Subchondral Bone neoplasia below the cartilage of the femoral head

Invasion of neoplastic osteophytes into articular cartilage causes 
disruption of cartilage integrity. This may lead to acute 
inflammation of the cartilage as it attempts to repair the insult
The response in the joint to this inflammation results in pain and 
loss of function.  The space occupying mass at the cranial portion 
of the femoral head of the right hind limb would cause pain during 
motion.  This pain would cause the left limb to compensate and 
therefore becomes sore as well but not as severe as the primary 
lesion.  During exercise the lesion abrades the articular surface 
causing increased inflammation and discomfort.  The condition did 
not improve with Rimadyl therapy because the neoplasia itself causes 
pain upon motion while Rimadyl would only reduce inflammatory 
responses.  The location of the neoplastic lesion does not interfere 
with the function of any nerves or muscles therefore no deficits 
were seen in these areas. Neoplasia can be spontaneous and would not 
need a traumatic incident to occur.  Joint effusion has not yet 
occurred because the magnitude of the inflammatory response has not 
yet reached a level to cause effusion.