PRACTICAL CONSIDERATIONS : THE RADIUS. 



295 



Fig. 309. 



A 



and hand not only thus impales the lower fragment on the upper, but necessarily 

 carries the former to a higher level. In addition, the ulno-carpal fasciculus of the 

 common ligament drags on the lower end of the ulna, and either causes fracture of 

 the styloid process, into the side and base of which it is attached, or causes the lower 

 end of the ulna to project unduly on the antero-internal aspect of the wrist. The 

 stripping up of the periosteum, the laceration of the tendon sheaths that are so closely 

 applied to the bone, — especially the flexor tendons by the jagged edge of the upper 

 fragment, — and the consequent effusion are the chief 

 remaining anatomical factors in producing the character- 

 istic deformity of this most common of all fractures. The 

 lower fragment is found on the dorsum of the wrisV 

 The lower end of the upper fragment is found anteriorly 

 beneath the pronator quadratus or under the flexor ten- 

 dons (Fig. 586). The styloid process of the radius is on 

 a higher level than that of the ulna ; in dislocation of the 

 wrist this is not the case. The hand is carried towards 

 the radial side (Fig. 309). 



In cases with but very trifling displacement it is 

 still possible to recognize the absence of the projection 

 of the anterior articular lip of the bone on the front of 

 the wrist, and some slight elevation of the dorsum. 

 The angle between the axis of the forearm and the 

 ground is said (Chiene) to determine whether in such 

 a fall the line of force passes upward in front of the axis 

 of the forearm and the radius is broken, or extends up 

 the forearm itself, resulting in a sprain of the wrist or a 

 dislocation of the bones of the forearm backward at the 

 elbow. The forward sloping of the carpal surface of the 

 radius causes the posterior edge of the bone to receive 

 the greater part of the force ; hence the lower fragment 

 is rotated backward on a transverse axis, and hence the 

 disappearance of the prominence of the anterior articular 

 lip. The carpal surface of the radius also slopes down- 

 ward and outward ; hence the radial edge of the lower 

 fragment receives (through the ball of the thumb) a 

 greater part of the shock than the ulnar edge, which is, 

 moreover, firmly attached by the triangular ligament. 

 This favors the upward displacement of the radial styloid 

 and the radial displacement of the hand. There are 

 almost always some crushing and distortion of the lower 

 spongy fragment, even when it is not materially displaced. 



Anterior displacement of this fragment may occur 

 when the force is applied in the reverse direction, — i.e., 

 with the hand in forced palmar flexion. The infre- 

 quency of falls on the back of the hand explains the 

 rarity of this accident, but the greater weakness of the 

 posterior ligament and the absence of any projecting 

 articular lip to increase the leverage exerted through 

 the ligament also contribute to make the accident 

 uncommon. 



The later results of these fractures are much influ- 

 enced by the close proximity of the flexor and extensor 



tendons to the region of injury, as, even when the sheaths escape laceration origi- 

 nally, they are liable to become adherent during the process of repair. 



The lower epiphysis of the radius is osseous about the end of the tenth year 

 and is united to the shaft in the nineteenth or twentieth year. The epiphyseal line is 

 almost transverse (Fig. 310), and extends from about nineteen millimetres (three- 

 fourths of an inch) above the apex of the styloid process to six millimetres (one- 

 fourth of an inch) above the lower edge of the sigmoid cavity. The epiphysis is 



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Fracture of lower end ot radius, 

 showing hand carried towards the 

 radial side. 



