Hip dysplasia (HD)

The canine hip dysplasia (HD) is one of the most common musculoskeletal disorders that affects medium-sized to large dogs, both pedigree and mixed-breed dogs. For a few decades, veterinarians, scientists and breeding organizations have been dealing in detail with this disease. Today we know relatively exactly how the disease develops; the causes of the disease are also largely known. Even if there are sometimes different opinions about the triggering factors or their weighting, there is nowadays agreement that HD is largely hereditary and, due to its polygenic inheritance and its multifactorial expression, is influenced by some non-genetic factors.

Disease emergence

If there are genetically determined deviations in the form or interaction of the structures mentioned, such hip joints are referred to as dysplastic. Such a malformation or malformation of one or both hip joints can have different degrees of severity. The form of HD is also diverse. The acetabulum may be too flat and / or the femoral head too small. Any discrepancy in the correspondence of the cup and head is called an incongruence.
Some authors blame muscle anomalies (primarily a shortened pectineus muscle). As a result, the femoral head attached to this muscle is permanently pulled up against the socket wall, which in turn is supposed to lead to the known sequelae.
Another cause of HD is that the joint is too loose, ie the head is not seated firmly and tightly enough in the socket. Reasons for this are, for example, slack ligaments or joint capsules.
Both incongruence and too loose joint closure can lead to secondary degenerative changes over time. These appear sooner or later as a loss of the articular cartilage as well as exostoses and arthroses due to the permanent incorrect loading of the joint surfaces. As an extreme consequence of this, a dislocation of the hip joint can occur. The bony changes that are often found on the x-ray in advanced HD are not symptoms of the actual disease, but rather sequelae. This is known as coxarthrosis.

Causes of the appearance of HD

HD is a genetic condition. In contrast to certain body characteristics and also certain hereditary diseases (including metabolic diseases), not a single gene is responsible. Rather, the ability to develop HD is influenced by different genes; this type of inheritance is also called polygenetic (poly = a lot). This is also one of the reasons why there is no "all-or-nothing principle" with the HD, but all conceivable degrees of severity.
The involvement of various environmental factors also plays a role here. Particularly noteworthy are feeding and exercise. Lately, in particular, the opinion has been heard that HD is an exclusively environmental disease. However, it has been certain for some time that this is not the case. The only question is what part do genes play and what part do rearing and environmental conditions play. A factor of 50/50 is largely assumed today.

The occurrence of HD is different in the individual dog breeds, sometimes even the same breed has a different frequency in different countries. Primarily medium-sized to large breeds are affected.

As we now know, the dog inherits a certain predisposition to develop HD. He already has this disposition at birth. At this point in time, however, a diagnosis is not yet possible, as the features of dysplasia only develop in the course of skeletal development. In some cases, these features can already be identified at an age of a few weeks to months, but a clear and definitive diagnosis can only be made after growth has ended, i.e. from an age of 12 to 18 months. The above-mentioned environmental factors also affect the dog from birth. The type of feeding and the type and extent of exercise are of the greatest importance here. Feeding that is too high in energy or too high in protein has proven to be disadvantageous, especially for large-bred dogs. Excessive physical work, e.g. exercising too early and too long, especially on the steep face, has a negative effect on the development of the hip joints. Tight croup and thigh muscles through moderate, even movement, on the other hand, are beneficial for stabilizing the hips. Optimal rearing conditions, which should be a matter of course for conscientious breeders and owners anyway, are an absolute must for rearing HD-endangered breeds and dogs.

The clinical symptoms of HD range from reduced activity, which is of course particularly noticeable in young dogs, through pain when standing up to passive movement of the hip joint. The veterinarian can use a certain manipulation to provoke a snapping sound of the joint, which is also typical for HD. A reliable diagnosis, however, can only be made through x-rays.

diagnosis

X-rays are still the most important diagnostic tool. For some breeds, breeding approval is mandatory, in general every dog from medium size (including mixed breeds) should be x-rayed at a certain age (at least 12 months) in order to be able to determine incongruences or deformed joint parts.

The dog is sedated for correct HD recording. This is necessary in order to achieve complete relaxation of the muscles. The dog is placed on its back, one person pulls it forward by the front legs, another stretches the hind legs and turns them inward at the same time. The image must be absolutely symmetrical, apart from the hip joints and the iliac wings, the knee joints and kneecaps must also be completely in the picture.

In order to be able to evaluate the recording, the veterinarian must have some experience, at least with the lighter grades, whereby the signs of severe HD can often already be recognized by laypeople. The so-called "official" recordings must be sent to a central evaluation point for evaluation, which differs depending on the breed club.
As early as 1965, the first clubs introduced a breeding ban for dogs with medium and severe HD; since then, the importance of x-rays has not changed, either for diagnostic reasons on a veterinary level or for prophylactic reasons on a breeding level. Until recently, only veterinarians authorized by the relevant breed clubs were allowed to take official recordings, today the situation is such that every veterinarian is officially allowed to take HD X-rays, but is of course also responsible for correct storage and the quality of the recording. Under certain circumstances it can happen that images from the central evaluation point are returned as not evaluable and new recordings have to be made. The "unofficial" recordings, such as the pre-X-ray, should be made just as conscientiously as the official recordings in order to be able to make a reliable statement.
This pre-X-ray at the age of seven to nine months makes sense if a working dog owner wants to know whether the beginning of intensive training for the dog is acceptable from a veterinary point of view, or whether there are already corresponding changes in the hip joints. Of course, a statement at this age can only be made with reservations, specific information on the condition of the hip joints with regard to HD can only be made after the epiphyseal has finished growing, for this reason the time of the official X-ray is never before the end of the twelfth month of life.
As mentioned earlier, diagnosing HD based on X-rays requires a certain amount of experience on the part of the veterinarian. There are certain criteria for assessing the severity that the evaluator must also be familiar with. The position, the shape of the socket, the shape of the head of the femur, the position of the head in the socket, the neck of the femur and the joint space must be assessed.
In addition, the so-called NORBERG angle is measured. This measurement, which is carried out directly on the X-ray using a special template, allows an additional objective assessment of the hip condition. A value of 105 ° or more is desirable; lower values indicate flat pans or loose hips.

Of course, there are race-related anatomical differences in the hip joint that the assessor should be aware of. Chondrodysplastic breeds such as Basset, Dachshund and sometimes Cocker Spaniel are to be assessed differently than breeds with normal bone and cartilage growth such as German Shepherd Dog, Doberman, Hovawart, etc. Large breeds such as St. Bernard or Great Danes should also be X-rayed later than smaller breeds, because their bone growth is accordingly completed later. An age of 18 months is a guideline.

Depending on the extent of the radiographically detectable changes, a classification is made into different degrees of severity. These are normal (A) for joints with a NORBERG angle of 105 ° or more, almost normal, transition or HD suspicion (B) with minor changes in the head or socket and a NORBERG angle of at least 100 ° . Slightly more pronounced deviations can be found in slightly (C), as well as incongruence and possibly a diverging joint space. The NORBERG angle is around 100 °. With moderate HD (D) there are more serious changes with arthritic growths. The NORBERG angle is between 90 ° and 100 °. Finally, in severe HD (E) the entire joint is severely changed. There may be a complete dislocation, at first glance you can see the arthritic changes and the NORBERG angle is less than 90 °.

X-rays are therefore the most important means of diagnosing an existing HD. However, since not every dog is routinely x-rayed, we would also like to point out possible clinical symptoms that can occur with existing HD. Mind you, because even with a medium to severe HD according to the X-ray image, it can happen that the dog moves without major problems and is also pain-free. Last but not least, this should be a reason to have your dog X-rayed in any case, even if it is not a pedigree dog or an animal intended for breeding. In most cases of manifest HD, there are symptoms that the dog owner will notice and also cause him to visit the vet. These include primarily signs of lameness in the hindquarters, pain during both active and passive movement, and difficulty getting up.
Very often, especially in predisposed breeds such as the German Shepherd Dog, Rottweiler, etc., any movement disorder or pain in the pelvic area is already interpreted by the owner as HD. However, in order to differentiate between other diseases that can also occur in these breeds, a veterinary examination including an X-ray is essential.

HD Grade and their meaning:

HD - A1 HD- A2
No reference to HD


HD- B1 HD- B2
Borderline case, transitional form


HD- C1 HD- C2
Light HD


HD- D1 HD- D2
Medium HD


HD-E1 HD-E2
Heavy HD


The number after the degree stands for the tendency towards the previous or next degree.


The Cane Corso is approved for breeding in Germany up to HD-C.