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Hip Dysplasia
Text and X-rays from the Pet Center.com
"Hip dysplasia" simply stated means an
"abnormal formation" of the hip joint. Think of the condition
first as a looseness in a joint that should be snug - then most of the
problems attendant to hip dysplasia are a result of this
"looseness". See the image on the right a few
paragraphs down for an example of a nice, normal, snug hip joint.
The normal anatomy of the hip joint is a classic Ball and Socket joint.
The head of the femur (the "Ball") is supposed to match the
acetabulum (the "Socket"). A good hip joint has a neat,
snug fit between the ball and socket - that is, the head of the femur
should not be slipping and slopping around somewhere in the neighborhood
of the acetabulum!
There are infinite variations of dysplasia - ranging from only very slight
changes from normal to complete dislocation. (There are a number of
examples of actual radiographs in the table near the bottom of this page.
Click on any x-ray image to enlarge it.) Consequently, no two dogs
will be affected by CHD exactly alike.
HOW IS CHD ACQUIRED? This is one disorder that has been
proven, positively, to have a genetic basis. How much of a genetic
origin in each case can vary from 25% to 85%. A condition that
is completely determined by genetics, for example gender, has a
Heritibility Factor of 1. A condition totally unaffected by
genetics, for example a broken leg, has a Heritibility Factor of zero.
Studies have shown that CHD's Heritibility factor ranges from .25 to .85;
this is a significant genetic contribution. So the Heritibility
Factor for a given dog is the result of a combination of the Heritibility
Factors from each parent. Simply put . . . if the parents are
carrying genetic material for hip dysplasia - so will the
offspring. And the greater the genetic contribution for loose
hips or malformed bone or abnormal muscle mass (Heritibility Factor) from
the parents, the greater the chances for hip dysplasia in the offspring.
The expression of hip dysplasia in any dog has other determinants, though;
genetics play only a varying role in the total picture. The effect
of the developing dog's environment does play a role in the clinical
(observable) signs of dysplasia, although just like the genetic component
the effects of environment are variable and not completely understood.
To illustrate the complexity of the environmental issue, listen to this:
It is possible for a dog with known genetic components for hip dysplasia
(called genotype) to not show any clinical signs of trouble if the
environmental factors are favorable. So the dog can be dysplastic and not
show observable signs of it until middle or old age. I have seen
this fairly commonly in practice and it is always an important issue with
breeders who assume that their dog is normal just because it hasn't shown
any signs of hip trouble. Why take pelvic x-rays for dysplasia when
the dog has always acted perfectly fit, they reason. There is no
excuse for NOT taking pre-breeding x-rays. I have seen a number
of breeders who sold litters of pups where the parents have not been
x-rayed for CHD and who were shocked a year or so later when the phone
started ringing about "that pup you sold has hip dysplasia".
Trust me, it happens. Also, if two dogs that have the same genotype
(genetic makeup) are exposed to different environmental conditions, their
expression of hip trouble can be quite dissimilar. Little wonder
that the topic has such a wide range of information and misinformation
regarding it.
More information about hip dysplasia - The
Pet Center.com
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