360 The Pelvis 



PART V 

 THE PELVIS 



The innominate bone has three primary centres of ossification : 

 for ilium at third month of foetal life, ischium at fourth, and pubes at 

 fifth. During childhood these segments are 

 joined in the acetabulum by a Y-shaped carti- 

 lage, which, becoming softened and disinte- 

 grated in hip-joint disease, readily allows pus to 

 work through into the pelvis. 



Five secondary centres appear at puberty : 

 in the Y-shaped cartilage (so that the three 

 parts of the bone are soon after fused together) ; 

 in the iliac crest, which, as a cartilaginous rim, 

 is sometimes detached by violence ; in the 

 anterior inferior iliac spine, which may be torn 

 off by energetic contraction of the rectus 



femoris, or by direct violence ; in the ischial tuberosity, and at the 

 pubic symphysis. The bone is welded into a solid mass at about the 

 twenty-fifth year. 



Weaver's bursa The ischial tuberosity is separated from the 

 gluteus maximus by a large bursa, and in those who sit much, as 

 weavers, tailors, and coachmen, the sac may become inflamed, and may 

 suppurate. 



The sacro-iiiac joint is formed by the auricular surfaces of the 

 sacrum and ilium, each of which is covered with a layer of cartilage. 

 The anterior sacro-iliac ligament is thin, the posterior is thick and 

 strong, and, in addition, contains a large amount of interosseous fibres. 

 The joint is supplied by branches of the gluteal and ilio-lumbar arteries, 

 and by nerves from the superior gluteal, the sacral plexus, and perhaps 

 from the obturator. 



Disease of the joint may follow injury, or parturition, or may be 

 secondary to spinal caries. The local tenderness may be detected by 

 following the iliac crest round to the sacrum, and pressing below the 

 posterior superior spine. 



In addition to the constant pain at the bottom of the back, there 



