We hypothesized that it could be a congenital problem because the dog is young and a large breed, owners did not witness a traumatic injury, and the clinical signs are consitent with malformation disorders, such as hip dysplasia.  For example, the dog is uncomfortable when he sits down, it's worse after exercise (which would cause irritation as the poorly fitted elements rubbed against each other), and he's reluctant to walk up the stairs.  Findings on physical exam which were supportive of this hypothesis were subluxation of the hip joint (with no trauma to cause it, this points toward a malformation) and increased joint laxity (positive Ortalani sign).  This sort of disorder could be exacerbated by nutritional problems such as overfeeding.
Jocelyn may be predisposed to bone abnormalities, because of her genetics.  Malformation disorders are more prevalent in large breed dogs.  Jocelyn may have inherited a bad fit between the head of her femur and her acetabulum.  This malformation may account for Jocelyn's joint laxity, which allows inappropriate friction between the bones and the joint capsule, and may cause nerve damage.  The friction may cause damage to the joint capsule, changing the synovial fluid, and compromising nutrition to the cartilage.  This sets up conditions for degenerative joint disease, leading to bony remodeling of the joint.  	
With hip dysplasia Jocelyn may have any of the following: a lack of coverage of the femoral head, a flattened femoral head, osteophytes, and remodeling of the acetabulum.  
A high plane of nutrition can worsen a potential genetic problem by causing the bones to grow faster than normal, and outpace the growth of muscles.  Muscles support the coxofemoral joint in dogs, and as a result, a disparity between bone growth and muscle growth can add to joint laxity.  We think Jocelyn's problem is congenital hip dysplasia, which was made worse by overfeeding.