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1. Hip Dysplasia

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During the last fifty years few things have proved such a difficult challenge to veterinary science as hip dysplasia. In this article we attempt to make the subject more accessible to the average dog-owner.

The hip joint is the point at which the rear limbs are connected to the pelvis. The head of the femur (thighbone) fits into the acetabulum, a hemispherical cavity in the pelvis. These two elements are connected by a round ligament and enveloped by an articular capsule. Dysplasia is the main hip disease in dogs and the most frequent cause of osteoarthritis in this joint. It is characterized by different degrees of looseness in the joint, which can lead to sublaxation (a pathological state in which the articular surfaces of a joint only partially connect with each other). As the condition worsens, deformity occurs in the structure of both the acetabulum and the head of the femur, which is accompanied by the development of degenerative joint disease. According to the Hip Dysplasia Registry of the Orthopedic Foundation for Animals, there are nine grades of congruity and fit between the acetabulum and the femoral head, the first three of which are considered to be normal states.
1. Excellent conformation
2. Normal conformation for age and breed
3. Less than ideal, but within normal radiographic limits
4. Near normal; minor hip joint abnormalities
5. Borderline; minimal dysplastic change
6. Grade 1 dysplasia: subluxated 25% 
7. Grade 2 dysplasia: subluxated 50%
8. Grade 3 dysplasia: subluxated 75%
9. Grade 4 dysplasia: dislocation of femoral head

Hip dysplasia is a hereditary disease, i.e. it is transmitted from parents to their offspring. Today, however, it is a well-known fact that other factors are also involved in the aetiopathogeny of the disease, such as a rapid rate of development in puppies (mainly of breeds with a large or massive build) and excessive exercise. The most crucial period is the first 60 days of the animal’s life. During this time both the muscles and the nerves connected with the joint are ‘immature’ and are of limited functionality. The tissues around the joint are soft and elastic, with the result that there is an ‘elastic limit’, a point beyond which the tissues do not return to their original state. It is very important, then, not to seek high rates of development in puppies (especially those belonging to breeds with large builds), nor to exercise them too much. This will reduce ‘stress’ on the joints and also the chances of the puppy suffering dysplasia.
Dysplasia affects all breeds of dog, though mainly, as was mentioned earlier, breeds with large builds. Although breeds with small builds may be affected, they do not display clinical symptoms. The latter depend on how loose the joint is, the existence of degenerative joint disease and the chronicity of the disease. The initial clinical symptoms are associated with the looseness of the joint, while those that appear later are associated with degenerative joint disease. 
The pain, which is the main clinical symptom, is due to minute fractures in the head of the femur in young animals and the existence of degenerative joint disease in older animals. The symptoms mentioned by owners are as follows: reduced mobility; difficulty in standing up from a sitting position; refusal to run, jump over obstacles or climb steps; an occasional or permanent limp in the rear limbs (which is often aggravated by exercise); a ‘rabbit-like’ hop (i.e. use of both rear limbs at the same time), a swaggering gait in the rear limbs; and a reduction in the amount of time the animal can spend resting on its hind legs. 
Diagnosis of the disease is based on clinical symptoms and even more on radiographic examination, which may serve to confirm it. Treatment of dysplasia of the hip joint depends on how big, old and active the dog is, how loose the joint is and whether degenerative changes have occurred or not. The dog’s activity should be restricted in order to reduce the inflammatory reaction in the articular capsule.
Physiotherapy (passive movements of the joint) and swimming help considerably, for they help to keep the joint and the surrounding muscles mobile without the joint itself having to bear the weight of the body. It is also important to maintain the animal’s body weight within the normal limits for its age and breed. Non-surgical treatment is carried out in the cases of animals that are only mildly affected or those which have just begun to display bouts of limping. Usually analgesic and anti-inflammatory drugs are administered, which reduce the pain.
As far as surgical treatment is concerned, there are certain types of intervention whose purpose is simply to relieve the pain and others that aim partly to repair the structure of the joint. The choice of surgical intervention is always based on the exact condition of the particular animal concerned (age, body weight, existence of degenerative joint disease). A few examples of these interventions are: excision of the pectineus muscle, excision of the head and neck of the femur, triple pelvic osteotomy, and total replacement of the joint. 
Finally, I should like to stress something that every dog-owner ought to know: dysplasia of the hip joint is a HEREDITARY disease! It is imperative that all animals that are not in a normal condition SHOULD BE EXCLUDED from breeding purposes. This is the best form of ‘treatment’ for dysplasia.

CORRECT POSITIONING IN RADIOGRAPHIC EXAMINATION FOR DIAGNOSIS OF HIP DYSPLASIA

By the veterinary surgeon Spyros Tachos
Hip dysplasia is a common disease which appears mainly in large breeds of dogs. As was pointed out in the previous article, it is in effect an anomaly in the hip joint, in which mainly hereditary and, to a lesser degree, environmental factors play a role. As far as the aetiology, symptomatology, diagnosis and treatment of the disease is concerned, extensive reference was made in the previous article. This article aims to deal in greater depth with its diagnosis, which is based on a radiographic examination of the animal suspected of having the disease.

In the radiographic examination of animals suspected of suffering from hip dysplasia a very important role is played by the correct positioning of the animal at the moment the X-ray is taken. Various radiographic techniques have been proposed from time to time, but since 1961 the technique that has gained universal acceptance is that known as the ventro-dorsal view. In this technique, the animal should be held down in a supine position (i.e. on its back), with its hind legs stretched out backwards so that the joints of the hips, knees and hocks are fully extended. In addition, the femurs should also be exactly parallel to each other and at the same time parallel to the spinal column, the table on which the dog is lying and the borders of the X-ray image. Also the thighs should be turned slightly inwards (i.e. towards each other) in order to bring the patellas into a central position. The pelvis should not be turned in any direction. In order to hold and keep the animal still in this position usually a sedative is required, or even a general anaesthetic. The X-ray should take in the whole of the pelvis and the femurs up as far as the patellas. Holding the dog in the wrong position will produce X-rays that either cannot be properly evaluated or, if evaluated, may lead to erroneous conclusions. 
There are certain points in the X-rays that can be easily checked, even by the dog-owners themselves. 
These are shown in Fig. 1 and are as follows:

a) The holes in the bone structure should be symmetrical (yellow arrows);
b) The wings of the iliac bones should be symmetrical (green arrows);
c) The femurs should be parallel to the spinal column;
d) The sections of the ischial bones that are covered by the femurs should be symmetrical (red arrows);
e) The pelvic cavity should look circular (and not oval-shaped) and the parts of it that protrude on either side of the spinal column should be symmetrical (blue arrows).
If an X-ray does not satisfy the above requirements, or at least most of them, it cannot produce a definite diagnosis. In such cases the X-ray should be taken again. The importance of holding the animal in the correct position while taking the X-ray can be seen very clearly in the following X-rays, which are of the same dog and were taken on the same day. In the first X-ray (Fig. 2) the position of the dog is correct (though not 100%), while in the second one (Fig. 3), because the pelvis has been turned, it looks oval in shape, with the parts of it that are visible on either side of the spinal column appearing quite asymmetrical: Also, the gap between the left femur and the hip socket is wider than that between the socket and the right femur (Fig. 4, green arrows), which creates the impression that the head of the left femur is not lying completely within the acetabular cavity (Fig. 4, red arrow) and that the dog is suffering from dysplasia. In this case, an evaluation of the X-ray in Fig. 3 will lead to the conclusion that the dog is dysplastic while in fact it is not, as can be seen from the X-ray in Fig. 2, which was taken with the dog placed in a more correct position. This shows the great importance of correct positioning in testing for the presence of hip dysplasia. It should be noted, however, that there are cases of animals with severe hip dysplasia in which the degenerative changes are so obvious that their position at the time the X-ray is taken does. not seriously affect the final diagnosis. In addition, it should also be clearly understood that the radiographic image does not always correspond to the animal’s clinical condition, and so animals displaying radiographic evidence of dysplasia may appear clinically healthy and free of pain or difficulty in moving their hind legs. 
In spite of all this, however, in each case an attempt should be made to take an X-ray with the dog in as correct a position as possible. This is particularly important in the case of young animals, as very often the result of this examination will determine their reproductive future.

The previous article referred to the correct positioning of animals during radiographic examination for hip dysplasia. This article will deal with the radiographic findings, which are evaluated in order to form a diagnosis of hip dysplasia and to assess its severity. 
First of all, there should be a clear understanding of the anatomical structure of the acetabulum in relation to the head of the femur (thighbone). This is illustrated in Fig. 1.
The parameters that are assessed in order to diagnose the presence of dysplasia and to gauge its severity are the following:

1. The Norberg angle: the angle formed by a line drawn between the centres of the femoral heads and a second line drawn from the femoral head to the cranial edge of the acetabulum on each side ((Fig. 2).
2. In normal joints the Norberg angle should be greater than 105o.
3. The width of the cranial joint space and the distance between the centre of the femoral head and the dorsal acetabular edge, which in normal joints should be greater than 2 mm (Fig. 3).
4. The cranial acetabular edge (the front outer edge of the acetabulum), which in normal animals should be parallel with the femoral head
(Fig. 4).
5. The cranial subchondral acetabular bone, which in normal joints should be smooth (Fig. 5).
6. The morphology of the femoral head and neck: in normal animals the head should be spherical and the neck well demarcated (i.e. distinguishable from the head and thinner than it).
7. The Morgan line, which is visible in animals with dysplasia and is created by the presence of osteophytes on the neck
(Fig. 5).

Each of the above parameters is evaluated on a scale of 0 to 5, together with the radiographic findings (Table A). Once all of the parameters have been evaluated and given a score for each joint, the scores are added up, giving a total score for each joint. On the basis of this overall score the degree of dysplasia in each joint is assessed (Table B).
It should be noted that because the parameters mentioned in Table A include terms like ‘slightly’, ‘minor’ and ‘considerable’ which it is difficult for all examiners to interpret in the same way, slight deviations in scoring are justified when the scores are produced by different examiners.