Canine Hip Dysplasia - Diagnosis
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| Definition | Risk Factors | Effects |
| Symptoms | Diagnosis | Prevention |
Hip Dysplasia Diagnosis
Diagnosis of hip dysplasia in dogs is usually made by a veterinarian through a combination of a physical exam and X-rays. The veterinarian may even be able to feel looseness in the joint or may be able to elicit pain through extension and flexion. Regardless, the results are straightforward and usually not difficult to interpret.
However, about half of the animals that come in for a determination on the health of their hip joints are not showing physical signs, but are intended to be bred. The breeder wants to ensure that the animal is not at great risk for transmitting the disease to his or her offspring.
Hip Dysplasia Testing Methods
There are two different testing methods that can be performed: the older OFA testing and the newer Penn HIP method.
OFA: The method used by the Orthopedic Foundation for Animals (OFA) has been the standard for many years. The OFA maintains a database of hip evaluations for almost half a million dogs. Radiographs are taken by a local veterinarian under specific guidelines and are then submitted to the OFA for evaluation of hip dysplasia and certification of hip status. Since the accuracy of a dog’s diagnosis of hip dysplasia using the OFA technique increases after 24 months of age, the OFA requires that the dog be at least two years of age at the time the radiographs are taken. They also recommend that the evaluation not be performed while the female is in heat. To get the correct presentation and ensure that the muscles are relaxed, the OFA recommends that the dog be anesthetized for the radiographs. OFA radiologists evaluate the hip joints for congruity, subluxation, the condition of the acetabular margins, and acetabular notch, and the size, shape, and architecture of the femoral head and neck. The radiographs are reviewed by three radiologists and a consensus score is assigned based on the animal's hip conformation relative to other individuals of the same breed and age. Using a seven-point scoring system, hips are scored as normal (excellent, good, fair), borderline dysplastic, or dysplastic (mild, moderate, severe).
PennHIP: The diagnostic method used by the University of Pennsylvania Hip Improvement Program (PennHIP) uses distraction/compression radiographic views to more accurately identify joint laxity. Radiographs of the hip joints are taken with the dog under heavy sedation. Two views are obtained with the hind limbs in neutral position; this maximizes joint laxity. Weights and/or other devices are used to help push the head of the femur further into or away from the acetabulum. The amount of femoral head displacement (hip joint laxity) is quantified using a distraction index (DI). The DI ranges from 0 to 1. It is calculated by measuring the distance the center of the femoral head moves laterally from the center of the acetabulum and dividing it by the radius of the femoral head. A DI of 0 indicates a very tight joint. A DI of 1 indicates complete luxation with little or no coverage of the femoral head. A hip with a distraction index of .6 is 60% luxated and is twice as lax as a hip with a DI of .3. When the DI was compared to the OFA scores for 65 dogs, all dogs scored as mildly, moderately, or severely dysplasticby the OFA method and had a DI above .3.
Hip joint laxity as measured by the DI is strongly correlated with the future development of osteoarthritis. Hips with a low DI are less likely to develop osteoarthritis. Hips with a DI below .3 rarely develop osteoarthritis visible on radiographs. Although hips with a DI above .3 are considered "degenerative joint disease susceptible," not all hips with a DI greater than .3 eventually develop osteoarthritis. It is known that some hips with radiographically apparent laxity do not develop osteoarthritis. A means of differentiating lax hips that develop osteoarthritis from those that do not is important in developing a prognosis and making treatment recommendations. In one study, the DI obtained from dogs at four months of age was a good predictor of later osteoarthritis, though the 6- and 12-month indices were more accurate.
To assure quality and repeatability among diagnostic centers using PennHIP, veterinarians must take a special course and become certified. As this technique gains popularity, more veterinarians are becoming certified.
Anesthesia: During the diagnosis, anesthesia is necessary. To yield an X-ray with the information the owner is trying to discover, the dog must be perfectly relaxed. Because the position required to take a diagnostic X-ray is unnatural, even very gentle, cooperative dogs cannot relax enough to be X-rayed properly. It is frustrating for the veterinarian for an owner to claim that anesthesia is not necessary, that the dog will “do anything you tell it to.” Unless at the time of exposure of the X-ray the dog is positioned precisely, with no movement, the X-ray will not be credible.
Another great advantage of anesthesia is that it allows the veterinarian to palpate and manipulate the hips to actually feel the degree of looseness. Also, the tension of the Pectineus Muscle is best assessed under anesthesia. Any grating or grinding from calcium deposits along the hip joints can be evaluated better in a sleeping dog than in one that is awake. Let sleeping dogs lie, indeed. If the pelvis is tipped only slightly to one side or the other, one hip that isn’t normal can appear to be and one that is not dysplastic can appear to be. To complicate things, 10% of dysplastic dogs will be affected in only one hip. The X-ray should be done right.
X-rays can be done as early as at five or six months of age, if dysplasia is suspected. The advantage of radiography in a younger animal is that if you plan to breed it, you can save the time and financial and emotional expense related to breeding if the X-rays show unquestionable hip dysplasia. Again, the advantage of the PennHIP procedure is obvious, since dogs over four months of age can be evaluated.
It is very sad indeed for any pet owner to see his or her special pal affected by the discomfort and mobility problems associated with Canine Hip Dysplasia. Armed with knowledge and forethought, highly selective breeding is your best defense against CHD.
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