424 THE INFERIOR EXTREMITY 



direction it comes to the surface on the proximo-medial part 

 of the thigh. 



Intra-Pelvic Spread. When tuberculous disease originates 

 in the acetabulum, it may not only infect the joint but it may 

 spread inwards to the pelvis. The course taken by the pus in 

 the latter case depends on whether it pierces the pelvic wall 

 above or below the line of origin of the levator ani (Fig. 114). 

 In the former case the pus pierces the parietal pelvic fascia and 

 lies in the subperitoneal areolar tissue. It may track along the 

 rectum, or it may fill up the pelvis till it overflows through 

 the obturator foramen or escapes into the thigh behind the 

 inguinal ligament. When it pierces the pelvic wall below the 

 line of origin of the levator ani, the pus at once gains the ischio- 

 rectal fossa and gravitates downwards to point near the anus. 



Owing to the possibility of intra-pelvic spread, digital 

 examination of the pelvis should be carried out per rectum in 

 every case of tuberculous disease of the hip-joint. 



Aspiration of the Hip-Joint can be carried out by intro- 

 ducing an exploring needle upwards, backwards, and medially at 

 a point 2 to 2 1 inches distal to the anterior inferior iliac spine. 

 The instrument gains the interior of the joint by passing under 

 the lateral border of the rectus femoris and piercing the dis- 

 tended capsule. 



The following lines and measurements are of value in the 

 examination of the region of the hip-joint. 



The line joining the highest parts of the two greater tro- 

 chanters passes through the centres of the two acetabula. The 

 head of the femur lies behind the point of intersection of this 

 line and the produced lateral line of the abdomen. 



Nelaton's line, which joins the anterior superior iliac spine 

 to the ischial tuberosity, passes through the highest part of the 

 greater trochanter. When the trochanter is found to lie above 

 or below that line some deformity of the neck of the femur 

 must be present. The difficulty of accurate localisation of the 

 ischial tuberosity minimises the value of this method of 

 examination. 



Chiene demonstrated the symmetry or asymmetry of the 

 trochanters by comparing the line joining their highest points 

 with the line joining the anterior superior spines. This method 

 is of service when the deformity is unilateral, as the lines are 

 then no longer parallel, but it may fail to indicate a bilateral 

 deformity. 



