Introduction

Hip dysplasia is a painful degenerative disease in domestic dogs which causes arthritis-like symptoms and general hind-end lameness. It is caused by a combination of genetic, environmental and nutritional factors that contribute to laxity in one or both hip joints. Diagnosing this disorder is not particularly difficult, although a number of other diseases cause similar clinical signs and must be ruled out before a definitive diagnosis of hip dysplasia can be made.

How Hip Dysplasia is Diagnosed

When a dog presents with unilateral or bilateral rear-end lameness – especially if it is a young, rapidly-growing large or giant breed puppy under 12 months of age or an aging adult – the initial veterinary database normally will include a thorough history and physical examination, followed by blood work (complete blood count and serum chemistry panel run on fresh blood samples), a urinalysis and manual palpation of the hip joints (which may require sedation or even general anesthesia because of pain). The best way to definitively diagnose hip dysplasia is through properly taken pelvic radiographs (x-rays). Very specific positioning of the dog for hip radiographs is essential to an accurate diagnosis of hip dysplasia. Radiographs can be diagnostic even in dogs not yet showing any symptoms of the disorder.

Many reputable breeders have their dogs screened 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 recommended by the Orthopedic Foundation for Animals (OFA). A veterinarian will take radiographs of the hips with the dog in a very specific position – on its back, with its hind legs pulled back, stretched and slightly rotated inward – 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. The films of dogs with hip dysplasia will show a shallow acetabulum (the concave socket in the pelvis into which the ball of the long femur (thigh) bone sits), a small misshapen femoral head and sometimes small bony outgrowths called osteophytes. While this procedure can be done in young dogs, official certification by the OFA (excellent, good, fair, borderline or dysplastic) must be done on radiographs taken after a dog is 2 years of age. Most veterinarians recommend taking OFA films with the dog under general anesthesia or heavy sedation. The positioning can be painful, and non-sedated dogs can tighten their hind-end muscles and “pull” their femurs into their hip joints, making them look tighter and more normal than they may really be.

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 either confirms or rules out hip dysplasia.

Special Notes

Confirmatory testing might include additional x-rays taken at different views and at different points in time, and possibly use of computed tomography (CT or CAT scan). However, advanced testing is almost never necessary, because traditional radiographs are almost always diagnostic of hip dysplasia.