5G DISEASES OF THE SYNOVIAL MEMBRANES AND ARTICULATIONS. 



III.— LUXATION OF JOINTS. 



Luxation consists of permanent displacement of the bony surfaces 

 forming a joint, and may follo^Y violent mechanical injury or any 

 other cause. 



Luxations have been divided into congenital, i.e., such as exist from 

 the time of birth ; spontaneous, i.e., those which result from some defect 

 of conformation or constitution ; and acquired or accidental, which occur 

 as results of falls, wounds, accidents, etc. 



From the point of view of their duration, luxations are termed 

 temporary when they do not necessitate reduction, progressive when 

 the tendency is towards greater and greater displacement of the surfaces, 

 or permanent when reduction is impossible. 



Those commonest in bovines are luxations of the femur, luxation of 



the patella, femoro-tibial luxation, and luxation of the scapulo-humeral 



joint. 



LUXATION OF THE FEMUR. 



Luxation of the head of the femur with displacement beyond the 

 cotyloid cavity is very frequently congenital. The condition also occurs 

 with some frequency in adults or aged animals in consequence of 

 relaxation of the articular ligaments and the absence of the subpubic 

 ligament (pubio-femoral ligament). 



Causation. Luxation may be congenital, the head of the femur 

 being displaced backwards and carried above the cotyloid cavity. This 

 form is of no jjractical interest, because the animals are not usually 

 reared. More frequently in young or adult animals it assumes the 

 spontaneous progressive form, in consequence of degenerative changes in 

 and relaxation of the coxo-femoral interosseous ligament. The head of 

 the femur presses on the upper margin of the cotyloid cavity, which it 

 injures, and eventually becomes lodged in the neighbourhood of the neck 

 of the ilium, in the great sciatic notch. 



This luxation is also found as a purely accidental occurrence in 

 animals which have suffered from falls and from slipping of the hind 

 limbs backwards or sidewards, as occasionally follows awkward leaping 

 movements. The slipping outwards of the limbs, which causes this form 

 of luxation, is comparatively easy, because of the absence of the pubio- 

 femoral ligament. The accident may also be followed merely by 

 subluxation, that is to say, tearing of the inner portion of the capsular 

 ligament and rupture of some portion of the adductor muscles of the 

 thigh without rupture of the interosseous fibres, the head of the femur 

 not quitting the cotyloid cavity. This accident occurs in stables with 

 smooth, slippery floors, and in railway trucks. It may affect one side 

 or both. The latter condition is exceptional. 



