of tibia 



Deltoid ligament of the ankle 



Trochlear surface of talus 



Groove for tendon of tibialis 

 posterior muscle on plantar 

 calcaneo-navicular ligament 



Groove and tunnel for the 

 tendon of flexor hallucis 

 longus muscle 

 Calcaneus 



Long plantar ligament 

 Tendon of tibialis posterior muscle (cut) 



Sustentaculum tali 

 FIG. 323. ANKLE AND TARSAL-JOINTS FROM THE TIBIAL ASPECT. 



already described, the articular cavity extends into the interval between the tibia 

 and fibula distal to the tibio-fibular interosseous ligament. Both at the front 

 and back of the ankle-joint, as well as proximally in the angle formed by the 

 three bones, the synovial membrane covers pads of fat. 



Movements at the Ankle-Joint. In the erect attitude the foot is placed at right angles to 

 the leg ; in other words, the normal position of the ankle-joint is flexion. Those movements 

 which tend to diminish the angle so formed by the dorsum of the foot and the front of the 

 leg are called dorsiflexion, while those which tend to increase the angle, i.e. to straighten the 

 foot upon the leg, are called extension. As a matter of fact neither dorsiflexion nor extension 

 is ever completely carried out, and the range of movement of which the foot is capable is limited 

 to about 90. These movements occur about an obliquely transverse axis, as is indicated by the 

 natural lateral pointing of the toes. The weight of the body falls slightly anterior to the ankle- 

 joint, so that a certain amount of muscular action is necessitated in order to maintain the foot at 

 right angles to the leg ; but additional stability is obtained from the obliquity above mentioned. 



When the foot is raised from the ground, muscular action tends naturally to produce a certain 

 amount of extension. When the foot is extended, as in standing on the toes, the posterior narrow 

 part of the talus moves forwards into the wider part of the interval between the tibia and 

 fibula, whereas in dorsiflexion, as in raising the anterior part of the foot from the ground, the 

 widest part of the talus is forced back between the tibia and fibula ; but notwithstanding the 

 difference between these two movements, the fibula remains in close contact with the talus by 

 reason of the action of the ligamentum malleoli lateralis distale and the posterior talo-fibular 

 ligament, so that lateral movement is prevented. 



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