Inflammation  Hypothesis


		Upon presentation the dog does not demonstrate systemic signs such as a fever that would correlate with the presence of an infectious agent as the source of inflammation. 
	Immune-mediated or rheumatoid arthritis may be indicated as the small and toy breed dogs demonstrate a predilection for rheumatoid arthritis in early adulthood. Rheumatoid arthritis usually presents with a shifting leg lameness (which may be localized to a few joints - in this case the left and right stifle joints) in conjunction with stiffness and pain. Immune-mediated arthritis results when an unknown antigen alters IgG  stimulating a systemic production of an IgM antibody. IgG/anti-IgG and antigen/IgM complexes become fixed in the synovial tissue. When complement attaches to these complexes a chemotactic attraction for neutrophils occurs. As neutrophils enter the joint in higher numbers an inflammatory response results.
	Following inflammation, instability, deformity and laxity develop over weeks to months. This corresponds to the period over which the dog has demonstrated lameness ( a year ago and beginning again 6 months ago)
	 Physical exam results fail to demonstrate other general signs associated with the immune-mediated arthritis such as anorexia, muscle atrophy, generalized lymphadenopathy or cyclic fever. Immune-mediated arthritis fails to explain the medial buttressing of the right stifle.
	Immune-mediated arthritis could be confirmed with radiographs, a joint tap, and joint fluid & serum immune tests to confirm the presence of rheumatoid factor.