THE FOREARM. 



323 



These fractures are of interest from an anatomical point mainly on account of 

 the influence of rotation and muscular action in displacing the fragments. The fore- 

 arm possesses the movement of rotation; the radius is the movable bone and rotates 

 around the ulna, hence when it is broken 

 its fractured ends are readily displaced. 

 Fractures of this bone are to be treated 

 with the hand in half or full stipulation 

 because in these positions the interosse- 

 ous space is preserved. In pronation 

 the radius crosses the ulna obliquely and 

 lies close upon it and is then most liable 

 to be bound to it by callus. A cer- 

 tain amount of callus or deformity may 

 occur without interfering with the ulna 

 opposite. 



It should also not be forgotten that 

 most muscles have more than one ac- 

 tion. The biceps is both a flexor and 

 supinator. The brachioradialis flexes, 

 supinates, and exerts a directly upward 

 traction on the outer surface of the lower 

 end of the radius. 



The fractures of the shaft of the 

 radius may be divided into those above 

 and those below the insertion of the pro- 

 nator radii teres. This muscle inserts 

 by a comparatively small tendon into 

 the outer and posterior surface of the 

 middle of the radius. 



Fractures above the Insertion of the 

 Pronator Radii Teres. When the bone 

 is fractured above the pronator radii 



-Biceps 



Supinator (brevis) 



_Brachioradialis (supi- 

 nator longus) 



"Pronator radii teres 



-Upper fragment 



Lower fragment 



Deep flexor muscles 



Pronator quadratus 



teres insertion, and below the tubercle, 

 the upper fragment is drawn forward 

 and rotated outward by the biceps. If 

 the fracture is down close to the upper 

 edge of the insertion of the pronator 

 radii teres the supinator (brevis) will 

 assist in the supination. The lower frag- 

 ment will be pronated by the pronator 

 radii teres and quadratus. It will be 

 drawn toward the ulna by the teres, 

 quadratus, and also by the action of the 

 brachioradialis. The pronator radii teres 

 will also tend to draw the lower frag- 

 ment anteriorly. The injury is to be 

 treated with the elbow flexed to relax 

 the biceps and in a fully supinated posi- 

 tion (Fig. 332). 



Fractures below the Insertion of the 

 Pronator Radii Teres. When the frac- 

 ture is below the insertion of the pro- 

 nator radii teres and above the pronator 

 quadratus we have the lower fragment 

 drawn toward the ulna by the pronator quadratus and the brachioradialis. The 

 quadratus also tends to pronate the hand (Fig. 333). 



The upper fragment is displaced anteriorly by the flexing action of both the biceps 

 and pronator radii teres. The supinator (brevis) and biceps both tend to supinate 

 it and the pronator radii teres to pronate it. This tends to place the upper fragment 



FIG. 332. Fracture of the shaft of the radius above 

 the insertion of the pronator radii teres muscle. The 

 upper fragment is rotated outward by the biceps and 

 supinator muscles. 



