Hip dysplasia is a complex disease. It was first described in the 1930s and was thought to be a rare, uncommon affliction. The disease process begins early in life, and as it progresses, causes a deformation of the hip joint as well as the development of DJD (degenerative joint disease – commonly called arthritis). Abnormal hip joint laxity (looseness between the ball and socket portion of the joint) is the initiating factor that results in hip dysplasia.
Hip dysplasia can be seen in almost all breeds of dogs, although it occurs most commonly in large and giant breeds. It is the most common inherited joint disease of large dogs and the most important cause of arthritis in the hip. Breeds of dogs with a high incidence of hip dysplasia include Akitas, German Shepherds, Labrador Retrievers, Golden Retrievers, Rottweilers, Newfoundlands, and Chow Chows.
Hip dysplasia is not caused by one single genetic anomaly. It is a polygenetic, complex disease, caused by multiple genes. The expression of the disease, or how it affects individual animals, depends upon several factors. Altering the environment in which the puppy is raised can contribute to the severity of symptoms. Experiments have shown that low-protein diets and reduced activity during the puppy stage may reduce the symptoms of hip dysplasia. Even though symptoms may not be as severe in these dogs, they still have dysplastic hips and carry the genes that contribute to the disease. Another factor that influences the symptoms of hip dysplasia is pain-tolerance level. Like humans, individual dogs have different levels of pain tolerance. Some dogs with mild hip dysplasia have painful hips and are severely crippled. Other dogs with similar radiographic features do not have painful hips and do not exhibit the same degree of lameness. In both situations, the dogs have dysplastic hips and should not be considered for breeding.
Radiography (X-rays) is the only method for accurately diagnosing canine hip dysplasia. Presently, there are two radiographic techniques for evaluating canine hip dysplasia. Of the two methods, the PennHIP technique is more accurate than the current standard and it has been shown to be a better predictor for the onset of DJD (degenerative joint disease).
In 1983, Dr. Gail Smith, a veterinary researcher at the University of Pennsylvania School of Veterinary Medicine, conceived and developed a new scientific method for the early diagnosis of Canine Hip Dysplasia (CHD). This program, called PennHIP (University of Pennsylvania Hip Improvement Program), measures hip joint laxity and can accurately predict the onset of degenerative joint disease in dogs as young as 16 weeks of age. This is compared to the older less reliable technique that cannot be performed until the dog reaches two years of age.
The PennHIP method consists of three separate radiographs. The distraction view is used to obtain accurate and precise measurements of hip joint laxity. The compression view is used to obtain accurate and precise measurements of hip joint congruity. The hip-extended view is used to obtain supplementary information regarding the existence of degenerative joint disease in the hip joint.
Hip laxity was shown to be the primary risk-factor predicting the development of degenerative joint disease. Specifically, the looser the hip joint, according to the PennHIP method, the greater the chance that the joint would develop DJD. Passive hip laxity at 16 weeks correlates highly with later hip laxity. In other words, a dog’s hip laxity at 16 weeks would be much the same at one year, two years or even three years.
To obtain diagnostic-quality radiographs, the musculature around the hip joint must be completely relaxed. For the comfort and safety of the animal, this requires either heavy sedation or general anesthesia. The type of sedation / anesthesia is determined by the veterinarian performing the PennHIP procedure. After the radiographs are performed and developed, they are submitted to PennHIP for evaluation. The owner and the participating PennHIP veterinarian receive the dog’s Hip Evaluation Report in the mail. This report contains the patient’s distraction index (DI), which is the measure of passive hip laxity. The report also contains the dog’s Hip Laxity Profile and the percentile group for his or her individual breed. Though somewhat involved, the report gives the pet owner and veterinarian information to accurately predict susceptibility to developing DJD on dogs as young as sixteen weeks of age.
Here at Society Hill Veterinary Hospital, Dr. Casavecchia is certified to perform the PennHIP procedure.