DISEASES OF THE BONES, JOINTS, AND TEETH 211 



sKorter than the other and a permanent lameness results, or a 

 "false joint" forms. 



The "knitting" of a fractured bone differs little from the healing 

 of wounds of the skin. A jelly-like substance is poured out from 

 the injured ends. By the action of certain cells this substance soon 

 turns to gristle and forms a callus, or bony enlargement, which com- 

 pletely surrounds the fracture and firmly welds the ends together. 

 Cells from the periosteum and bone-marrow play the most impor- 

 tant role in uniting a fracture. The administration of small doses 

 of phosphorus assists callus formation. 



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 of 

 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- 

 rary or complete and permanent. The horse is said to be "stifled" 

 when this accident occurs. Slipping when getting up in the stall, 

 and stepping down from the stable floor to the ground some inches 

 lower, are movements that may cause the patella to slip out of 

 position. It may either snap back into place as soon as the joint 

 is flexed, or catch and remain stationary at either the upper or 

 outer side of the trochlea. In some cases it shps in and out with 

 every step without preventing locomotion, but rendering the ani- 

 mal worthless, if long continued, by bringing about excessive 

 wear on the articular cartilages. In upward dislocation the stifle 

 joint is abnormally extended, which causes the leg to become rig- 

 idly stretched backward and makes progression almost impossible. 

 Even with assistance the horse cannot bring the leg forward. By 

 suddenly moving the animal backward and to the side the bone 

 may shp back into position. If this is unsuccessful, place a rope 

 around the pastern and lift the toe forward and upward; at the 



