Hip dysplasia is a common degenerative disease that causes hind-end lameness and pain. It is probably caused by a combination of genetic, environmental and nutritional factors that contribute to hip joint laxity and deterioration. Diagnosing hip dysplasia is not particularly difficult, although a number of diseases cause similar signs and must be ruled out before a definitive diagnosis of dysplasia is made. When a dog is limping, painful and weak in one or both rear legs - especially if it is a young, rapidly-growing large or giant breed puppy or an older overweight adult – the initial veterinary evaluation will include a thorough history and physical examination, followed by routine blood work (complete blood count and serum chemistry panel run on fresh blood samples) and a urinalysis. The veterinarian will carefully palpate (feel) the dog’s hips and legs; this may require sedation or general anesthesia.
The only reliable way to diagnose hip dysplasia is by evaluating properly taken X-rays (radiographs) of the hips and pelvis. Properly positioned radiographs can be extremely useful even in dogs not showing any clinical signs. Many reputable breeders screen their dogs for hip dysplasia before using them in a breeding program. Currently, there are two recognized procedures for this screening. The older and still more common method is run by the Orthopedic Foundation for Animals (OFA). The dog’s veterinarian will take radiographs of its hips with the dog on its back and its hind legs parallel, extended and slightly rotated inward. Most authorities feel that good hip radiographs must be taken under heavy sedation or general anesthesia; otherwise, the pain of the procedure can cause the hip sockets to look tighter than they actually are and artificially improve the results. The pelvis must not be tilted. The images will be sent to OFA, where radiologists will compare them to a computerized database of other hip x-rays. They will determine whether abnormal hip laxity exists and, if so, how severe it is. Normal hips are rated excellent, good or fair; dysplastic hips are rated mild, moderate or severe. If the images aren’t clear, the dog may receive a borderline rating. Although preliminary OFA screening can be done in young dogs, official certification is only available after a dog turns 2 years of age.
The other recognized screening method, PennHip, was devised by doctors at the University of Pennsylvania Veterinary School. PennHip radiographs are taken at very precise angles; they require the hip joint to be at its most relaxed, making general anesthesia normally necessary. PennHip evaluation can be done on puppies as young as 16 weeks old. A mathematical formula is applied to the angles of bones in the hip joint to quantify the degree of laxity in each joint, which is then compared with other dogs of the same breed. This formula yields a number which either confirms or rules out hip dysplasia, ranging from 0.0 (perfect) to 1.1 (severely dysplastic).
Confirmatory testing might include x-rays taken from different views and at different times, and use of computed tomography (CT or CAT) scanning. However, advanced testing is almost never necessary, because traditional techniques almost always confirm or rule out hip dysplasia.