76 THE SURGICAL ANATOMY OF THE HORSE 



" tucking up " of the limb would bring about the simultaneous flexion 

 of both these joints in the manner required. 



From the disposition of the tendons of the subscapularis and infra- 

 spinatus muscles respectively, on the inner and outer aspects of the joint 

 in the normal condition, abduction and adduction are to a great degree 

 restricted, since one tendon acts in this respect in antagonism to the other. 

 When the humeral head is displaced, however, this antagonism is removed 

 and abduction and adduction are much more easily effected. It is naturally 

 deduced, however, that there will be greater difficulty in flexing the joint, 

 and still greater in bringing about extension. In addition to these 

 symptoms careful palpation will reveal a marked difference in the position 

 of the summit of the external humeral tuberosity relative to that of the 

 coracoid process, a difference which is not difficult to detect, particularly if 

 the case is seen early and before much swelling of the parts has occurred. 



To reduce the luxation it becomes necessary forcibly to extend the 

 shoulder. Owing to the extreme care with which it is necessary to cast 

 the patient, some operators prefer to attempt reduction with the animal 

 in the standing position. A cord is applied to the limb below the knee 

 and by two or three assistants drawn forwards. Another assistant applies 

 pressure to the front of the knee to prevent flexion of this joint, and the 

 operator meanwhile endeavours to force the upper end of the humerus 

 back into position by pressing the front of the shoulder. If the operation 

 is successful the bone slips back into position with a snap, and that it is in 

 position is evident by the fact that the shoulder joint may now be flexed 

 and extended. 



WRENCHED SHOULDER 



Wrenching of the shoulder is not common on account of the 

 absence of firm ligamentous union. The capsular ligament, together 

 with the tendons which take the place of lateral ligaments, per- 

 mit of a much greater range of movement between the articular surface. 



