The Forearm. 85 



location at the elbow joint or of a fracture of the humerus, 

 but, should he fall on the palm, with the arm extended 

 sufficiently so as to meet the ground at an acute angle, 

 then the line of impact would pass up in front, i.e., ahead 

 of the forearm, and would probably cause a fracture near 

 the lower end of the radius. In Colles' Fracture the dis- 

 placement of the upper fragment is very slight, whereas 

 the lower fragment is affected to such an extent that in- 

 stead of the articular surface pointing downwards, and 

 slightly forwards and inwards as it normally does, it 

 points downwards, backwards and outwards. 



Causation of this displacement. If the lower end of a 

 radius be examined it will be seen that the posterior bor- 

 der of the articular surface is about % inch deeper than 

 the anterior border, and, further, that the styloid pro- 

 cess projects about % inch from the articular surface. 

 When an injury occurs and a fracture results, the carpus 

 is forced up against the articular surface of the radius, and 

 the lower fragment is ( 1 ) mechanically driven backwards. 

 Again, the more prominent posterior border of the articu- 

 lar surface will receive the impact to a greater degree than 

 the anterior, and hence the lower fragment will be (2) ro- 

 tated backwards, i.e., on an axis passing transversely 

 through it so as to cause the articular surface to point 

 backwards. Lastly, the carpus on forcing the bone back- 

 wards impinges to a greater degree on the outer edge of 

 the articular surface, i.e., on the prominent under surface of 

 the styloid process, and rotates, therefore, the lower frag- 

 ment on a centre which passes vertically up through the 

 styloid process of the ulna, and thus causes the articular 

 surface to point (3) outwards, i.e., towards the radial 

 line. The latter displacement causes the styloid 

 process to be on a higher level than normal, 

 almost, in fact, as high as the styloid process of 

 the ulna. This latter point is of importance, and 



