336 DISEASES OF THE HOKSE. 



DISLOCATIONS. 



Dislocations and luxations are interchangeable terms, meaning the 

 separation and displacement of the articulating surfaces of the bones 

 entering into the formation of a joint. This injury is rarely en- 

 countered in our large animals on account of the combination of 

 strength and solidity in the formation of their joints. It is met with 

 but seldom in cattle and less so in horses, while dogs and smaller ani- 

 mals are more often the sufferers. 



Cause. — The accident of a luxation is less often encountered in the 

 animal races than in man. This is not because the former are less sub- 

 ject to occasional violence involving powerful muscular contractions, 

 or are less often exposed to casualties similar to those which result in 

 luxa-tions in the human skeleton, but because it requires the coopera- 

 tion of conditions — anatomical, physiological, and perhaps mechan- 

 ical — present in the human race and lacking in the others, which, how- 

 ever, can not in every case be clearly defined. Perhaps the greater 

 relative length of the bony levers in the human formation may con- 

 stitute a cause of the diiierence. 



Among the predisposing causes in animals may be enumerated 

 caries of articular surfaces, articular abscesses, excessive dropsical 

 conditions, degenerative softening of the ligaments, and any excessive 

 laxity of the soft structures. 



Symptoms and diagnosis. — Three signs of dislocation must usually 

 be taken into consideration. They are: (1) An alteration in the 

 shape of the joint and in the normal relationship of the articulating 

 surfaces; (2) an alteration in the length of the limb, either shorten- 

 ing or lengthening; (3) an alteration in the movableness of the joint, 

 usually an unnatural immobility. Only the first, however, can be 

 relied upon as essential. Luxations are not always com,plete; they 

 may be partial, that is, the articulating surfaces may be displaced 

 but not separated. In such cases several symptoms might not be 

 present. And not only may the third sign be absent, but the mobility 

 of the first be greatly increased when the character of the injury has 

 been such as to produce extensive lacerations of the articular ligaments. 



In addition to the above signs, a luxation is usually characterized 

 by pain, swelling, heniorrhage beneath the skin from damaged or 

 ruptured blood vessels, and even paralysis, when important nerves are 

 pressed on by the displaced bones. 



Sometimes a bone is fractured in the immediate vicinity of a joint. 

 The knowledge of this fact requires that we shall be able to diagnose 

 between a dislocation and such a fracture. In this we generally have 

 three points to assist us: (1) The immobility of a dislocated joint as 

 against the apparently remarkable freedom of movement in fracture ; 

 (2) in a dislocation there is no true crepitus — that peculiar grating 

 sensation heard as well as felt on rubbing together the rough ends of 



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