Hip Dysplasia is a genetic disease due to an abnormally developed hip joint. The cartilage that lines the joint is damaged which causes this cartilage to loose it's ability to absorb the load that is placed on the joint during movement. As the disease progresses there is inflammation and the dog's body produces new bone at the edges of the joint surface, joint capsule, ligament and muscle attachments. The joint capsule also eventually thickens and the joint's range of motion decreases.
No one can predict when or even if a dysplastic dog will start showing signs of lameness due to pain. There are multiple environmental factors such as caloric intake, level of exercise, and weather that can affect the severity of lameness and radiographic changes. There is no rhyme or reason to the severity of radiographic changes correlated with the severity of lameness. There are a number of dysplastic dogs with severe arthritis that run, jump, and play as if nothing is wrong and some dogs with barely any arthritic radiographic changes that are severely lame. Since HD is a chronic, progressive disease, the older the dog, the more accurate the diagnosis of HD (or lack of HD).
Some veterinarians OVERREACT to a diagnosis of HD, recommending expensive and invasive surgeries (Triple Pelvic Osteotomy, Total Hip Arthroplasty or Pectineus Tendon Surgery) when most cases can be managed with natural supplements that have no harmful side effects (MSM, Ester-C, Chondroitin, Glucosamine, Perna Mussel etc.). If you bought your dog from a reputable breeder and your dog is well bred with multiple generations of cleared ancestry, the severity of the disease is ofton mild and is is rare that such extreme measures are needed to manage the disease. It is much more common to see severe forms of the disease in dogs purchased from back-yard breeders, puppy mills and puppy farmers. If your dog is diagnosed with HD - DON'T PANIC. Talk to your breeder or someone that is knowledgeable and familiar with HD and various management options before jumping into invasive or expensive treatments or surgeries.
Excellent - this classification is assigned for superior conformation in comparison to other animals of the same age and breed. There is a deep seated ball which fits tightly into a well-formed socket with minimal joint space. There is almost complete coverage of the socket over the ball.
Good - slightly less than superior but there is a well-formed congruent hip joint. The ball fits well into the socket and good coverage is present. Statistically, most Rottweilers with normal ratings will fall into this category.
Fair - Assigned where minor irregularities in the hip joint exist. The hip joint is wider than a good hip phenotype. This is due to the ball slightly slipping out of the socket causing a minor degree of joint incongruency. There may also be slight inward deviation of the weight-bearing surface of the socket (dorsal acetabular rim) causing the socket to appear slightly shallow.
Borderline - there is no clear cut consensus between the radiologists to place the hip into a given category of normal or dysplastic. There is usually more incongruency present than what occurs in the minor amount found in a fair but there are no arthritic changes present that definitively diagnose the hip joint being dysplastic. There also may be a bony projection present on any of the areas of the hip anatomy illustrated above that can not accurately be assessed as being an abnormal arthritic change or as a normal anatomic variant for that individual dog. To increase the accuracy of a correct diagnosis, it is recommended to repeat the radiographs at a later date (usually 6 months). This allows the radiologist to compare the initial film with the most recent film over a given time period and assess for progressive arthritic changes that would be expected if the dog was truly dysplastic. Most dogs with this grade (over 50%) show no change in hip conformation over time and receive a normal hip rating; usually a fair hip phenotype.
Mild - there is significant subluxation present where the ball is partially out of the socket causing an incongruent increased joint space. The socket is usually shallow only partially covering the ball. There are usually no arthritic changes present with this classification and if the dog is young (24 to 30 months of age), there is an option to resubmit an radiograph when the dog is older so it can be reevaluated a second time. Most dogs will remain dysplastic showing progression of the disease with early arthritic changes.
Moderate - there is significant subluxation present where the ball is barely seated into a shallow socket causing joint incongruency. There are secondary arthritic bone changes usually along the femoral neck and head (termed remodeling), acetabular rim changes (termed osteophytes or bone spurs) and various degrees of trabecular bone pattern changes called sclerosis.
Severe - assigned where radiographic evidence of marked dysplasia exists. There is significant subluxation present where the ball is partly or completely out of a shallow socket. Like moderate HD, there are also large amounts of secondary arthritic bone changes along the femoral neck and head, acetabular rim changes and large amounts of abnormal bone pattern changes.
Unfortunately, most inherited traits, including inherited diseases, are polygenic - which means that multiple genes are involved in the inheritance of the trait and both the sire and dam must contribute one or more of the genes that cause the trait to appear in the offspring. Because a trait can skip generations it may appear to be erratic in it's occurrence.
Dogs that are known to be dysplastic should not be bred. According to Cornell University, College of Veterinary Medicine, Baker Institute of Animal Health, the breeding of two affected dogs produces an incidence of 75 percent in offspring – in other words, 3 out of 4 puppies produced by two dysplastic dogs will themselves develop hip dysplasia. In contrast, on average only 25 percent of offspring of a mating between two healthy dogs will develop hip dysplasia. There is clearly an advantage to a mating between normal dogs. By limiting the breeding population to only those dogs with healthy hips, we can lower the number of new cases of hip dysplasia that will appear in the coming generations.
To date, no DNA tests have been developed to identify the specific combination of mutant genes responsible for any polygenic disorders. Therefore, breeders must rely on phenotypic evaluations (the external expression of a trait) to make informed decisions regarding a dog's suitability for breeding purposes. It is only through testing of individual dogs for the presence of hip dysplasia and knowledge of the prevalence of the hip dysplasia in bloodlines, related dogs and offspring that a breeder can reduce the incidence or severity of the problem.
Examination of over 3700 dogs in Switzerland has proven that 42% of all purebred dogs there are affected by HD despite control programs for the last 30 years. Breeding with dysplastic dogs and lack of progeny control are responsible for this slow progress. [M. Fluckiger, J. Lang, H. Binder, et al. [The control of hip dysplasia in Switzerland. A retrospect of the past 24 years]. Schweiz Arch Tierheilkd, 1995;243-50.]
Genetic hip dysplasia can not be caused by environment but environment (diet, exercise, supplementation) can make hip dysplasia more or less evident or problematic. While there are certainly other problems that can mimic the symptoms of hip dysplasia (hip or pelvic injury, cruciate ligament tear, panostiotis, normal arthritic changes due to age or excessive wear and tear on a joint etc.) a dog will not develop genetic hip dysplasia if it does not have the genes necessary to produce the trait.
There are countless ongoing HD studies that are examining everything from the role of nutritional and environmental factors to the time of year that a dog is born. Environmental factors can definitely contribute to the age of onset of lameness and the severity of changes or lameness. It is very clear from the existing studies that there is a higher incidence of HD in overweight dogs and dogs fed excess calcium during growth but more information is definitely needed to determine if the obesity or nutrient imbalance is the cause of the HD or if the obesity or calcium simply causes the HD to become evident at an earlier age. Either way, overfeeding, obesity and improper diet definitely have a negative impact on HD.
Click here for an excellent article on the role of environment on hip dysplasia by Dr. Mary C. Wakeman, D.V.M.
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