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Hip Dysplasia |
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Definition Hip Dysplasia, otherwise known as coxo-femoral dysplasia, is defined by the International Dog Federation as a “disease affecting the development of the hip and causing instability in that joint”. In practice this means a poor juxtaposition of surfaces of the joint. The hip is a joint between a particular area of the pelvis known as the acetabulum, which forms a cavity, and the head of the femur. If the juxtaposition is a poor one, the head of the femur does not penetrate the acetabulum sufficiently and the acetabulum does not cover the head of the femur adequately. This disease affects many breeds, and the German Shepherd in particular, A not insignificant percentage of dogs seem to suffer from this disease according to the statistics drawn up by the international dog associations (the IDF, the Orthopedic Foundation for Animals, etc.) However the percentage of individuals affected varies depending on the specific type of animal, and the aesthetic types are more affected than the so-called working animal categories.
Symptoms. The disease can be presented in two ways depending on whether a puppy is still growing or has reached adulthood. The signs may appear in the first few weeks of life. A growing dog less that one year old will present irregularities when standing and when walking or running. When standing the rear limbs are positioned slightly backwards, and the ankles are drawn together, in order to minimize pressure at the hip. The sitting position is frequently asymmetrical, with one limb stretched out ,the other folded beneath the animals body, giving the impression that the dog is “sitting on its leg” Initially one is most aware of a so-called rolling gait, with the lower legs drawn close together, with simultaneous movement of the rear limbs when running, characteristic of the way rabbits hop. These symptoms have more to do with the instability of the joint than with a sensation of pain. Pain does not occur until some time after the first symptoms are present. It frequently takes the form of intense attacks with short episodes of acute limping. Functional deficit is then at its most significant, the animal being reluctant to stand up, to walk , to run, to climb stairs or to jump. The pain is associated with the phenomena of inflammation in the joint fluid, micro fractures, stretching of the ligaments and of the joint cavity. Frequently, after painful episodes during the growth cycle, there follows a clinically quite phase without any significant clinical symptoms, apart from a more noticeable tendency to tire. This quiet period may last some months to several years. The adult may then exhibit locomotor symptoms. The animal will be intolerant to exercise, preferring to sit and will find it difficult to stand up., accompanied by a certain degree of stiffness, particularly following a long period of inactivity, such as in the morning. Unilateral or even bilateral limping can occur, particularly after intense or prolonged exercise. These clinical symptoms are in this instance related to the development of osteoarthritis of the hip. There is no correlation between attacks of osteoarthritis and instability of the joint. Moreover attacks may occur at varying intervals and may be of varying degrees of intensity. Amyotrophy occurs following stiffness and painful movement. These different phases of the disease show why the diagnosis of dysplasia can be made in young dogs presenting the relevant symptoms or it may occur in adult dogs not presenting any abnormality in terms of their gait. Diagnosis The aim is to reach a diagnosis as early as possible. Palpation test are carried out first of all. In all cases these consist of moving the femur so as to slightly dislocate the joint. If it is possible right away to slightly remove the head of the femur from the socket and then to replace it, the animal may be considered as dysplastic. The various tests, known as the Barlow test, the Ortolani test and the Barden test, can be carried out by vets early. However it is not possible to deduce from a negative test that an animal is free from dysplasia; the tests serve only to detect a small number of affected dogs. X-Ray diagnosis is the most frequently used form. This examination is always carried out under general anaesthetic. (Note by the Webmaster: in most cases this is no longer required). The most common position is that by the American, Australian and European institutions (the OFA, the IDF, etc). The animal is placed on its back with the two femurs parallel. Their positioning is then assessed by examining the position and shape of the femoral head, the appearance and space between the femur and the pelvis, and the possible presence of osteoarthritic reshaping. It is also possible to calculate the angle between the line passing through the centre of the femoral heads and a right-angle connecting this centre and the edge of the acetabulum on the corresponding side. This angle is called the Norberg-Olsson angle. This technique can be used very early in the German Shepherds. However it is advisable not to employ it until the end of the first year. Another method is that developed at Pennsylvania University by Professor Smith: Pennsylvania Hip Improvement Program or PennHipMethod. However this method is patented and requires special training. The animal is placed on its back, an adjustable “distraction” system is securely applied to the pelvis and this makes it possible to slightly spread the limbs. This system makes it possible to calculate a distraction index or specific laxity fro the breed, which indicates the degree of stability at the joint. A similar method is used at the Zurich University in Germany. These methods seem more sensitive than the conventional technique. They also provide an earlier diagnosis, because the technique can be used at the age of four months. However, their cost and the limited number of people able to carry out the tests, has a limiting effect on their actual use. Other methods such as echography, scintigraphy, Magnetic Resonance Imaging, analysis of the joint fluid or even genetic analysis are still being developed and require further research before they can be considered reliable.
The treatment of hip dysplasia is complex problem which raises a number of issues. Treatment depends on the point at which intervention occurs. In the young dog is possible to perform surgical forms of treatment. The intervention takes the form of osteotomy (surgical section of the bone) on the pelvis and/or femur with the aim of re-establishing a good connection the joint. It is also possible to operate on the pubic symphysis in order to modify the animal’s growth and the development of the hip. In the adult dog the choice of treatment is more limited. For a dysplastic dog presenting osteoarthritic reshaping the bone it is possible to carry out a resection on the femoral head. The neck and head of the femur are thus removed and the painful contact points are suppressed. The joint itself no longer exists and the bones are held in position by the bundle of muscles. Another possible solution is to replace the natural structures with a prosthetic hip which gives the animal back a normal joint. However, for a dysplasic dog whose hips have undergone considerable alteration due to osteoarthritic reshaping, it is difficult to resort to surgery. Treatment must then be palliative, based on the use of analgesic and anti-inflammatory drugs. In all cases Hygienic measures are recommended. It is important not to allow the dog to become overweight, to limit exercise and to opt for long walks rather than brief periods of strenuous activity. Furthermore, in all cases treatment will be palliative, because a dysplasic animal will always be dysplasic. Genetic aspects Hip dysplasia is a hereditary disease, that is to say it is transmitted from one individual to its descendants in the genes. The exact method of transmission is still not known, though it is a transmission method which affects a number of genes (probably over 15). The term used is a “threshold” polygenic system, which means that an individual animal may be the carrier of coding genes fro dysplasia without exhibiting that disease because the number of genes is below the “threshold”. Moreover, the appearance of the hip is a phenotype in the dog. This actually represents the sum of the genotype (the information contained in the genes) and of environment effects (such as health, physical, human and nutrional factors). Thus the fact that a dog is free from dysplasia (phenotype) does not mean that it does not carry the genes (genotype).In other words there are “healthy carries” and these are difficult to detect. We use the term inheritability to define the proportion of a factor that is caused by genes. This is a figure that varies between zero and one. If inheritability is zero, the characteristic is not hereditary; if inheritability is one, the characteristic is determined wholly by genetics, and the environment has no effect at all. For hip dysplasia in the German shepherd the inheritability rating is often put at 0.40, which means that environmental factors have 60% effect on the emergence of the disease. Among these factors we first of all distinguish the rate of growth: the higher the speed of growth, the greater the risk. Diet is an important factor: most overfed animals with a corresponding excess of weight have a higher risk of developing the disease, particularly if the excess weight is noticeable from an early age. With regard to diet, the addition of vitamin C seems to give good results. Moreover physical exercise should be limited in puppies susceptible to developing dysplasia. The immature skeleton is unable to cope with the significant stresses that could be brought to bear on the body during extended, intense exercise. However, these recommendations relate to dogs that are potentially carries of the genes responsible for dysplasia. There is no value in restricting the diet of animals not pre-disposed to the disease. It would thus seem essential to ascertain whether a given individual is predisposed to the disease. This requires monitoring the development of the animals, which will also make it possible to introduce plans for eradication of the condition. Plans for eradication Hip dysplasia is a particular hereditary problem. But the way it is passed on makes it difficult to eradicate it: it is difficult to distinguish between dogs that carry the genes, but whose environment has been sufficiently controlled to reduce the visible expression of the disease, from “healthy carriers” who carry part of the genes, and the individuals that are completely free from it. Thus for many years different German shepherd clubs have been attempting to introduce programmes for its eradication. It is necessary first of all to avoid breeding from affected dogs.
However, only the more dysplasic grade is used to classify the animal itself. Thus if a dog has a class A hip and a class C hip, it will be regarded as class C. Using this classification system it makes sense to reject individuals that are too dysplasic (D and E) for reproduction purposes. This is a simple system, but it seems too imprecise because it fails to take account of the development of the individuals, so it would be useful if new X-rays were taken at the age of 24 months. Because of the complex way the disease is transmitted, this programme is slow and particularly effective. However it has the advantage of not eliminating too many dogs that are of value for characteristics other than the absence of dysplasia. The system developed by the German Shepherd breed club in breed club in many (SV) is worth noting. Here not only is the dog to be used for reproduction purposes examined, but its ascendants, siblings and cousins and nay descendants it has already produced are also taken into account. The same type of system has already been used for stock species. Thus each animal is given a number (known as Breed Value or Zuchtwert). This number can be calculated for each genetic characteristic. It measures the capacity for passing on the disease to its descendants. The figure 100 to average transmission. A dog whose value is above 100 will have less chance. Thus for undesirable conditions such as dysplasia, individuals whose Breed value is under 100 will be sought out. Moreover, the other significant change compared with the conventional method is that no animal is automatically removed from reproduction: this method operates on the basis of the “strategic mating” principle. In order that the litter can be registered with the Breed club it is necessary that the average of the Breed values of the two parents be 100 or less. Thus a stud which has very interesting characteristics, but which is very dysplasic, and whose BV is say 11, will not be automatically eliminated for reproduction purposes, but he may only be mated with bitches whose Breed Value is 85 or less. Calculation of the Breed Value is based on a number of criteria. Firstly the ascendants are studied: the value of the individuals is calculated initially on the basis of the average of the values for the parents, and the values relating to any litters already produced by the same two parents will be taken into account. After this the individual dog itself and related dogs will be examined: at the age of one year the dog’s hips are examined by X-ray, and the assessment of dogs from the same litter may also affect the Value. Finally any descendants will be examined: based on an assessment of the dogs produced by the individual in question its Breed Value will be re-assessed. At this stage it is sometimes difficult to distinguish what in the puppies produced relates more to the father or to the mother. The method for calculating the Breed Value is thus dynamic, evolving system which makes it possible not only to determine whether or not a characteristic is present, but above all to ascertain the extent to which it is transmitted. This is not a genetic assessment method, but a cynotechnic indicator for identifying dogs that are significantly predisposed to transmitting the disease. The drawback that is likely to become apparent is that the system is always based on conventional X-ray examination and on an ABCDE classification, which entails the areas of imprecision referred to above. However, this is the most common system used and the most widespread geographically. The adoption of a new procedure based on the Penn HIP technique would mean starting all over again, since it would be impossible to re-assess all the animals studied over the last ten years.
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( with permission copied from the Royal Canin Encyclopaedia/Aniwa publishing) |
Clinical
aspects.
Treatment
The most commonly
used procedure is that by the IDG and the OFA. The dog’s hips are X-rayed
at the age of 12 months. The X-rays may only be interpreted by an
officially recognized expert on the German Shepherd breed. Depending on
the classic criteria for assessment (the correct juxtaposition of the
bones, the appearance of the bones and joint, the presence or absence of
osteoarthritis), the joint will be graded in one of 5 classes from A
(free) to E (very dysplasic). For each dog both hips are examined and
graded.