LUXATION OF THE ELBOW 8i 



hinge variety), renders lateral dislocation of the joint an impossibility 

 unless one or other of the ligaments be first ruptured. Anterior disloca- 

 tion, again, is effectually prevented by the conformation of the sigmoid 

 cavity of the ulna and the fact that the ulna is firmly ossified to the 

 back of the radius. 



Lastly, as a preventive against posterior dislocation, we have the 

 powerful tendon of insertion of the biceps and the strong anterior 

 common ligament, and in addition to these the tendon of insertion of the 

 brachialis anticus muscle crosses the front of the joint obliquely down- 

 wards and inwards in a manner which is peculiarly adapted to maintain 

 the bones in apposition. 



It is not surprising to find that luxation of this joint only occurs in 

 cases of very severe injury where the tendons or ligaments are also 

 ruptured or the bones fractured, and it will be readily gathered, from the 

 account of the extremely important large blood-vessels and nerves which 

 cross the inner aspect of the joint, that inward displacement is attended 

 with by far the most serious consequences. 



When luxation occurs diagnosis is not difficult, since the displaced 

 bones may be easily felt, and to replace them it is necessary to place the 

 animal under a general anesthetic, for by this means the muscles are 

 relaxed and the process of reduction facilitated. 



Dislocation occurs much more readily in man and the carnivora. 

 This is due to the difference in conformation of the upper extremity or 

 head of the radius. In man it is somewhat circular in outline, and its 

 upper surface is cuplike. Below this articular surface the head is 

 circumscribed by a facet which fits into the lesser sigmoid cavity of the 

 ulna. The formation of these facets is such that the head of the radius 

 may be rotated on the distal end of the humerus, and the ulna moves 

 freely round the radius through the articulation of the latter in the lesser 

 sigmoid cavity, two movements which are necessary in supination and 

 pronation, of which the dog is to a less degree capable, but which are 

 altogether impossible in the horse. There is thus much greater range of 



