Joint inflammation could cause the hip pain felt by this patient.  There are many 
possible etiologies of joint inflammation, but these are broken into two main categories; 
infectious and immune mediated.  Infectious joint inflammation is the result of sepsis, 
when blood borne bacteria spread to highly vascularized joint cavities.  Non-septic 
immune mediated joint inflammation can be associated with neoplasia, chronic infection, 
canine rheumatoid arthritis, or idiopathic.  
	In this specific case, septic joint inflammation seems unlikely.  The patient does 
not show clinical signs associated with sepsis.  However, a blood culture and joint 
tap/culture could be performed to definitely rule this out.  The most common cause of 
erosive immune mediated inflammation is canine rheumatoid arthritis, however this 
generally affects more distal joints first; this seems an unlikely etiology in this case.  The 
most likely cause for the possible joint inflammation of the patient may be nonerosive 
immune mediated arthritis.  This results when antigen/antibody complexes are distributed 
in synovial fluid, which initiates the inflammatory cascade.
	Regardless of the cause, the mechanism of joint inflammation remains constant.  
The first step involves changes in the microcirculatory system, such as and increase in 
small vessel permeability and arteriolar dilation.  At this point white blood cells and other 
inflammatory mediators, including macrophages, neutrophils, and complement, are 
disrtibuted into the synovium.  A swelling of the synovium would disrupt the normal 
joint alignment, causing improper joint articulation and pain with movement.