Hypothesis 3
Inflammation/Infection of Fetlock Joint

	The foal may have an infection of the right rear fetlock joint.  The pitting edema 
seems to support the idea of inflammation.  Foals can be prone to hematogenous 
infections and joints are a common place for these infections to occur.  The foal could 
have had hematogenous spread of an infection and it settled in the fetlock joint.  The 
bacteria could then set up an infection of the joint, with resulting inflammation.  We 
donŐt know if there is heat associated with the pitting edema, which would also support 
inflammatory disease in the foal.  The infection can lead to septic arthritis.   Infection, 
inflammation, and the associated pain could definitely give the foal nonweight-bearing 
lameness.
	There may be damage to the cartilage matrix and chondrocytes.  There is changes 
to the cartilage matrix.  Damage to the collagen fibrils results in decrease in strength and 
an inability to constrain the proteoglycan molecules.  The proteoglycans begin to swell 
which results in swelling of the cartilage as a whole.  The joint is unable to withstand 
normal biomechanical forces.
	The foal, however, does not have a fever, which usually occurs with infections of 
the joint.  Radiographs should be done to rule out osteomyelitis or trauma.  Synovial fluid 
analysis with cytology, Gram stain, and culture and sensitivity should be positive if there 
is an infection of the joint.  Sometimes the culture is still negative even if there is an 
infection.  A blood culture can also be done.