Hip Dysplasia in People and Pups: A Demographic Comparison

In an article recently published in the Journal of Veterinary Medicine, researchers used data from the Orthopedic Foundation for Animals to analyze the demographics of canine hip dysplasia (CHD) in the United States and Canada. The authors also discussed the similarities between CHD and developmental dysplasia of the hip (DDH) in humans.

Studies have shown that demographic factors such as sex, race, latitude, and season of birth affect the incidence of DDH in humans. Although some analyses of CHD demographics have been published, none have been based on a large data set.

“Comparison with the demographics of DDH may shed further light on the etiology of both conditions and specifically support the use of CHD as an animal model for DDH, as well as DDH pointing towards further comparative research areas in CHD,” wrote the authors.

The investigators analyzed the records of 921,046 dogs from the United States and Canada collected in the hip dysplasia registry of the Orthopedic Foundation for Animals. Because the data set contains voluntarily submitted records, it may be subject to selection bias, the investigators acknowledged. They examined CHD risk by individual breed and among breed groups recognized by the American Kennel Club (AKC) and the Fédération Cynologique Internationale (FCI).

The overall prevalence of hip dysplasia was 15.56%. Prevalence varied significantly by breed, ranging from 0% in the Italian greyhound to 77.7% in the bulldog. Among AKC groups, the risk of CHD was highest in the working dog group and lowest in the hound group. Among FCI groups, the risk was highest in the group comprising pinschers, schnauzers, Swiss mountain dogs, and molossoid breeds (bulldogs, bullmastiffs, Rottweilers, Newfoundlands, and others); it was lowest in sighthounds.

Hip dysplasia was slightly more common in dogs born in the winter and spring. The authors suggested that outdoor exercise (as opposed to indoor confinement), weight gain in winter months, and vitamin D levels could contribute to the seasonal differences.

A new finding of the study was that CHD was more common in southern latitudes. The authors speculated that this finding could be related to gene pools in different areas, diet, growth rate, or physical activity. Time spent with hips in abduction and flexion appears to reduce the risk of both CHD and DDH, they said, and dogs in warmer climates may have higher activity levels and thus spend less time with their hips abducted and flexed. They added that this finding requires further study.

In about one-third of dogs, CHD was unilateral. Bilateral CHD, which was more often associated with severe disease, was most common in terriers and least common in mixed-breed dogs (AKC classification) and sighthounds (FCI classification). CHD was slightly more common in female dogs, although this varied by breed.

The authors noted that the demographics of CHD are comparable to those of humans with the subtype of DDH that manifests as late-onset acetabular dysplasia (as opposed to infantile DDH). Similarities between CHD and human DDH include race- or breed-associated prevalence, female predilection (more substantial in humans than in dogs), and prevalence associated with season of birth. Unlike CHD, DDH in humans is more often unilateral and is more prevalent in northern latitudes.

“The similarities between CHD and DDH are striking, especially late-onset DDH, and suggest that comparative studies of both disorders should lead to a better understanding of a problem that leads to debilitating hip osteoarthritis in both canines and humans,” concluded the authors.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.