Hypothesis 2 :		INFECTIOUS


	This foal could possibly have a bacterial/viral infection obtained through 
the 
umbilical cord.  This could be a systmeic infection that has localized in the 
fetlock joint.  An infection in the joint is the inoculation of the synovial 
membrane or fluid with bacteria or other organisms that cause the inflammatory 
reaction.  The inflammatory reaction causes heat and pain.  In order for the 
bacteria to establish an infection, it must be able to bind to the tissues of 
the joint and establish growth. A healthy synovial membrane is usually capable 
of controlling a large number of bacteria and therefore not allowing bacterial 
proliferation.  Due to the young age, the degree of joint destruction was rapid 
and the foal was not able to control the bacterial numbers.  The tufts of the 
synovial capillary favor entrapment and localization of bacteria in the synovial 
lining.  

	Once the bacteria have colonized the joint, a series of events takes 
place.  This results in loss of proteoglycan and collagen from articular 
cartilage.  Rapid cartilage destruction is the sequela and the body is racing to 
correct these problems prior to the hallmark of osteoarthritis which is 
irreversible and progressive.  Due to the synovial membrane inflammation, 
hyperplasia, and fibrosis there is a decrease range in motion and often pain.  
This is why the foal resisted palpation. As the body lays down fibrin to help 
amend the problem, the fibrin is compromising the synovial membrane function and 
cartilage nutrition.  

This septic joint infection is probably hematogenous in origin.  The 
umbilicus could be the portal of entry.  This could be an extension of 
osteomyelitis.  This is supported by the proximal swelling of 12cm. 


 	The infection leads to chemotaxis  and the 
filtrate of inflammatory cells leads to edema.  Because the mare is currently 
vaccinated 
and the foal received colostrum, it is unlikely that the foal inherited an 
infection from the 
mare.  The foal is more susceptible to infection due to the young age and the 
lack of time 
to build sufficient immunity.  A simple injury, trauma, or umbilical infection 
could have 
potentially devastating effect.