Canine Hip Displasia |
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Canine hip dysplasia (CHD) is a developmental trait primarily affecting medium and large breed dogs but it is also known | |||||||||||||||||||||||||||||||||
in Cardigan Welsh Corgis. Many Cardis who are diagnosed with affected hips however do not seem to suffer a lot from | |||||||||||||||||||||||||||||||||
this defect and manage to live their life to the max. | |||||||||||||||||||||||||||||||||
CHD is characterized by faulty conformation and laxity of the hip joint that usually affects both hips. It can be detected | |||||||||||||||||||||||||||||||||
radiographically as subluxation of the affected hip. The eccentric load on the articular surface of the femoral head (ball) | |||||||||||||||||||||||||||||||||
and acetabulum (socket or cup) leads to erosion of the cartilage, inflammation in the joint, and debilitating pain. Clinically, | |||||||||||||||||||||||||||||||||
the osteoarthritis or degenerative joint disease that results from hip dysplasia is characterized by hind limb lameness, | |||||||||||||||||||||||||||||||||
reduced exercise tolerance, reluctance to jump, and poor hind limb muscle mass. | |||||||||||||||||||||||||||||||||
There are several methods for scoring CHD. In The Netherlands the x-rays are rated by a panel of three expert evaluators | |||||||||||||||||||||||||||||||||
assigned for this task by the Dutch Kennelclub, this department is known as GGW (Health, Behaviour and Wellbeing). | |||||||||||||||||||||||||||||||||
Cardis can be evaluated from the age of 12 months. In the Netherlands we get an evaluation based on FCI regulations. | |||||||||||||||||||||||||||||||||
Because of this it should be possible to compare the scores between the different countries. Today we still see different | |||||||||||||||||||||||||||||||||
scores in our breed in certain FCI countries, it raises the question whether the hips of these dogs are of less quality or if | |||||||||||||||||||||||||||||||||
there is a different method of scoring within the FCI countries. | |||||||||||||||||||||||||||||||||
Then there is the Orthopedic Foundation for Animals that scores hips. Many Cardigan hips have been evaluated by the | |||||||||||||||||||||||||||||||||
OFA and many results can be found in the OFA’s database. | |||||||||||||||||||||||||||||||||
The phenotypic evaluation of hips done by the Orthopedic Foundation for Animals falls into seven different categories. | |||||||||||||||||||||||||||||||||
Those categories are Normal (Excellent, Good, Fair), Borderline, and Dysplastic (Mild, Moderate, Severe). Once each of | |||||||||||||||||||||||||||||||||
the radiologists classifies the hip into one of the 7 phenotypes above, the final hip grade is decided by a consensus | |||||||||||||||||||||||||||||||||
of the 3 independent outside evaluations. Examples would be: | |||||||||||||||||||||||||||||||||
Two radiologists reported Excellent, one Good—the final grade would be Excellent | |||||||||||||||||||||||||||||||||
One radiologist reported Excellent, one Good, one Fair—the final grade would be Good | |||||||||||||||||||||||||||||||||
One radiologist reported Fair, two radiologists reported Mild—the final grade would be Mild | |||||||||||||||||||||||||||||||||
The hip grades of Excellent, Good and Fair are within normal limits and are given OFA numbers. This information is | |||||||||||||||||||||||||||||||||
accepted by AKC on dogs with permanent identification and is in the public domain. Radiographs of Borderline, Mild, | |||||||||||||||||||||||||||||||||
Moderate and Severely dysplastic hip grades are reviewed by the OFA radiologist and a radiographic report is | |||||||||||||||||||||||||||||||||
generated documenting the abnormal radiographic findings. Unless the owner has chosen the open database, | |||||||||||||||||||||||||||||||||
dysplastic hip grades are not in the public domain. | |||||||||||||||||||||||||||||||||
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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 (femoral head) which fits tightly into a well-formed socket (acetabulum) with minimal | |||||||||||||||||||||||||||||||||
joint space. There is almost complete coverage of the socket over the ball. | |||||||||||||||||||||||||||||||||
Good: slightly less than superior but a well-formed congruent hip joint is visualized. The ball fits well into the socket and | |||||||||||||||||||||||||||||||||
good coverage is present. | |||||||||||||||||||||||||||||||||
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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. This can be a normal finding in some breeds however, such as the Chinese Shar Pei, Chow Chow, and Poodle. | |||||||||||||||||||||||||||||||||
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 Hip Dysplasia: 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. Since HD is a chronic, progressive disease, the older the | |||||||||||||||||||||||||||||||||
dog, the more accurate the diagnosis of HD (or lack of HD). | |||||||||||||||||||||||||||||||||
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Moderate Hip Dysplasia: 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. Once arthritis is reported, there is only continued progression of arthritis over time. | |||||||||||||||||||||||||||||||||
Severe Hip Dysplasia: 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. | |||||||||||||||||||||||||||||||||
Here is a table that shows the different scoring methods. | |||||||||||||||||||||||||||||||||
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Then there is the PennHIP method. To go short: The PennHIP method is a novel way to assess, measure and interpret | |||||||||||||||||||||||||||||||||
hip loint laxity. It consists of three separate radiographs: the distraction view, the compression view and the | |||||||||||||||||||||||||||||||||
hip-extended view. The distraction view and compression view are used to obtain accurate and precise measurements | |||||||||||||||||||||||||||||||||
of joint laxity and congruity. | |||||||||||||||||||||||||||||||||
The hip-extended view is used to obtain supplementary information regarding the existence of osteoarthritis | |||||||||||||||||||||||||||||||||
(OA) of the hip joint. (The hip-extended view is the conventional radiographic view used to evaluate the integrity of the | |||||||||||||||||||||||||||||||||
canine hip joint.) The PennHIP technique is said to be more accurate than the current standard, and it has been shown | |||||||||||||||||||||||||||||||||
to be a better predictor for the onset of OA. | |||||||||||||||||||||||||||||||||
The radiographs pictured here are of the same dog, yet the hip joint laxties in each view look very different. Notice that | |||||||||||||||||||||||||||||||||
the hips in the distraction view appear to be much looser than they do in the hip-extended view. | |||||||||||||||||||||||||||||||||
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To summarize, PennHIP method: | |||||||||||||||||||||||||||||||||
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Obtains OA readings from the standard hip-extended view | ||||||||||||||||||||||||||||||||
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Obtains hip joint congruity readings from the compression view | ||||||||||||||||||||||||||||||||
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Obtains quantitative measurements of hip joint laxity from the distraction view | ||||||||||||||||||||||||||||||||
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CHD in dogs is an inherited, polygenic trait in which mutations in several genes called quantitative trait loci (QTLs) | |||||||||||||||||||||||||||||||||
contribute to its clinical expression. Many dogs with normal hips on radiographs carry at least a modicum of the trait- | |||||||||||||||||||||||||||||||||
causing mutations but not all that are necessary to cause physical expression of the trait. CHD is a quantitative or | |||||||||||||||||||||||||||||||||
complex trait that is expressed as a continuum from imperceptible to severe forms. This continuum of trait expression is | |||||||||||||||||||||||||||||||||
due to environmental influences (such as plane of nutrition and exercise, as well as other unknown factors) which | |||||||||||||||||||||||||||||||||
interact with the genetic constitution to affect the degree to which the trait is manifested. | |||||||||||||||||||||||||||||||||
CHD has a heritability between 0.20-0.7. This means that between 20 and 70% of the physical appearance of the hips | |||||||||||||||||||||||||||||||||
of each dog in a pedigree can be attributed to its genetic relationships within the pedigree. | |||||||||||||||||||||||||||||||||
It will take a concerted effort to rid breeds of the genetic mutations that cause CHD or conversely, to introduce | |||||||||||||||||||||||||||||||||
protective alleles at the loci that cause good hips. Selective breeding based on current radiographic methods can | |||||||||||||||||||||||||||||||||
reduce the frequency of CHD in a population. Breeding two dysplastic dogs can yield a 75% incidence of hip | |||||||||||||||||||||||||||||||||
dysplasia in offspring, while mating two unaffected dogs can yield a 25% incidence of the disease. Selective | |||||||||||||||||||||||||||||||||
breeding using normal dogs from normal parents and grandparents, as well as progeny testing, should decrease the | |||||||||||||||||||||||||||||||||
incidence of CHD. | |||||||||||||||||||||||||||||||||
Until there is a genetic test for CHD, so we can detect genetically susceptible dogs, the best indication of a dog's | |||||||||||||||||||||||||||||||||
genetic makeup is where it came from (its' parents and grandparents), what it produces (its' offspring), and the | |||||||||||||||||||||||||||||||||
phenotype of its' siblings or half sibs. Dogs with normal hip radiographs that carry some of the mutations that cause | |||||||||||||||||||||||||||||||||
CHD but perhaps not the major ones, when bred to a mate that also carries some of the mutations for CHD, may | |||||||||||||||||||||||||||||||||
produce affected offspring. | |||||||||||||||||||||||||||||||||
To test whether a dog carries some of the mutations (even if the dog has OFA-good hips), it should be bred to sires | |||||||||||||||||||||||||||||||||
or dams with good hips and the proportion of affected offspring recorded (progeny testing). As many as 15-20 | |||||||||||||||||||||||||||||||||
offspring should be produced to be reasonably sure that the parents do not carry important mutations. This is an | |||||||||||||||||||||||||||||||||
unreasonable burden for dog breeders to bear. Breeders should attempt to breed dogs with the best hips in | |||||||||||||||||||||||||||||||||
their colony as well as to dogs with the other optimal breed characteristics and temperament. | |||||||||||||||||||||||||||||||||
At the Cornell University Hospital for Animals in New York they have been searching for the genes that contribute | |||||||||||||||||||||||||||||||||
to hip dysplasia. When an owner comes to this hospital for hip radiographs, they are asked to donate a small | |||||||||||||||||||||||||||||||||
sample of blood from their dog for DNA isolation. This DNA and the hip radiograph measurements are then used | |||||||||||||||||||||||||||||||||
later to discover and confirm the mutations that contribute to hip dysplasia. Once they know which genes and | |||||||||||||||||||||||||||||||||
biochemical pathways lead to good and poor hip conformation, they can develop novel treatments which can be | |||||||||||||||||||||||||||||||||
applied at an early age. | |||||||||||||||||||||||||||||||||