236 APPLIED ANATOMY. 



arm to the side the distance from the acromion process to the external condyle is 

 increased, with the arm abducted to a right-angle, the same distance is decreased as 

 compared with the previous position as well as when compared with the arm of the 

 opposite side (see Fig. 248). 



1. Lowering the shoulder obviates pain by relaxing the deltoid and preventing 

 it from forcing the head upward in its displaced position. 



2. Flattening of the shoulder is due to the head and tuberosities being displaced 

 inward, thus leaving the socket empty. A marked depression can be felt with the 

 fingers below the prominent acromion process. 



3. Projection of the elbow from the side is due to tension of the deltoid muscle 

 because the head is lower than normal. In its natural position the top of the head is 

 about level with the coracoid process; when luxated it is below it. 



4. The normal hollow below the outer third of the clavicle is lost because here is 

 where the head lies. It may form a distinct prominence and when the arm is rotated 



FIG. 248. Subcoracoid dislocation of the shoulder. The head of the humerus has slipped off its pedestal or 

 shoulder-girdle onto the side of the thorax. This shows how the arm is shortened and why it is necessary to 

 make traction in order to replace the humerus up again on the shoulder-girdle. 



if the surgeon lays his hand at this point the tuberosities can be felt to rotate beneath. 

 If the arm is abducted the head can usually be felt in the axilla, where it may even 

 form a prominence. 



5. In Dugas's test the elbow cannot be brought to the chest because the outer 

 end of the humerus is held close to the chest-wall. On account of the thorax being 

 rounded like a barrel it is necessary for the outer end of the bone to rise as the inner 

 end falls. 



6. The reason for the difference in measurements when the shoulder is luxated 

 is readily seen by the fact that the head is displaced downward and inward as shown 

 in the accompanying figure. 



TREATMENT. 



Reduction of an anterior luxation of the shoulder can be accomplished in two 

 ways, viz. , the direct, in which the head is pulled or pushed back into the socket, 

 and the indirect, in which it is levered back. 



Direct Method. This consists in first placing the arm in approximately the 

 position it occupied when luxated (abduction) and then pulling or pushing the 

 head toward and into the socket while the arm is rotated to relax the capsule and 

 allow the head to enter. The usual obstacle to reduction of a recent luxation is 

 muscular contraction. The main muscles acting are the deltoid, pectoralis major, 

 latissimus dorsi, and teres major. To effect reduction the action of these muscles 

 must either be held in abeyance or overcome by force. This may be accomplished 

 in several ways, viz. , by the use of general anaesthesia, by such gentle manipulations 



