Hypothesis 3- Endocrine/Genetic disorder predisposing to 
weakened joint structure

Bonnie seems to get a moderate to extensive amount of exercise 
(two 30-60 minute walks per day, 3 mile jogs a couple of times a 
week, weekend walk in the woods and playing fetch during lunch 
breaks). She is receiving 4 cups of Hills Science Diet Adult 
Maintenance dog food.  While we do not know Bonnie's exact 
weight, we believe it is probably between 80-90 pounds.  She 
should be receiving approximately 4.5 cups of food each day. 
Thus, it does not appear that Bonnie is being overfed, unless the 
owner is not providing accurate information on the amount of 
treats Bonnie is receiving. Therefore, it is hypothesized that 
because Bonnie receiving adequate exercise and food, but is still 
overweight, she may have an endocrine or genetic disorder that 
might predispose her to joint weakness due to excess stress placed 
on her joints due to excessive weight.  

One possible explanation is hypothyroidism, while we only have 
limited information, it is possible that given Bonnie's seemingly 
excessive amount of exercise and normal food intake she may have 
a deficiency in thyroid hormones. Hypothyroidism would decrease 
her metabolic basal rate and thus allow her to maintain excess 
weight even though she receives enough exercise.  Thus, with 
increased weight placed on BonnieÕs joints, it is possible that the 
increased stress may have predisposed her to possible joint 
damage/cartilage degradation which could then lead to 
degenerative joint disease.

Another possibility is hyperadrenocortisolism(CushingÕs Disease).  
CushingÕs may be associated with a degree of osteopenia.  
Corticosteroids are thought to have a direct effect on bone, 
inhibiting both osteoblasts and osteoclasts. The overall effect is to 
increase bone resorption. In addition, corticosteroids increase the 
ÒstickinessÓ of platelets, which coalesce, causing thrombosis of 
vessels within bone.  This leads to reduce bone blood flow and 
blood stagnation within bone, resulting in an elevation of blood 
carbon dioxide. This in turn stimulates osteoclastosis.  
Occasionally in dogs with Cushing's Disease, profound muscle 
weakness is noted and the dog may have difficulty when rising or 
may have difficulty when standing for long periods of time.  
Chronic hypercortisolism, may result in exaggerated response to 
common problems such as cranial cruciate ligament tears.

Yet another possibility is Factor VIII deficiency or hemophilia A 
which can lead to an arthropathy that is caused by hemorrhage into 
the joint, induced by an episode of trauma.  The larger weight-
bearing joints, such as elbows and stifles, are more likely to be 
involved.  Larger, more active dogs (like Bonnie) experience a 
higher incidence.  There are three types of arthropathy associated 
with this disorder. There is an acute stage, subacute and chronic 
stage. The acute stage is characterized by a hemarthrosis producing 
a swollen and painful joint.  The subacute stage develops after 2 or 
more acute episodes and may show an inflammatory reaction 
within the synovium.  The chronic stage is characterized by bone 
and cartilage destruction.