In basic terms hip dysplasia is the improper growth of the hip joint. This can lead to the hip moving and this in turn, over time, can result in arthritis also called degenerative joint disease, arthrosis, osteoarthrosis. It can be a very painful condition. Although it is more normal for large breeds to be susceptible to CDD, medium and even small breeds can develop the condition; the Orthopedic Foundation for Animals is an organisation that keeps a database of many canine conditions including CHD the Pug (a toy breed) is ranked the second worst with 63.8% of those tested (390 tests) being dysplastic and yet at the other end of the height spectrum the Borzoi ranked #157 with only 1.8% having a dysplastic result.
Damage caused to the cartilage that lines the hip joint, which results in CHD, may be onset by the result of trauma or it can be caused by inherited defects; an abnormally developed hip joint. When the cartilage is afflicted various enzymes cause a process which results in the cartilage loosing its thickness and elasticity. This thickness and elasticity has the important job of absorbing the loads placed on the joint during movement e.g. rising, running, walking etc. The degeneration is progressive and the enzymes and other debris spill into the joint lubrication fluid. This results in the joint be inadequately lubricated and the cartilage not receiving the nutrients it requires. As the cartilage gets thinner it eventually allows the synovial fluid to make contact with nerve endings which causes pain. In some cases to counter-act this the dog's body produces new bone around the edges of the joint (spurs) and this added bone can cause the range of motion in the joint to be decreased and additional pain.