60 Anatomy Applied to Medicine and Surgery. 



the humerus there is a possibility of the ends of the frag- 

 ments injuring the circumflex nerve, if the break be situ- 

 ated at the upper third, or. the musculo spiral nerve, if the 

 break be near the middle third of the bone. Should sym- 

 ptoms of irritation of these netves symptoms such as pain, 

 numbness or spasm of the muscles supplied by them ap- 

 pear shortly after the accident, they are probably due to 

 direct injury from the ends of the fragments. If, how- 

 ever, the symptoms of nerve disturbance come on some 

 time after the accident, they are in all probability due to 

 compression of the nerves by the callus that is formed. Non- 

 union occurs more frequently in this bone than in any 

 other, and various reasons have been assigned therefor, 

 such, for instance, as separation of the ends of the fragments, 

 interposition of muscular tissue, or over-extension of the 

 lower fragment, etc. Hamilton in his " Fractures and Dis- 

 locations " considers that the non-union is due to the fact 

 that, when this fracture is put up with the forearm at a right 

 angle, as it usually is, the muscles soon become rigid, pro- 

 ducing a certain amount of ankylosis. Any movement there- 

 after of the forearm causes motion at the break rather than 

 at the joint, and such movement is of a to and fro nature. 

 At first glance one would consider that movement would 

 not interfere with union since the clavicle unites in spite 

 of movement, or rather, one might seem justified in think- 

 ing that movement assists union, as evidenced by the am- 

 bulatory treatment of fractures of the leg, but, in fracture 

 of the clavicle, or, in the ambulatory treatment of fractures 

 of the leg, union is dependent on motion of a somewhat 

 rotatory character, i.e., along the axis of the bone. Where- 

 as in movement of the ankylosed arm, the motion is 

 of a to and fro character, and such movement would 

 tend to break down rather than to increase the callus 

 lormation. 



