Hypothesis ThreeÑARTHRITIS

ARTHRITIS associated with the stifle joint.

Canine rheumatoid arthritis- Manifests initially as a shifting leg lameness, 
with soft tissue swelling around the involved joints in following weeks or 
months. 
	Pathophysiology- Normally localized to a few joints as seen here in stifle and tail vertebrae.  
After localization into individual joints characteristic radiographic changes develop.  Earliest 
radiographic changes show soft tissue swelling and loss of trabecular bone density in area of joint.  
Lucent, cyst-like areas are frequently seen in the subchondral bone.  Prominent lesion is progressive 
erosion of cartilage and subchondral bone in the area of the synovial attachment which results in loss 
of articular cartilage and collapse of joint space.  Angular deformities often occur and luxation of joint 
is frequently a sequelae. Deformities are most common in carpal, tarsal and phalangeal joints and less 
frequent in elbow and stifle.  
	Synovial fluid changes indicate a sterile inflammatory synovitis with 
increase in total cell count and a high proportion of neutrophils in the 
synovial cell population.  Condition is believed to be due to deposition of 
immune complexes in the synovium. Antigens stimulate Ig-M and this results in 
the deposition of immune complexes in the joint.  Complement attaches to these 
complexes which attract neutrophils which cause tissue damage resulting in 
inflammation.


 
Osteoarthritis is a disease that is very common as a secondary lesion, but it my 
also be a primary lesion when there is an inherited abnormality of cartilage 
components. Osteoarthrits is usually subsequent to trauma.  It is initiated by 
damage to the chondrocytes.  The damage increases the production of 
metalloproteases and the release of inflammatory mediators.  This causes the 
breakdown of proteoglyacans and collagen.  Free collagen fragments are released 
into the joint capsule, resulting in thickening of the capsule.  As the 
cartilage is broken down, subchondral bone experiences more stress and 
subsequently thickens.  Once the subchondral bone is affected, the condition is 
self perpetuating and irreversible.  Inflammation usually results in joint 
effusion due to the increased permeability of synovial vasculature.

Systemic Lupus associated arthritis-this is seen with a polyarthritis and 
dermatitis, and this animal is being treated with Benadryl for skin problems.  
The clinical signs are episodic, as seen here.  There is usually depression, 
anorexia and fever.  It is an immune mediated disease caused by a loss of 
control over B cell production and activity.  The B cells produce anti-nuclear 
antibodies which form immune complexes that deposit in the synovia to cause 
arthritis.  This disease is usually seen in middle-aged dogs (this patient is 3 
years old) and the most common clinical sign is symmetrical nonerosive 
polyarthritis.  To make a diagnosis of SLE, the dog must have 2 clinical signs 
(this dog has skin lesions and bilateral joint pain, possibly indicative of 
polyarthritis) and a positive ANA test.  

Note:  Arthritis may also occur secondary to any inflammatory or infectious 
disease.


 Septic Arthritis- Frequently associated with bacterial agents such as Staph. 
Strep. or coliforms.  Causes include hematogenous spread or surgery (iatrogenic 
causes), failure of passive transfer, spread from adjacent osteomyelitis, RMSF, 
Ehrlichiosis and spirochetes (borreliosis).  Clinical signs include: Lameness, 
swelling, pain in affected joints and systemic signs of fever, malaise, anorexia 
and stiffness.  Radiography may reveal joint effusion in early cases and DJD in 
chronic conditions.  Athrocentesis will reveal WBCÕs, especially neutrophils.  
Synovial fluid may be grossly purulent