THE ARM. 



277 



There are two main points where fracture occurs; immediately above the inser- 

 tion of the deltoid and below it. 



Fractitre above the Insertion of the Deltoid. The bone may be fractured imme- 

 diately above the deltoid insertion. In this case the powerful axillary fold muscles, 

 pectoralis major, teres major, and latissimus dorsi, being attached to the upper frag- 

 ment, tend to draw it toward the body, while the deltoid tends to draw the lower 

 fragment out. The influence of the other muscles, biceps, coracobrachialis, and triceps, 

 would be to increase the overlapping (Fig. 289). 



Fracture below the Deltoid Insertion. This is the more common site of fracture. 

 The line of fracture is most apt to be from above downward and outward. The 

 upper fragment is displaced anteriorly by the coracobrachialis and anterior portion 



Pectoralis major 



Latissimus dorsi 



Deltoid 



Teres major 



FIG. 289. Fracture of the shaft of the humerus just above the insertion of the deltoid and below the inser- 

 tion of the axillary fold muscles. The lower fragment is seen to be drawn outward by the deltoid; the upper frag- 

 ment is seen to be drawn inward by the pectoralis major, latissimus dorsi, and teres major. 



of the deltoid and is drawn outward by the deltoid aided by the supraspinatus. To 

 relax the deltoid the arm is sometimes dressed in an abducted position (Fig. 290). 



Non-Union. The humerus has muscles attached to it almost throughout its 

 entire length, and when the sharp ends of the fragments are displaced they probably 

 become fixed in the surrounding muscle, and proper apposition of the fragments is 

 prevented, hence non-union. Hamilton believed that lack of proper fixation was also 

 a prominent cause. 



The Radial (Musculospiral) Nerve. In fracture of the shaft of the 

 humerus, paralysis of the extensors due to injury of the radial nerve is compara- 

 tively common. It also occurs from pressure due to the use of crutches, to sleep- 

 ing on the arm, etc. The other nerves are too far removed from the bone to 



