Hip Dysplasia is an inherited deformity of the hip structure. The acetabulum is a depression in the pelvic bone into which the head of the femur rests, forming a ball-and-socket joint. Ligaments attach the bone structures to the muscle mass. Proper hip movement depends on these structures working together. Hip dysplasia is the condition in which either the acetabulum is too shallow to adequately hold the femoral head in place or the femoral head does not fit properly into the acetabulum. Varying degrees of severity may be seen from mild, asymptomatic dogs to severely dysplastic dogs with complete dislocation of the hip joint. The degree to which the dog exhibits symptoms is influenced by many factors such as the strength of the muscle and ligament attachments which help to hold the joint in place. Other factors include rapid growth and weight increase which stresses the joint. Studies have proven that dysplastic puppies whose diet is controlled to slow growth and weight gain may exhibit no outward appearance of disease and remain functional despite severe dysplasia. This approach allows the muscles and ligaments to develop enough to compensate for the bony failings. However, this does not alter the dogs genetic ability to pass on the defect to its offspring.
The exact mode of inheritance has not been identified although it is certainly polygenic, or influenced by several genes and modifiers working in combination. Affected dogs bred to affected dogs produce dysplastic puppies with some consistency, and the more severely affected the parents are the more likely they are to produce affected offspring. However, unaffected dogs bred to unaffected dogs can also produce dysplasia. To avoid producing dysplastic dogs only those with above average hip conformation should be bred. Further, breeding should be withheld until evaluation has been done. There is no way to predict the soundness of the hip structure based on movement or palpation alone. Many dysplastic dogs have developed compensatory mechanisms that allow them to move well and remain active. Quality of movement does not accurately reflect the presence or absence of dysplasia. The x-ray has been proven to be the most accurate means of diagnosis.
The Orthopedic Foundation for Animals was formed in 1966 and has been instrumental in diagnosing and controlling the disease in the United States. Originally dogs were x-rayed at 12 months of age, however the accuracy of diagnosis was significantly improved when, in 1974, OFA increased the minimum age to 24 months. A single x-ray of the hip is taken by a veterinarian and sent to the Orthopedic Foundation. Once there, the films are read by a panel of three Veterinary Radiologists who evaluated the laxity or looseness of both hip joints. Hips are then rated "Excellent" (superior hip conformation), "Good" (well formed hip conformation) or "Fair" (minor irregularities) as compared to other dogs of the same age and breed. Currently, OFA reports a 95% accuracy rate in diagnosing hip dysplasia. Many breeders will have preliminary x-rays evaluated on their potential breeding dogs before a great deal of time and effort is invested in showing and campaigning the dog. This is not required, but can save a lot of grief later if the dog is found to be dysplastic. Preliminary x-ray evaluations are performed by OFA between 12 and 24 months; the accuracy however varies from 100% accurate when rated Excellent, 98% when rated Good and 77% accurate for Fair ratings. 90% of dogs who are found to be dysplastic prior to 24 months will be dysplastic in later evaluations. One must remember however that final diagnosis of the disease cannot be made until the joint is fully formed at maturity. This is because hip dysplasia, while unarguably genetic in predisposition is also affected by such environmental factors as nutrition and level of activity.
Other techniques have been developed over the years for identifying hip dysplasia in dogs in addition to the OFA method. The Laxity Distance Method was developed in 1977 to predict hip dysplasia in puppies 8-9 weeks old by palpating and manipulating the joint. To date, this method remains subject to the skills of the examiner and has a distressingly high rate of error when confirmed by radiography.
Then Penn-Hip method of radiography and hip evaluation was developed by researchers at the University of Pennsylvania in 1983 and offered as a service in 1993. Currently, Penn-Hip evaluation is controlled by Symbiotics Corp. as the database and ability to manage the program outgrew the University’s resources. Penn-Hip requires three x-rays with the hip in various positions. Each hips laxity or looseness is then measured mathematically. A "passing" measurement is based on the average for the breed. While more expensive, the advantages of the Penn-Hip evaluation are in it’s objectivity and accuracy at ages as young as 16 weeks.
Treatment options for dysplastic dogs varies based on the degree of dysplasia seen and severity of symptoms. Mild disease can often be managed with weight control, moderate exercise and drugs such as Rimadyl, Esogesic and/or chondroitin sulfate/glucosamine (Cosequin). If these therapies are unsuccessful your vet may suggest surgery to remove the femoral head (excision arthroplasty). Other surgical options include pelvic rotation to move the hip socket outward to provide more coverage for the head of the femur, or total hip replacement. Most dogs may lead a normal and moderately active life with these improved therapies and treatments.
Hip dysplasia incidence can be controlled. Reputable breeders should always have breeding dogs evaluated and puppy buyers should insist upon seeing the paperwork. By carefully screening out affected dogs from breeding, we can eliminate this heritable disease in the North American Miniature Australian Shepherd.
Statistics From The Orthopedic Foundation for Animals 1999 These are the combined figures for dogs evaluated as North American Miniature Australian Shepherds and Miniature Australian Shepherds.
Orthopedic Foundation For Animals:
Univ. of Pennsylvania Hip Improvement Program:
Genetic Disease Control