314 



CHAPTER XIV. 



Dislocations. 



dislocation op the patella dislocation op the shouldbe joint 



other dislocations. 



A DISLOCATION is the displacement of the ends of bones which 

 form a joint. Its chief symptoms are : deformity, decreased 

 power of movement, and pain. If fracture exists at the same 

 time, the power of movement in the part may be increased, with 

 the existence, however, of alteration in the shape of the joint. 

 The difficulties in the reduction of a dislocation arise from the 

 contraction of the muscles — which may be overcome by the 

 influence of chloroform — and from mechanical impediments in 

 the part. 



Dislocation of the Patella. 



Although this is a rare accident, it is the most common form of 

 dislocation which occurs in the horse. 



The patella (Fig. 115, p. 297) corresponds to the knee-cap in human 

 anatomy. It is placed in front of the stifle joint, which is formed by the 

 femur and tibia, and affords attachment and increased leverage to certain 

 muscles, the office of which is to bring the hind leg forward. In order to 

 keep the patella in its place, it is connected to the tibia, by three straight 

 ligaments which antagonise the muscles in question ; and there are two 

 lateral ligaments — an internal and an external — ^which prevent it from 

 slipping to one side or the other. The portion of the femur on which the 

 patella works, is pulley-shaped, with two prominences and a groove between. 

 As the internal prominence is larger and projects more to the front than 

 the external one, the patella, when dislocation takes place, is almost in- 

 variably displaced to the outside. 



Foals, on account of the comparative want of tenacity of their 

 ligaments, are much more liable to this accident than are older 



