The hip joint is a ball and socket joint with the head of the femur or thighbone fitting snugly into a socket in the pelvis. In the dog affected with Hip Dysplasia, these two bones do not fit together with the required degree of correlation. The deep cup of the socket is flattened, so that there is a varying amount of play between it and the femur head. In severe cases the hips are completely dislocated and the dog is crippled and in constant pain. In cases like this the condition can sometimes be relieved by surgery with the removal of the whole femur head. The dog compensates for this by abnormal muscle development and can move fairly normally without pain. Slight cases of H.D. cannot be detected by the dog's movement or behaviour, though there will be arthritic development in the joint as the dog ages. The only method of diagnosis is by X-ray, and this must be done after the dog is a year old before it can be pronounced clear. Very accurate readings are required to detect any slight deviation from normal.

Hip Dysplasia is a term that simply means abnormal development of the hip. This could, of course, have a number of causes, but it is the congenital and inherited defect of the hips, which is causing concern. H.D. is known in cats, horses and cattle and was first recorded in man over two thousand years ago. It was first diagnosed in dogs in 1935 and has since been shown to be widespread, occurring in most breeds of dog irrespective of their size. The mode of inheritance is not completely understood and, in view of the number of breeds involved, there may very well be more than one mode.

Breeding from radiologically clear parents can produce puppies with H.D., though the proportion of affected pups is much smaller than from affected parents. The only method of control is to upgrade our breeding stock by a process of selection.