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Hip Dysplasia
Genetic or Environmental?

M.C. Wakeman, D.V.M.

One frequently encounters discussions which assert that hip dysplasia is 50% genetics and 50% environment. We prefer to think of it as 100% genetics, then 100% environment. Genetic considerations are the entirety of what we must as breeders consider. Once that puppy is born, environment is 100% of how well that puppy will do within the possibility of his genetics. Dogs with very good hips, congenitally, may have an injury and end up diagnosed as having 'unilateral hip dysplasia'. Individuals with very shallow sockets may be mobile and free of pain to an advanced age, if they have unlimited exercise. This is the entirety of what the owner of that puppy needs to concern himself with to provide the best possible care for his dog.

Over the years, our observations of the kennel populations of giant breeds and their siblings living in private homes have led to the conclusion that there is no such thing as congenitalunilateral hip dysplasia, but only acquired unilateral hip dysplasia. The kennel dogs, whose exercise opportunities are maximized, with several dogs of a similar age free to run and play all day and night in large paddocks, show us some interesting things.

Their litter mates in private homes, where exercise is confined to an hour or two of intense play or jogging when their owners return from work, provide us with a different set of observations. The implications of these observations are enormous, but very simple to understand. These large breeds grow much too quickly for their biology to keep up. They frequently show some degree of clinical rickets with some bowing of the forelegs, and have large soft joints due to the inability of the body to deposit calcium in the bone at a rate equal to the rate of growth. They often show uneven growth, with the rear end growing over a few weeks, then the front end trying to catch up. As the rear leg assembly grows disproportionately, and the puppy is 'high in the rear', the mechanical leverage that the muscles are able to exert across these straighter angles is much reduced. The result of this is a decreased ability of muscle to protect joints from injury.

The owners of giant breed pets tend to overfeed their puppies, having with the best of intention, the inner desire to see a 'big dog' and to do nothing which might risk the dog not attaining the greatest possible size. Try as they may, some owners are just unable to restrict their puppy's diet. Owners are cautioned that their puppy needs a good deal of exercise, but their work schedules often conflict with their desire to do this. The result is a period of intense exercise. A 3 mile run, or a half hour of Frisbee. When a single puppy who lies around all day welcomes his owners in the evening, he is ill prepared for either intense exercise, or the uncertainty of footing on slippery floors and his always changing joint angulation. His muscle tone is a small fraction of that of a puppy which plays with other active dogs all day long. The result is an injury.

When any dog has a hip dislocated, if it is not repaired within 48 hours, the socket begins to lose depth. When an injury occurs to a rear leg, whether it be a toe injury, a stifle injury, a soft tissue injury, or a hip injury, the result is often a decreased amount of weight bearing on that leg over a period of days to weeks or months. When this happens, the mechanical forces applied to the living bone tissue change, and the hips become asymmetrical, the injured hip becoming shallower in a similar fashion.

Many will find that a very controversial statement. Dr. Corley from the OFA would reply to observations such as this, that he could prove that unilateral hip dysplasia was genetic, since it was almost always the left hip which was shallower. My response to his statement was that this proves to me that most dogs are right handed. The left diagonal being the master limb, the one with which the dog pushes off most strongly, and the one which is most liable to injury, especially stifle injury.

The conclusion from these observations is that the single most important environmental factor in a puppy's life is exercise, continuous and strenuous. Since this is often impossible for owners to arrange, the next considerations are to drastically restrict the diet of the growing puppy and to avoid strenuous exercise which will exhaust his muscles and leave him unable to protect his joints from injury. The puppy should be given frequent moderate exercise instead. This requires a different kind of time commitment from the owner.