io6 Anatomy Applied to Medicine and Surgery. 



tion is so rare at this joint is, that it is surrounded by a 

 number of tendons rounded cords, which are powerful 

 agents in protecting the joint. So rare is dislocation at 

 this joint, that Dupuytren at first absolutely denied its oc- 

 currence his argument being, that it was not the ligaments 

 that prevented it, but the fact that the tendons offered 

 such resistance, that even very severe injury was insuffi- 

 cient to tear them, and that, the greater the extension at 

 the joint, the more firmly the tendons are applied to the 

 anterior surface of the wrist, thus resisting displacement. 

 In fact he estimated that it would require a force of about 

 1,000 pounds to overcome the resistance of these tendons. 



When dislocation does occur, it is generally backwards, 

 and may be diagnosed from "Colics' fracture" by the fact 

 that (1) in dislocation the projecting bones are more 

 abrupt than in the fracture; (2) that reduction may be 

 accomplished suddenly, and (3) that the relative position 

 of the styloid processes is unchanged, i.e., they bear their 

 normal relationship of the radial styloid being three- 

 eighths of an inch nearer the hand than the ulnar styloid, 

 whereas, in "Colics' fracture," the styloid process of the 

 radius is driven up to a level with, or even above, that of 

 the ulna. Dislocation of the first phalanx of the thumb, 

 backwards, is generally the result of a fall on its distal 

 end and palmar surface causing extreme dorsal flexion, 

 and is very difficult of reduction. The phalanx is gener- 

 ally at right angles to the metacarpal bone, and the ob- 

 stacle to reduction has been variously stated by different 

 writers. 



Hey considered it due to imprisonment of the head of 

 the metacarpal bone" between the two lateral ligaments. 

 Malgaigne and Erichsen stated that the head of the meta- 

 carpal was locked between the two heads of the flexor 

 brevis muscle, like a button in a button-hole. Lawrie, 



