DISEASES OF THE BOWES AND JOINTS 



295 



stance soon turns to gristle and forms a callus, or bony enlarge- 

 ment, which completely surrounds the fracture and firmly welds 

 the ends together. Cells from the periosteum and bone-marrow 

 play the most important role in uniting a fracture. The adminis- 

 tration of small doses of phosphorus assists callus formation. 

 ! 



Fig. 75. — Large pasterns of same horse. The specimen at the left is normal, 

 the one at the right shows a knitted comminuted fracture. Note how the frac- 

 ture shortened the bone. 



JOINT DISEASES 



All joint diseases are accompanied with inflammatory changes. 

 The term arthritis is used in a broad sense to denote any form of 

 joint inflammation. Serous arthritis is the most common form in 

 mature horses. In foals suppurative arthritis is more frequently 

 seen, as it results from navel infection. 



The most frequently occurring joint diseases are dislocations, 

 sprains, deforming arthritis, and overfilling of the joint capsules 

 with synovial fluid. Any freely movable joint may become af- 

 fected. As the stifle, hock, and fetlock joints are most often the 

 seats of these diseases, they will be taken as types for illustration. 



Dislocation of the patella is displacement of this bone from 

 the trochlea of the femur. It may be either partial and tempo- 



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