THE HIP-JOINT 427 



aim of the surgeon is to obtain a stable joint. If a movable 

 joint can be obtained at the same time, the result will be so 

 much the better, but mobility without stability is of no value. 



The weight of the trunk is transmitted to the femoral heads 

 through the upper parts of the acetabula, and thence is trans- 

 mitted down the limbs to the ground. 



In order to increase the power and mobility of the lower 

 limb and to distribute the weight of the body over a wider base, 

 the neck of the femur is inclined to the shaft at an angle which 

 varies from 160 in the child to 110 in the adult, i.e. with the 

 constant increase in body-weight the angle deviates more and 

 more from 160. 



Abnormal alterations of the angle may seriously interfere 

 with the mobility of the hip-joint. In cases of early extensive 

 infantile paralysis of the lower limb, and in congenital dislocation 

 of the hip, the angle remains of the infantile type, since the 

 head and neck of the femur are not used to support their share 

 of the body-weight. This condition is known as coxa valga. 



In constitutional diseases, such as rickets, and following 

 injuries to the neck of the femur during infancy, the body- 

 weight acting on softened bone produces an abnormal decrease 

 of the angle, which in some cases may be reduced to 45. This 

 condition is termed coxa vara. 



Abduction of the thigh is markedly limited in coxa vara, 

 as the greater trochanter impinges too soon on the ilium. In 

 coxa valga, on the other hand, abduction is a very free movement, 

 but adduction is correspondingly limited. 



Injuries of the Neck of the Femur. In the infant, the 

 cartilaginous proximal extremity of the femur, which includes 

 both the head and the neck, may be fractured. The injury 

 often occurs in the following way. When an infant, held in 

 the nurse's arms, throws itself backwards, the weight of its body 

 stretches the strong ilio-femoral ligament across the anterior 

 surface of the head of the femur. If the child's limbs 

 were not held by the nurse the pull of the body-weight on the 

 ligament would flex the thigh and relieve the strain, but as 

 the limbs are firmly held, the cartilaginous neck of the femur 

 gives way, since the ilio-femoral ligament is too strong to yield. 



In the child, injury in this region may result in a green-stick 

 fracture, as the cartilaginous neck is undergoing ossification. 

 Radiograms have shown that this accident is by no means rare, 

 and it is probably one of the most frequent causes of coxa vara. 



