PRACTICAL CONSIDERATIONS : THE FOREARM. 



605 



Fig. 



Pronator 

 radii teres 



Pronator 

 quadratiis 



Fig. 5S5. 



Biceps 



Brachio- 

 radialis 



Upper 

 fragment 



Lower 

 fragment 



Tendon ot 



triceps 



Internal 

 condyle 



Separated 

 olecranon 



Ulna 

 Radius 



and the mid-position between pronation and supination sufficiently relax the biceps 

 and the pronator radii teres. The weight of the hand in adduction overcomes the 

 pull of the brachio-radialis 

 and pronator quadratus. 



Fracture of both bones, 

 from either direct or indirect 

 violence, usually takes place 

 below the middle of the fore- 

 arm, as there the muscular 

 masses which protect the 

 upper half of the radius from 

 direct violence have largely 

 been replaced by tendons, 

 the ulna is slender and weak, 

 and the opposing forces rep- 

 resented by the biceps and 

 brachialis anticus above and 

 the weight or force applied 

 through the hand expend 

 themselves. Thus Malgaigne 

 (quoted by Agnew) reports 

 a case in which both bones 

 were broken by muscular 

 action alone while the patient 

 was carrying weight in the 

 .form of a shovelful of dirt. 

 When the resulting deform- 

 ity is due chiefly to the con- 

 traction of muscles, it is apt 

 to consist in flexion of both 

 upper fragments by the bi- 

 ceps and brachialis anticus, 

 supination of the upper frag- • 

 ment of the radius by the 

 biceps and supinator brevis, 

 and approximation of the two 

 lower fragments by the pronator quadratus. Much overlapping and shortening are 

 usually prevented by the untorn fibres of the interosseous membrane. 



During the period of repair the mid-position — between pronation and supination 

 — preserves the parallelism of the two bones, maintains the interosseous space at 



almost its greatest 

 Fig. 586. width, relaxes (in 



conjunction with 

 the flexion of the 

 elbow) the muscles 

 involved so far as 

 is possible, and by 

 the weight of the 

 hand dropping to 

 the ulnar side over- 

 comes the resist' 

 ance of others, espe- 

 cially of the brachio- 

 radialis. 



The large pro- 

 portion of the re- 

 turn current of 



blood that is carried by the superficial veins of the forearm makes it especially impor- 

 tant that the splints used should be so broad that the bandage does not unduly com- 



***, ,, 



Dissection of fracture of radius between 

 the two pronator muscles. 



Dissection of fracture of ole- 

 cranon process of left ulna ; joint 

 opened from behind. 



Ext. carpi radialis long. 

 Ext. carpi radialis brev. 



Lower fragment 

 Brachio-radialis 

 Ext. longus pollicis 



Radial artery 

 Flexor tendons 

 Lower end of upper fragment 

 Ext. brevis and ext. ossis met. poll., 

 cut and turned forward 



Dissection of Colles's fracture of radius, showing relation of tendons and radial 



artery. 



