Injury Hypothesis

This dog is still a puppy and due to its bounding energy, we would expect an injury that could lead to lameness.  This is a large breed dog and the weight and force that the dog lands with might have lead to a stress on the hip joints hence the hind-limb lameness, and subsequent pain.  The children in the family might have been playing rough with the dog causing an injury that went unnoticed by the owner.  This trauma can cause the ligaments and cartilage around the hip joint to tear and destabilize the joint. This results in increased laxity of the joint.  The femoral head has increased contact with the acetabulum and there is increased pressure on the femoral head and synovial joint.  This can cause pressure necrosis on the fibrocartilage joint capsule.  As a result of that damage there is joint effusion and localized inflammation.  The mediators of inflammation, such as prostaglandins and bradykinins initiate a pain response.  Pain can also be caused due to nerve compression and damage.  Because of the pain in the hind limb, the dog is reluctant to walk up and down stairs and has trouble sitting and standing.  The dog is also compensating for this pain by putting most of its weight on the forelimbs. Because the coxofemoral joint is no longer properly aligned, the range of movement for the leg is decreased.