DISLOCATIONS OF THE ELBOW. 119 



The diagnosis is very simple, for the alteration in the ana- 

 tomical relationship of bony points is very great. 



There are four prominences of bone about the elbow- joint, the 

 tip of the olecranon process, the internal epicondyle, the external 

 epicondyle and the head of the radius. Their exact relations to 

 each other and in all positions of the forearm are of the greatest im- 

 port, and a comparison of the two limbs should always be made. 



In the f ally extended position of the bones of the forearm, the 

 olecranon sinks into its proper fossa and therefore becomes less 

 prominent. Its upper margin will then be on a level with a line 

 drawn across the back of the arm from the most prominent points 

 of the epicondyles. As flexion occurs the olecranon becomes more 

 and more prominent, and sinks to a level below the intercondy- 

 lar line, and when the arm and forearm are at right angles the 

 olecranon is the lowest point of the elbow. With full flexion the 

 olecranon is carried forwards, and comes to rest anterior to the 

 lower articular extremity of the humerus. The coronoid process 

 cannot be felt, being thickly covered by the brachialis anticus 

 muscle. 



The head of the radius lies immediately below the dimple caused 

 by the line of the radio-humeral articulation, that is, a short dis- 

 tance below the external epicondyle. If the finger be placed 

 over it and the hand pronated and supinated, the radial head is 

 readily felt to rotate, while if the finger lies upon the epicondyle 

 this is found to remain stationary. 



In a backward dislocation, the normal relationship of the 

 olecranon to the other bony points is altogether lost. Further, 

 seeing that the bones of the forearm are carried backwards, the 

 length of the forearm measured from the external epicondyle to 

 the styloid process of the radius will necessarily be diminished. 



Forward displacement of the head of the radius is often 

 caused when a child is caught up by the hand. The sudden 

 strain thus thrown upon the ligaments of the wrist-joint, through 

 the metacarpus and the carpus, acts upon the head of the radius 

 rather than the ulna, and jerks the head of the radius out of the 

 orbicular ligament, with or without a laceration of the latter. 



