452 



HUMAN ANATOMY. 



with it because of the greater strength of the calcaneo-scaphoid as compared with the 

 astragalo-scaphoid ligaments. As, owing to the width of the pelvis, the obliquity of 

 the femur, and the curve of the tibia, the weight of the body is transmitted to the 

 astragalus in an inward direction, it would be displaced inward {i.e., there would be 

 an outward luxation of the os calcis and scaphoid) far more frequently than in the 

 opposite direction were it not for the resistance offered by the projection of the sus- 

 tentaculum and the lesser articular process on the inner side and the outward obliquity 

 of both the processes of the posterior calcaneo-astragaloid joint. The two lateral 

 dislocations associated with some displacement backward are, therefore, about equal 

 in frequency. The extensive opposed articular surfaces of the os calcis and astragalus 

 are not, as a rule, completely separated ; the smaller surfaces of the astragalo-scaphoid 

 joint are, so that the one is a subluxation, the other a complete luxation. 



The ligaments uniformly torn are the interosseous calcaneo-astragaloid, the 

 astragalo-scaphoid, and one or other of the lateral ligaments of the ankle. 



In inward and backward luxation the symptoms are (a) shortening of the line 

 between the mid-point of the ankle and the web of the great toe ; {b) projection and 

 lengthening of the heel ; (r) inversion and adduction of the foot, the inner border 

 shortened and concave, the outer lengthened and convex ; {d) partial disappearance 

 of the internal malleolus ; (^) projection of the sustentaculum tali beneath and behind 

 it ; (/) projection of the external malleolus and of the head of the astragalus on the 

 outer side of the dorsum, with yielding spaces in the soft parts beneath each. The 

 axis of the leg, when continued downward, falls to the outer side of, or even external 

 to, the foot. The scaphoid can be felt on the inner side of the foot. The deformity 

 resembles that of talipes varus. 



In outward and backward luxation a and b are the same ; there are abduction and 

 eversion of the foot, and disappearance of the outer and prominence of the inner 

 malleolus ; the deformity resembles that of talipes valgus. 



The medio-tarsal — astragalo-scaphoid and calcaneo-cuboid — articulation usually 

 escapes injury on account of the elasticity of the anterior pillar of the arch of the foot 

 (into which it enters) and because of the numerous joints of the anterior tarsal and 

 the metatarso-phalangeal regions which take up and diffuse force applied to the 

 anterior part of the foot. 



The first metatarsal bone is more frequently dislocated from the tarsus than any 

 of the others, as, relatively to the other phalanges, are the proximal phalanx and the 



Fig. 467. 



First metata 



Fourth metatarsal 



Sesamoi d bones 

 Section of right foot through heads of metatarsal bones, showing support by first and fourth. 



terminal phalanx of the same toe. These dislocations are nearly always upward. 

 Dislocation of the proximal phalanx of the great toe may be as difficult to reduce 

 as is that of the thumb. Morris thinks that the sesamoid bones may act as the 

 anterior ligament does in the latter case, — i.e.., being more firmly attached to the 

 phalanx than to the metatarsal bone, they may be torn away with the former, and by 

 their interposition prevent reduction. 



The painful affection known as tnetatarsalgia has been thought (Morton) to be 

 due to the position of the fifth metatarso-phalangeal joint, so much posterior to the 

 fourth that the base of the first phalanx of the little toe is opposite the head and neck 

 of the fourth metatarsal. As the fourth and fifth metatarsal bones have greater 

 mobility than their fellows, it was supposed that this relation afforcied opportunity for 



