LUXATION OF THE SACRO-ILIAC JOINT 87 



is bounded superiorly by the free portion of the inferior edge of the 

 great sacro-sciatic ligament — i.e., that portion of the edge which is 

 situate between the superior ischiatic spine and the tuber ischii. Its 

 inferior boundary is formed by the outer border of the ischium. The 

 common tendon of the obturator internus and pyriformis muscles passes 

 out from the pelvis by this foramen. 



The sacro-iliac joint possesses a synovial membrane which lines 

 the sacro-iliac ligament. The membrane secretes a scanty amount 

 of synovial fluid. 



The movements of the joint are very restricted, and consist only of 

 a very slight antero-posterior gliding. The use of the joint appears 

 to be to restrict the concussion to which the bones of the part are 

 subjected during propulsion of the body. Anchylosis of the joint 

 occasionally takes place, when the bones are rendered very much more 

 liable to be fractured. 



LUXATION OF THE SACRO-ILIAC JOINT 



From the anatomical description of this joint it will be readily 

 understood that luxation is very rare. This is on account of the firm 

 manner in which the bones are united to one another. It is so firm, in 

 fact, that the ilium is much more likely to be fractured than the joint 

 dislocated. 



Luxation is occasionally met with in colliery ponies, as a result of a 

 heavy fall of roof on to the region of the croup. In these cases there is 

 little difficulty in diagnosis, on account of the marked alteration in the 

 conformation of the part. 



The sacrum is pressed downwardly, and the internal angles of the 

 ilium are much more distinct, forming sharp, prominent bulgings. which 

 may be easily felt, and which appear to be subcutaneous. That there is 

 no fracture of the ilium may be ascertained on manipulation, which is 



