294 



HUMAN ANATOM 



^ 



B 



per cent, of all surgical cases in children under six years of age, and is believed to 

 depend on a distinct anatomical lesion, the exact nature of that lesion is still un- 

 known. It is usually caused by traction on the forearm. The most plausible of 

 many theories are : ( i ) that it is due to the head of the radius slipping out from 

 beneath the orbicular ligament, which is pinched between it and the capitellum (Fig. 

 311) ; and (2) that it is a partial epiphyseal separation. The differential diagnosis is 

 said to depend chiefly on the facts that in the " subluxation" the head of the radius 

 will rotate with the shaft, and that all the symptoms disappear rapidly after forced 

 supination has removed the functional disability. There seems nothing absolutely 

 inconsistent with these symptoms in the view that a slight epiphyseal separation has 

 occurred, the upper end of the diaphysis being displaced forward, but carrying with 

 it the radial head. This theory is strongly favored by the fact that very few cases 

 have occurred in children over five years of age. Ossification of the radial head 

 begins towards the end of the fifth year. It should be remembered that the epiphy- 

 sis includes only the upper part of the head, the lower portion and the neck being 

 ossified from the shaft. The upper end of the diaphysis is therefore approximately 

 of the same size and shape as the head, and may easily have been mistaken for it in 



many of the cases. The problem pre- 

 FiG. 308. sented is so purely an anatomical one 



that, in spite of the prevalent differences 

 of opinion, it seems proper to make this 

 brief presentation of it. 



Fractures of the head are uncom- 

 mon. Fractures between the head and 

 the lower end will be considered in refer- 

 ence to the effect of muscular action upon 

 them (page 604). 



In the neighborhood of the tubercle 

 the thickness of the bone, the ridges that 

 run up towards the head and down 

 towards the outer edge, and the ample 

 covering of muscles render fracture com- 

 1 1 / i paratively uncommon. A little lower the 



union of the two secondary curves near 

 the point of greatest curvature in the 

 primary curve of the whole shaft renders 

 the bone more vulnerable. Still lower 

 the effects of indirect violence through 

 falls upon the hand, the union near the 

 lower end of the compact tissue of the 

 shaft with the cancellous tissue of the 

 • expanded lower extremity, the compara- 

 tively superficial position of the bone, 

 and the projection of the anterior articular lip, into which the anterior carpo-radial 

 ligament is inserted, all very markedly favor fracture. 



Accordingly, we find that, on account of these anatomical conditions, of one 

 hundred fractures of the radius, approximately, three will be in the upper third, 

 six in the middle third, and ninety-one in the lower third, the large majority of 

 these latter being within from 2.5 to 5 centimetres (one to two inches) of the wrist- 

 joint. 



Fractures of the lower end of the radius are almost always produced by a 

 cross-breaking strain caused by falls on the hand, and exerted through the strong 

 anterior common ligament. The broad attachment of this ligament to almost the whole 

 anterior lip of the radius brings the strain equally on the bone through its entire width. 

 The fracture is, therefore, usually irregularly transverse. In addition to the force 

 transmitted by means of the ligament, there is an approximately vertical force, due 

 to the weight of the body, which thrusts the sharp lower end of the shaft into the 

 lower fragment, made up chiefly of spongy tissue, with merely a thin shell of com- 

 pact tissue holding it together. This vertical force transmitted through the forearm 



1 



Lines of fracture of neck and of lower end of radius 

 (Colles's fracture). A, dorsal ; B, lateral aspect. 



