FEACTUEES OF THE PELVIS. 91 



moderate pronation of the upper fragment, and at the same time 

 it is one which gives the greatest comfort to the sufferer. 



Fractures of the Metacarpals. The metacarpal bones are 

 often broken, either by direct violence, or by indirect force applied 

 at the knuckles. When not impacted, there is a tendency for 

 the two fragments to assume an angular deformity, probably 

 owing to the action of the interossei and the flexors, as well as 

 by the direction of the violence and the weight of the finger. 



FEACTUEES OF THE PELVIS. 



The bones constituting the pelvis have to be looked upon, from 

 a point of view of fracture, both as a whole and individually. 

 As a whole, the sacrum and the two ossa innominata form a 

 complete ring, in which fracture may occur from indirect violence, 

 the circle giving way at its weakest parts. Thus, when a cart- 

 wheel passes over the pelvis of a person lying in the dorsal 

 position, the bony ring is subjected to pressure from before 

 backwards, and consequently the symphysis will tend to approxi- 

 mate to the sacrum. Hence the weak parts of the bones, namely, 

 the rami of the ischium and of the os pubis, on one or both sides, 

 give way. Then, if the compression continues, the iliac bones 

 will be pressed away from the sacrum, but owing to the strength 

 of the sacro-iliac ligaments, either the ala of the sacrum or that 

 portion of the iliac bone immediately external to the articulation 

 is torn away. This, it will be seen, is an evidence of the elasticity 

 of ligaments in contrast with the brittleness of bone. 



On the other hand, should the pressure be upon the pelvis 

 laterally, with the patient lying upon his side, there will be 

 again a tendency for the anterior segment of the ring to give 

 way, and for the two halves of the pelvis to approximate in front, 

 with severe dragging upon the posterior sacro-iliac ligaments, 

 frequently inducing fracture of the lateral mass of the sacrum. 



Another fracture of the hip bone by indirect violence is seen 

 when the acetabulum is broken by the head of the femur being 

 forced against it from falls upon the great trochanter, the violence 

 being transmitted through the neck of the thigh-bone. 



