Hypothesis 1 The animal has either congenital or developmental defects resulting in the hind limb 
lameness.

 

Hip dysplasia is the most common congenital defect in large breed dogs affecting the hip joint.  
Hip dysplasia has a heritability factor of .25.  It usually affects large, tall fast growing dogs.  Twenty three 
percent of Rottweillers have hip dysplasia.  Hip dysplasia also has a nutritional component.  The heavier 
the dog is at 60 days the more likely it is that hip dysplasia will occur.   For this reason ad libitum feeding 
is not recommended for large breed puppies.  
The main difference between growth formulas for large breed pups and small and medium breed 
pups is the percentage of crude fat and the amount of calcium/ phosphorous in the diet.  Large breed dog 
diets have a lower percentage of fat and slightly less calcium than small and medium breed diets, however 
the protein content is about the same in both diets.  The reason for less fat is so the large breed pups will 
grow at a slower rate to avoid pathologic changes associated with abnormal bone growth.
	In the case of hip dysplasia, overfeeding will result in premature fusion of the acetabulum.  This 
results in a shallow hip socket, allowing for excessive laxity in the hip joint.
Increased  activity may augment the risk of hip dysplasia. Clinical signs are usually noticed between 3- 8 
months of age.  

Clinical signs for this case are correlate with known cases of hip dysplasia:
Abnormal gait, weight shifted forward, short choppy steps with rear limbs
Pain on flexion and extension
Ortolani sign, decreased ROM
With progression of arthritis, becomes refractory to analgesics or anti-inflammatories
Pain and stiffness when rising from sleep
Pain and stiffness on cold damp days
Crepitation and pain upon extension of joint


Pathophysiology:

Subluxation results in the weight bearing contact area of the femoral head and acetabulum to be reduced.    
This can lead to:
	Rapid wearing of articular cartilage
	Thickening of joint capsule
	Formation of cancellous trabeculae
	Development of osteophytes
Pain is due to degradation of articular surfaces and exposure of subchondral bone nerve endings