DIAGNOSIS:   BILATERAL HIP DYSPLASIA

     The diagnosis of bilateral hip dysplasia was attained based on collective information gathered in the 
history, physical exam, radiographic exam, orthopedic exam and diet evaluation. Hip dysplasia is the 
abnormal development of the coxofemoral joint characterized by subluxation (evident in this case) or 
complete luxation of the femoral head; varying degrees of degenerative joint disease may be seen, 
depending on the age of the dog. This condition is painful to the animal because wear of articular cartilage 
exposes pain fibers in subchondral bone.
     The history of this patient disclosed several facts pertinent to this diagnosis. The rottweiler is considered 
a large breed dog, which places it in the high risk category for developing this disease. One reason for this 
genetic predisposition is that the epiphyseal spongiosa of giant breed dogs is less dense, and therefore 
weaker, than smaller breeds. The clinical signs of awkward gait, worse in the morning and after exercise, 
and that the dog cannot get up the stairs are all consistent with the types of symptoms you would expect to 
see with this condition. At an age of 9 months, the growth plates are still open, which also increases the 
chance of a developmental orthopedic disease. 
     The physical exam revealed several facts which isolated the problem to the coxofemoral joint, as 
palpation of the hip joint produced a pain response, whereas the hock and stifle joints were normal. No 
muscular pain / atrophy of the rear limbs, combined with the absence of any neurological deficits 
eliminated the possibility of a muscle or nerve etiology of the lameness.  The orthopedic exam established a 
reduced range of motion of the hip (130 degrees), as well as a positive Ortalani sign, which indicated hip 
laxity (looseness). Both of these findings point towards a coxofemoral joint abnormality.
     The radiographic exam revealed a subluxation of both the right and left coxofemoral joints, a sign which 
is strongly suggestive of hip dysplasia. Subluxation stretches the fibrous joint capsule, and can produce 
pain and lameness. The cancellous bone of the acetabulum can become deformed by continued dorsal 
subluxation of the femoral head. In this case, however, very few degenerative joint changes were visible on 
the radiograph, indicating the disease is early in its pathogenesis. A subluxation also decreases the area of 
articulation, which concentrates the stress of weight bearing over a small area in the hip joint. Premature 
wear of the articular cartilage uncovered pain fibers, which lead to the lameness present in this dog. 
     Nutrition is considered to be one of the major factors predisposing large breed dogs to hip dysplasia. 
Excesses in energy, fat, and calcium can all lead to developmental bone disease. In this particular case, the 
9 month old dog is being fed free choice, which is producing a larger than ideal feed intake. Additionally, 
the dog is on an adult maintenance food, where at the age of 9 months a Rottweiler is still growing, and 
should be on a large-breed growth diet. Although the exact implications of nutrition on pathophysiology of 
this disease are not known, there are two current theories connecting nutritional problems to hip dysplasia. 
     The first theory involves energy, growth, and biomechanical stress. The skeletal system is most 
susceptible to physical, nutritional, and metabolic insults during the first 12 months of the animal's life. 
High energy intake directly affects the growth velocity through nutrient supply, and indirectly by way of 
changes in the concentrations of growth hormone, T3, T4, and insulin. Abnormalities in these hormones 
can alter the normal environment for joint development in the young dog. Growth hormone stimulates 
chondrocyte production and differentiation into cartilage. Free choice feeding, as we have in this particular 
case, has been associated with increases in circulating T3 and T4. These two thyroid hormones are involved 
in increasing the rate of bone formation and resorption, as well as capillary penetration of degenerating 
cartilage cells and the final stage of endochondrial bone formation. The overall result of these hormonal 
influences is hyperproliferative cartilage cells, which may enlarge the width of the zone of chondrocyte 
growth in the coxofemoral joint. Free choice feeding may ultimately lead to abnormal ratio between bone 
growth and body growth, increasing the likelihood of a joint disorder.
     The second theory suggests that an excess in calcium intake can predispose a dog to developing hip 
dysplasia. Large breed dogs fed a diet with high calcium content (1.2% or greater) have been shown to 
develop abnormal endochondrial ossification, and delayed skeletal maturation and growth of bone length. 
Large breed growth formulations are designed to have a lower calcium component in an attempt to prevent 
developmental orthopedic disease. Iams Large Breed Maintenance, however, has a calcium content of 
1.2%, implicating calcium as a possible factor in the development of hip dysplasia in this dog.