chap, xiii.] REGION OF ELBOW. 221 



when in the antero-posterior direction, and partial 

 when the luxation is lateral. 



Some more detailed notice may now be taken 

 of the only two forms of dislocation at the elbow that 

 are at all common. 



(1) Displacement of* both bones back- 

 ward s. This may be effected during forced exten- 

 sion. Here the point of the olecranon pressed against 

 the humerus acts as the fulcrum of a lever of the 

 second kind, and tends to tear the ulna from the 

 latter bone. The addition of violence to the fore-arm 

 in a backward or upward direction would effect the 

 actual displacement. This condition may be illustrated 

 by a fall, as in running, upon the fully extended 

 hand. The lesion may also be produced by certain 

 violent wrenchings of the limb. Malgaigne maintained 

 that the particular kind of wrench most effectual in 

 producing luxation was a twisting inwards of the 

 fore-arm while the elbow was semi-flexed. In this 

 way the internal lateral ligament was ruptured, and 

 the coronoid process twisted inwards and downwards 

 under the humerus, and the bones thus displaced back. 

 This lesion would be difficult to effect while the joint 

 was fully flexed. In the complete form the coronoid 

 process is opposite to the olecranon fossa. It can 

 hardly occupy that hollow (as sometimes described), 

 since the connection of the ulna to the radius, and the 

 projection of the latter bone behind the outer condyle, 

 would prevent it from actually falling into the fossa. 

 The anterior and the two lateral ligaments are usually 

 more or less entirely torn, while the posterior and the 

 orbicular ligaments escape. The biceps is drawn over 

 the lower end of the humerus, and is rendered 

 moderately tense. The brachialis anticus is much 

 stretched and often torn. The anconeus is made very 

 tense. Both the median and ulnar nerves may be 

 severely stretched. 



