232 SURGICAL APPLIED ANATOMY. [Chap. xi. 



of the relation of the deltoid insertion to the seat of 

 fracture, and cannot be tabulated. The weight of the 

 arm seldom allows of more than three-quarters of an 

 inch of shortening. 



The humerus is more frequently the seat of 

 non-union after fracture than is any other bone. 

 This result is quite independent of the position 

 of the fracture in relation to the nutrient artery. 

 Hamilton's explanation is briefly this : the fracture is 

 usually so adjusted that the elbow is flexed ; this 

 joint soon becomes fixed by muscular rigidity, and 

 when any movement is made as if to flex or extend 

 the fore arm on the arm, that movement no longer 

 occurs at the elbow joint, but at the seat of fracture. 

 Thus, if the arm be in a sling, and the patient allows 

 the hand to drop by relaxing that sling, it is main- 

 tained that the bulk of that movement will take place 

 about the fracture line. Tbsre are many objections 

 to this theory. If true, the tendency to movement 

 about the fragments would be the greater the farther 

 the fracture is from the elbow joint, but non-union is 

 more common at the middle than at the upper third 

 of the shaft. Probably many causes conspire to 

 bring about non-union of fractures of this bone, 

 among which may be mentioned the imperfect fixing 

 of the joint above the fracture, and the inadequate 

 support afforded to the elbow, whereby the weight 

 of the arm and of the splints tends to drag the 

 lower fragment out of the proper line it should form 

 with the upper fragment. The most effective cause 

 would appear to be due to the entanglement of 

 muscular tissue between the broken ends, for it 

 must be remembered that the shaft of the bone is 

 closely surrounded by muscular fibres that are directly 

 adherent to its surfaces. Thus, in an oblique fracture 

 the end of one fragment may be driven into the 

 brachialis anticus, while the other end projects iuto 



