Malformation of the hip joint is a common abnormality in large and giant-breed dogs. Hip dysplasia, as this condition is called, causes joint instability that leads to inflammation, subsequent arthritis and crippling pain.
Prevalence

According to the Orthopedic Foundation for Animals (OFA), hip dysplasia (HD) affects between 10 and 50 per cent of the popular breeds. Researchers at the University of Pennsylvania believe prevalence figures are actually two to three times higher than those published by the OFA because only hip radiographs with the greatest likelihood of grading normal are submitted for assessment. However, the exact incidence doesn’t matter. HD is a huge problem to owners and breeders.

The development of HD is influenced by both genetic and non-genetic factors. Many breeders try to produce puppies free of HD by mating only dogs deemed clear of the disease. They evaluate hips by using one of two screening programs. Most breeders rely on OFA certification, for which the dog’s hips are radiographed in a fully extended position. The radiographs are submitted to veterinary radiologists, who grade the degree of HD or deem the hips free of disease.

The second way to assess hips is to use the PennHIP program. Specially trained veterinarians take radiographs of hips that are “distracted” (levered from the joint). The amount of distraction is then quantified to determine if HD is present, and its significance.

Though these tests indicate if a specific dog is clear of HD, they don’t guarantee that the dog’s offspring will be free of disease. HD does occur from “clear” breedings. Obviously, there is more to it than basic heredity.

Non-genetic factors that impact the appearance of HD the most are growth rate and weight. In a 14-year study done by Purina, dogs prone to HD were fed all they wanted (control group) or 75 per cent of what the control group ate (restricted group). The two groups were easy to tell apart – they were either obese or lean.

By five years of age, 52 per cent of the control dogs showed signs of arthritis in their hips while only 13 per cent of the restricted group were affected. A dog genetically set up for HD may not develop clinical disease if kept lean.

Does exercise have a bearing on HD? Excessive trauma to the hip joint is believed to stretch the ligament that holds the hip in place, increasing the likelihood of clinical HD. On the other hand, exercise keeps muscles toned, which helps protect the hip joint. The logical approach is to provide dogs with adequate exercise to tone their muscles, but not uncontrolled activity, which may stress the joint.