While it is more difficult to manage disorders with this level of heritability, many traits in this range improve with proper selection. This means that 28 to 40 percent of the variation between affected and unaffected relatives is due to genes. Hip dysplasia is considered a moderately inherited disorder, with researchers computing heritability values of 28 to 40 percent. By computing a breed average of distractibility, and selecting for tighter hips than the breed average, it is believed that the incidence of hip dysplasia should decrease over time. PennHIP was designed to create a selection tool for tighter hips. Dogs with a DI of under 0.3 almost always have normal hips, and those over 0.7 are almost always dysplastic. A DI of zero indicates no laxity of the hips, and a DI of 1.0 indicates luxation of the hips. (Distractability is the distance that the soft tissue allows the head of the femur to come out of the acetabulum.) The measured difference between the compressed and distracted views is used to compute a distraction index (DI). The distracted-view radiograph (to the right) is taken while applying a uniform force on the hips to measure the maximum distractibility of the hip joints. This method utilizes two separate radiographs on an anesthetized dog to record the hips in compressed and distracted views.
The Pennsylvania Hip Improvement Program (PennHIP) method of evaluating the hip joint is based on laxity alone. A perfect rating would be zero the worst would be 106 (53 for each hip). The nine scores are added up for each hip, then totaled for the dog’s final rating. Unlike OFA’s rating system, it separately scores the nine anatomical aspects of the pelvic radiograph for each hip. The British Veterinary Association/Kennel Club (BVA/KC) evaluates the same extended-leg radiograph at 1 year of age or older. OFA will certify a dog’s hips (at 2 years of age or older) as excellent, good, fair, or borderline, or as mildly, moderately or severely dysplastic. Bony remodeling and arthritic changes will fill in the notch at the femoral neck, and cause “lipping” – proliferation of bone at the cranial acetabular rim. Good hip conformation is determined by imagining a line (dashed line in the drawing) connecting the outer edges of the acetabulum, and observing at least half of the femoral head enclosed within the acetabulum. These include a round femoral head, a deep acetabulum, a prominent notch in the femoral neck, a straight up-and-down cranial rim of the acetabulum, and minimal joint laxity. The OFA evaluates the hip radiograph for nine anatomical aspects. The hip is a ball (femoral head) and socket (acetabulum) joint. This hip-evaluation method is the one used by the Orthopedic Foundation for Animals (OFA), as well as by most European and Canadian dysplasia-control programs. This is a radiograph of the pelvis and hip joints taken with the dog on its back, with hind legs extended. The standard procedure is the extended-leg (x-ray). There are several methods used to diagnose hip dysplasia. Initial symptoms may appear from 4 months to 1 year of age, and include joint pain, a swaying and unsteady gait, “bunny hopping”, difficulty rising from a sitting position, difficulty with stair-climbing, and an aggravation of these signs with exercise. Most experts agree that the majority of dogs that develop hip dysplasia have outwardly normal hips when they are very young, and develop the anatomical or laxity changes associated with the disorder during the first year or two of life. The Pug, for example, has a significant frequency of affected dogs, while the Siberian Husky has a relatively low frequency of dysplasia. While hip dysplasia is commonly perceived to be a disorder of larger dogs, it also occurs in small breeds, mixed-breed dogs, and even cats. The disorder can include several abnormalities of the hip joints, such as joint laxity, anatomical abnormalities, and a predisposition to arthritis. It has been one of the fancy’s great challenges to combat and treat this hereditary developmental disorder, whose signs can include hip-joint pain, hind-limb weakness, lameness, exercise intolerance, degenerative joint disease, and arthritis. First printed in the July 2002 issue of the AKC Gazetteįor affected dogs, hip dysplasia can be a debilitating and painful disease.