526 SURGICAL A /'PLIED ANATOMY. [Chap. xxm. 



Subastragaloid dislocations of the foot. 



In these lesions, which are not very uncommon, the 

 astragalus remains in position between the tibia and 

 fibula, while the rest of the foot is dislocated below 

 that bone. The luxation, therefore, concerns the 

 calcaneo-astragaloid and astragalo -scaphoid joints. 

 The foot may be displaced either forwards, backwards, 

 or laterally. The forward dislocation is extremely 

 rare, and the lateral luxations are nearly always 

 oblique. In the most usual displacement the foot is 

 dislocated outwards or inwards, and is at the same 

 time carried backwards. These luxations are often 

 compound, especially when lateral. They are, as a rule, 

 incomplete as regards the calcaneo-astragaloid joint, 

 while, on the other hand, the displacement of the astra- 

 galus from the scaphoid is in nearly every instance com- 

 plete. In all cases the interosseous ligament between 

 the os calcis and astragalus must be torn, and there will 

 also be more or less laceration of the astragalo-scaphoid 

 ligament, and of one or both of the lateral bands of the 

 ankle joint. The malleoli are very often fractured. 



It is only necessary to notice in any detail the two 

 lateral luxations, as being the only common forms. In 

 the inward dislocation the foot is inverted, its inner 

 border is raised, is shortened, and rendered concave, 

 while its outer border is lengthened and made convex. 

 The deformity much resembles that of talipes varus. 

 The head of the astragalus with the outer malleolus 

 form a projection at the outer aspect of the foot, while 

 below them a deep hollow exists. The inner border of the 

 os calcis is very prominent at the internal side of the 

 limb, while the inner malleolus is buried in the hollow 

 left by the displacement of that bone. The calcaneum 

 and scaphoid are approximated. In the outward 

 luxation the foot is abducted, its outer border is raised, 

 and the deformity produced is not unlike that of talipes 

 valgus. The outer malleolus is lost in the hollow 



