THE TIBIO-FIBULAR UNION 



265 



(c) The Inferior Tibio-fibular Articulation 

 Class. — Diarthrosi.s. Subdivision. — Arthrodia. 



This junction is formed l)y the lower ends of the tibia and fibula. The rough 

 triangular surface on each of these bones formed by the bifurcation of their inter- 

 osseous lines is closely and firmly united by the inferior interosseous ligament. 

 The fibula is in actual contact with the tibia by an articular facet, which is small 

 in size, crescentic in shape, and continuous with the articular facet of the malleolus. 



The ligaments which unite the bones are: — 



1. Anterior inferior tibio-fibular ligament. 



2. Posterior inferior tibio-fibular ligament. 



3. Transverse ligament. 



4. Inferior interosseous ligament. 



The antero-inferior tibio-fibular ligament (figs. 252 A and 2o.5) is a strong 

 triangular band about three-quarters of an inch (2 cm. ) wide, and is attached to the 

 lower extremity of the til)ia at its anterior and external angle, close to the margin 

 of the facet for the astragalus, and passes downwards and outwards to the anterior 



Fig. 252 A. — Lower Ends of Left Tibia and Fibula, showing the Ligaments. The 

 synovial fold between these bones has been removed to show the transverse ligament forming 

 part of the capsule of the joint, and the deeper fibres of the anterior inferior tibio-fibular liga- 

 ment which come into contact with the astragalus. 



(From a dis-section by Mr. W. Pearson, of the Eoval College of Surgeons' Museum.) 



I Anterior inferior tibio- 

 j fibula ligament 



External lateral ligament 



Internal lateral 

 ligament 



Transverse ligament 



Posterior inferior tibio- 

 fibular ligament 



border and contiguous surface of the lower end of the fibula, some fibres passing 

 along the edge nearly as far as the origin of the anterior fasciculus of the external 

 lateral ligament. The fibres increase in length from aljove downwards. In front 

 it is in relation with the peroneus tertius and deep fascia of the leg, and gives origin 

 to fibres of the anterior ligament Of the ankle-joint. Behind, it lies in contact with 

 the interosseous ligament, and comes into contact with the articular surface of the 

 astragalus (see figs. 252 A and 252 B). 



The postero-inferior tibio-fibular ligament (figs. 254 and 255) is very similar 

 to the anterior, extending from the ])osterior and external angle of the lower end of 

 the tibia downwards and outwards to the lowest half-inch ( 1 '5 cm. ) of the border 

 separating the internal from the posterior surface of the shaft of the fibula, and to 

 the upi)er part of the posterior Ijorder of the external malleolus. It is in relation 

 in front with the interosseous ligament; l^elow, it touches the transverse ligament. 



The inferior interosseous ligament is a dense mass of short felt-like fibres, 

 passing transversely l»etween and liniily uniting the oi)posed rough triangular 

 surfaces at the lower ends of the tiV)ia and fibula, except for three-eighths of an 

 inch (1 cm.) at the extremity, where there is a synovial cavity. It extends from 

 the anterior to the posterior tibio-fibular ligaments, reaching upwards an inch and 

 a half in front (4 cm.). l)Ut only half this height behind. 



The transverse ligament (fig. 254) is a strong rounded band, attached to nearly 

 the whole length of the inferi(.)r border of the posterior surface of the tibia, just above 



