ETIOLOGY AND OCCURRENCE 23 



ranges from a simple synovitis to the most active inflammatory 

 involvement of the entire structure and adjacent tissues. 



The reactionary inflammation wiiich attends a case of tarsitis 

 caused b}^ a horse being kieked is a good example of the i-esult 

 of direct injury. Such cases, if the contusion is of sufficient 

 violence, result in arthritis and periarthritis. In inactive farm 

 horses, during cold weather, this condition l)ecomes chronic, swell- 

 ing remains for weeks after all lameness and pain have sub- 

 sided and occasionally hyperthrophy is permanent. 



Arthritis occasioned by indirect injury, such as characterizes 

 joint inflammation from continuous concussion, is seen in horses 

 that are worked at a rapid pace on city streets or other hard 

 road surfaces. Such affections may be acute, as in some cases 

 of spavin, but are usually inflammatory conditions that do not 

 occasion serious disturbance when these affections become chronic. 

 If the involvement persists with sufficient active inflammation, 

 there may follow erosion of cartilage and incurable lameness. 

 If extensive necrosis of cartilage takes place, the attendant pain 

 will be sufficient to cause the animal to favor the diseased part 

 and such immobilization enhances early ankylosis — nature's sub- 

 stitute for resolution in this disease. 



Wounds invading the tissues adjacent to joints, when these 

 wounds are of considerable extent, cause inflammation of such 

 articulations by contiguous extension of inflannnation. As long 

 as an injury remains practically aseptic, or if infected and the 

 septic process does not involve the joint proper by direct ex- 

 tension, no more serious disturbance than a simple synovitis will 

 result. If, instead, a periarthritic inflammation is serious or 

 destructive in character, the type of arthritis will be grave — 

 even though due to an indirect cause. 



Where a vulnerant body penetrates all structures and invades 

 the interior of the joint capsule the result is that a more or less 

 active disturbance is incited. The introduction of a sterile in- 

 strument into a joint cavity, under strict asepsis, where a per- 

 fect technic is executed, does not cause perceptible numifesta- 

 tion of the injury, if the opening so made is small — such as a 

 suitable exploratory trocar makes. But a puncture made in a 

 similar manner and with the same instruinciit witliout due regard 



