120 CLINICAL APPLIED ANATOMY. 



The immediate consequence of this displacement is a pro- 

 nounced alteration in the relationship of the head of the radius 

 to the external condyle of the humerus when compared with the 

 opposite, normal, side. The prominence of the head of the bone 

 in front of the capitellum explains the reason why flexion is so 

 limited, seeing that the head soon comes in contact with the soft 

 tissues of the arm. 



The bone can usually be comparatively easily reduced into 

 position, but the difficulty is to maintain it there. This difficulty 

 is entirely due to anatomical reasons. If the orbicular ligament 

 is lacerated, there is nothing to keep the head of the radius in 

 place, while if this ligament remains intact, it is impossible by 

 manipulation to reinsert the head of the radius within it. 



Dislocations at the Wrist Joint. These dislocations are of 

 extreme rarity, probably owing to the strength of the ligaments of 

 the radio-carpal articulation and the manner in which the strain 

 of a fall upon the palm of the hand is shared by the several articu- 

 lations of the carpus. When, however, one does occur it is usually 

 backward. In these dislocations it will be noticed that the 

 styloid processes retain their normal anatomical relationship, 

 namely, that of the radius being at a somewhat lower level than 

 that of the ulna, and further that the hand has little or no 

 tendency to a radial displacement. Both of these facts serve to 

 distinguish this dislocation from fracture of the lower end of the 

 radius or separation of its distal epiphysis. 



Dislocations at the Metacarpo-phalangeal Joints. These are 

 most frequently seen in the case of that of the thumb, in which 

 the proximal phalanx is displaced backwards. 



The anterior ligament is stretched and the head of the meta- 

 carpal bone tears it transversely away from its attachment, and 

 when the base of the phalanx is displaced backwards the sheet 

 of glenoid ligament is carried with it so as to come to lie on the 

 dorsal aspect of the metacarpal bone. Sometimes, however, the 

 anterior or glenoid ligament is split vertically, when one half 

 will lie embracing either side of the neck of the metacarpal bone 

 when the phalanx is dislocated dorsally. In all the backward 



