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CHAPTER XIV. 



DlSLOCATIOJvS. 



DISLOCATION OP THE PATELLA DISLOCATION OF THE SHOULDER JOINT 



OTHER DISLOCATIONS. 



A DISLOCATION is the displacement of the ends of bones which 

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

 powtr 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 dithcuities in the reduction of a dislocation arise from the 

 contraction of the muscles— which may be overcome by the influ- 

 ence 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) corresponds to the t nee-cap in hnnian 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 slii)ping 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 invariably 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 

 animals, especially, if they are in a debilitated state, or are out 

 at grass on a rough and hilly country, the nature of which would 

 predispose them to this injury, which, however, may take place, 



