278 



APPLIED ANATOMY. 



be injured, but the radial (musculospiral) lies on the bone in the radial (musculo- 

 spiral) groove in approximately the middle third of the bone. It comes into contact 

 with the bone posteriorly above the insertion of the deltoid and leaves the bone on 

 its outer anterior surface to pass between the brachialis anticus and brachioradialis 

 (supinator longus) muscles. Paralysis may be caused (i) by direct injury to the 

 nerve at the time the fracture is received. (2) By subsequent changes in the nerve 

 due to its being stretched over the sharp edge of a fragment. (3) By being included in 

 callus. The last is probably much more rarely the case than the two former (Fig. 291). 

 Paralysis should be examined for early in the course of treatment. Too often it 

 is detected only after the splints have been removed, and then it is apt to be ascribed 

 to improper treatment or to misapplied pressure. The symptoms of involvement of 



Deltoid 



Site of fracture 



Infraspinatus 



Teres minor 



Teres major 



Latissimus dorsi 



External head of triceps 



Flo. 290. Posterior view of a fracture of the shaft of the humerus just below the insertion of the deltoid, 

 showing the influence of that muscle in producing abduction of the upper fragment. 



the musculospiral nerve are wrist-drop and diminution of the power of supination, 

 also some sensory changes in the dorsum of the hand and forearm. 



This nerve is frequently paralyzed from pressure in cases in which there is no 

 fracture, as from sleeping on the arm, the use of crutches, and also in certain sys- 

 temic affections, such as lead poisoning. It supplies the triceps, part of the brachialis 

 anticus, brachioradialis (supinator longus), and extensor carpi radialis longior 

 muscles in the arm, and then proceeds to the forearm. The branch to the triceps is 

 given off before the nerve enters the musculospiral groove, hence is not often injured, 

 and loss of extension of the forearm is not often present; even paralysis of the other 

 muscles mentioned is not common, the forearm muscles being mostly affected. The 

 branch to the inner head of the triceps also supplies the anconeus. 



