484 THE INFERIOR EXTREMITY 



synovial membrane. At this joint the inferior surface of the 

 body of the talus articulates with the upper surface of the 

 calcaneus (Fig. 144). 



The Talo-Calcaneo-Navicular Joint is formed by the head 

 of the talus,, the posterior surface of the navicular and the upper 

 surface of the sustentaculum tali. This large joint -cavity, 

 which is lined by a single synovial membrane, is closed infero- 

 medially by the plantar calcaneo-navicular ligament, and is shut 

 off from the talo-calcanean joint by the strong interosseous talo- 

 calcanean ligament. 



The -plantar calcaneo-navicular (" spring ") ligament stretches 

 from the anterior border of the sustentaculum tali to the plantar 

 surface of the navicular. It is of great strength so as to enable 

 it to support the head of the talus and the part of the body- 

 weight which it transmits. 



The Calcaneo - Cuboid Joint lies midway between the 

 lateral malleolus and the base of the fifth metatarsal. It is 

 provided with a separate synovial membrane and is supported 

 inferiorly by the short and long plantar ligaments. 



In Chopart's amputation at the " transverse tarsal " joint, 

 the talo-navicular and calcaneo-cuboid joints are cut through. 

 On the medial side, the knife is inserted behind the navicular 

 tuberosity and is carried forwards and laterally, following the 

 convexity of the head of the talus. On the lateral side the 

 knife is inserted midway between the lateral malleolus and the 

 base of the fifth metatarsal, and is carried backwards and 

 medially, following the line of the calcaneo-cuboid joint. This 

 operation does not secure a good bearing surface, as the talus, 

 which is no longer supported by the plantar calcaneo-navicular 

 ligament, is tilted forwards by the weight of the trunk and the 

 calcaneus is correspondingly tilted upwards posteriorly, despite 

 division of the tendo calcaneus. 



The joint between the medial cuneiform and the first metatarsal 

 possesses a separate joint cavity, but the remaining inter-tarsal, 

 tarso-metatarsal, and inter-metatarsal joints are frequently 

 lined by the prolongations of a single synovial membrane. 



In the amputations of Hey and Lisfranc, the foot is 

 disarticulated at the tarso-metatarsal articulation. The line 

 of the articulation passes medially and slightly forwards across 

 the foot from the lateral side. When the knife is inserted 

 behind the tuberosity of the fifth metatarsal, it must be carried 

 forwards for a short distance before the joint cavity is opened, 



