Introduction
Hip dysplasia is a common, painful degenerative disease in dogs which causes arthritis-like symptoms and general hind end lameness. It is caused by a combination of genetic and environmental factors that lead to laxity (looseness) in one or both hip joints. Diagnosing this disorder can be difficult because a number of other diseases cause similar clinical signs and therefore must be ruled out before a definitive diagnosis of hip dysplasia can be made.
Diagnosing Hip Dysplasia
If a dog presents with unilateral or bilateral hind end lameness – especially if it is a young, rapidly-growing large or giant breed puppy between 4 and 12 months of age – the initial veterinary database normally will include blood work (complete blood count and serum chemistry panel run on fresh blood samples), a urinalysis, palpation of the hip joints (which may require sedation or even general anesthesia because of pain) and pelvic radiographs (x-rays). Very specific positioning of the dog for hip radiographs is essential to an accurate diagnosis of hip dysplasia and can be determinative even if the dog is not showing clinical signs of the disease.
Responsible breeders often have their dogs tested for hip dysplasia radiographically before breeding them. There currently are two procedures for this screening. The older and still more common method is recommended by the Orthopedic Foundation for Animals (the OFA). The dog’s veterinarian will take radiographs of the hips with the dog in a particular position – on its back, with its hind legs being stretched and slightly rotated – and will submit those films to the OFA. There, specialized veterinary radiologists will analyze the radiographs and compare them to a large computerized database of hip x-rays of other dogs to determine whether hip laxity exists and, if it does, how severe it is at that point. While this can be done in young dogs, official certification by the OFA (excellent, good, fair, borderline or dysplastic) must be done on radiographs taken after the dog is 2 years of age.
The other recognized method, called PennHip, was devised by doctors at the University of Pennsylvania. The radiographs for this method are taken at several specific angles and require the joint to be at its most relaxed, so general anesthesia normally is necessary. A mathematical formula is applied to the angles of bones evident on the radiographs to quantitate the degree of laxity in each hip joint. This formula yields a number which represents whether or not hip dysplasia is present.
Confirmatory testing might include additional x-rays taken at different views, and possibly computed tomography (CT or CAT scan).