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Old Dog Resources
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CANINE HIP DYSPLASIA (CHD)
...and Degenerative Joint Disease (DJD)
by T. J. Dunn, Jr. DVM
 HIP DYSPLASIA in dogs! With this report
we'll clear up some misconceptions, describe what CHD is, what effect the
condition can have on the dog and what can be done about it. Because
Hip Dysplasia in dogs is a complex topic, it requires extensive
consideration in order to have a good understanding of its nature. Cats do
suffer from Hip Dysplasia, too, but it is seen less frequently in cats.
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WHAT IS IT: "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".
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. 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.
Some of the environmental aspects that can affect the observable expression of
hip dysplasia are the following:
1. Nutrition - There are reports that in puppies a restricted calorie
intake could restricted the growth rate, and in turn will lessen the potential
for the dog to develop hip dysplasia. (I wouldn't suggest doing this to any
pup... it makes as much sense as stealing money from your own checking
account!) The problem is that some restricted diets restrict the fat and
protein content and increase the carbohydrate content of the food. Bad! See a
better way in the discussion in ThePetCenter.com
here.
The real goal should be to keep growing pups from becoming OVERWEIGHT.
Restricting fat and protein in a growing pup can be a disaster. A high quality,
meat-based diet is absolutely necessary for growing pups, just don't feed so
much of it that the pup becomes overweight.
2. Physical Activity - In a young, growing dog with a genotype (genetic
makeup) for CHD who will eventually develop some trouble because of it, will
develop more arthritis and have more eventual difficulty if it is highly active
physically. Climbing stairs, jumping into and out of pick-up trucks, running
with other normal dogs can all subject the growing hip structures to unwarranted
stress and trauma and increase future discomfort for the dog. The effects of
this excessive activity is worsened in an overweight pup. (In a normal, growing
dog, all these activities will not cause hip dysplasia!)
3. Bedding - There is no scientific proof,
but lots of observational conclusions, that pups reared especially during the
nursing period on slippery surfaces such as newspapers will be prone to hip
difficulties. That is not to say that smooth concrete, wood or newspaper
surfaces cause dysplasia, just that they can make a bad situation worse.
Better surfaces for newborn pups would be blankets or towels... something they
can get a better grip on.
MUSCLE AND CHD: Research has shown that dogs with CHD have significantly
decreased sizes of total pelvic musculature surrounding and acting on the hip
joint. Whether this is a contributing factor or a result of hip dysplasia
remains to be proven.
One muscle that can contribute to worsening of hip dysplasia is the Pectineus
Muscle. In dogs with a strong genetic background for CHD, the microscopic
makeup and contractibility of the Pectineus Muscle are strikingly different from
the same muscle of normal dogs. The theory is that a tight or inelastic
Pectineus Muscle causes tension in such a direction that the force tends to pull
the head of the femur away from the acetabulum. So the tight muscle creates
more looseness in the joint. I have had good results in about 50% of the cases
I have surgically excised a portion of the Pectineus Muscle. The patients were
more comfortable and mobile almost immediately. This Pectineal Myotomy surgery
has no effect on the arthritic changes in the hip joints; it can make the dog
more comfortable.
LIGAMENT OF THE HEAD OF THE FEMUR: Attaching to the head of the femur
from the center of the hip socket is a tough fibrous ligament called the
Ligament of the Head of the Femur. If this ligament is stretched or torn, the
hip joint will be less stable . . . and this is exactly what happens to dogs
with dysplasia. In fact, some of the first changes to take place in young dogs
developing hip dysplasia occur in this ligament especially if the muscle mass of
the pelvis is underdeveloped. The ligament swells, develops tiny tears and
stretches. In advanced CHD this ligament can totally break down and cause more
harm than good.
JOINT CAPSULE: This tissue, which if you could hold it, would feel like
the wall of a thick balloon It surrounds the joint and produces synovial fluid
to nourish and lubricate the joint cartilage. In addition, the joint capsule
provides some support to the joint.
In dysplastic joints the capsule becomes irritated, stretched, and scarred. In
advanced cases the capsule will lose its elasticity and inhibit a full range of
motion in the joint. A large percentage of the pain associated with hip
dysplasia originates from inflamed nerve endings in the joint capsule so any
pathology here will have a noticeable affect on the dog.
CARTILAGE: The surfaces of the head of the femur and the acetabulum are
covered with what is termed hyaline cartilage. In a dysplastic joint the points
of pressure and the amount of pressure applied to areas of cartilage surfaces
are abnormal. The cartilage is being asked to do things it physically cannot
accomplish, so it changes or disintegrates as a response. The changes range from
thickening in abnormal areas to thinning in others. Sometimes the pounding it
gets erodes the cartilage down to the underlying bone! The outcome is more pain
and discomfort, more inflammation, more calcium deposits from inadequate healing
attempts and eventual breakdown of the joint as a unit. Nutriceuticals such as
Chondroitin Sulfate and Glucosamine may be effective in aiding the repair and
maintenance of this articular cartilage.
BONE CHANGES: Since bone is alive it responds to stress and grows in a
manner that tends to distribute weight loads evenly. As a result of posture
changes brought on by discomfort, the dog's weight bearing forces stress the
bone in
unnatural ways. The bone does what it is supposed to do as a response and
changes its shape. The bone doesn't know doesn't know that the shape it changes
to is abnormal.
Ultimately, this abnormal shape to the thigh bone and acetabulum create more
difficulty with stability and a vicious cycle ensues that spells trouble for the
dog. See the images below for a comparison of before/after bony changes. The
final outcome of bony remodeling in unstable hip joints is Degenerative Joint
Disease.
SIGNS OF CHD IN YOUNG DOGS: What you will see first is a pup that runs
with both back legs nearly together, almost like a rabbit would run. After
exercise the pup will be reluctant to rise, will sit back as if unsteady and
will have difficulty climbing stairs or inclines. The pup might look slightly
underdeveloped in the rear quarters. When it stands the rear legs may not be
parallel, but rather too near each other at the hocks (ankles) called "cow
hocked".
You might notice a boniness to the pelvic area from lack of good muscle
development. Another hint of trouble is an inability to extend the leg
backward very far (decreased range of motion). Note: Many pups rest or sleep in
a frog-like position with knees extended out to either side - this is a good
sign and shouldn't alarm you.
In severe cases of dysplasia, the young dog will rock forward to support more
weight on the front legs (which can create trouble in the shoulders and
elbows). When dogs do this it seems as if they are tip-toeing or walking very
lightly on their rear legs. A dysplastic pup will be reluctant to jump or
"stand up" on its hind legs. Signs usually
being between five and eights months of age. But remember, as we learned above,
some dogs do not show any signs at all of hip joint degeneration until mature
adults.
AN INTERESTING CASE: Here is
a classic example of why it is so important to take a radiograph of the sire and
bitch prior to
breeding.
In this example the owner had a two year old male Golden Retriever that was
totally healthy by any observable standards. It ran, jumped, swam and had never
showed any kind of lameness. The owner had the dog x-rayed and guess what? The
film displayed severe abnormalities in the left hip joint. Were the changes due
to a genetic propensity for hip joint abnormalities? Or was this actually due
to an injury early in the pup's life that impacted the proper growth of the
joint structures? No one can say for certain. But IF the abnormal hip was due
to genetic determiners why take a chance that, if bred, the litter might have
even worse hip joint conformation? The owner decided not to breed the dog.
SIGNS OF CHD IN OLDER DOGS: Some dogs with dysplasia escape pain or
simply accept it as a fact of life and don't complain until degenerative joint
disease sets in. Affected dogs will sit rather than stand, have trouble
arising, run with the rear legs together and not be able to keep up any more on
Sunday walks. Every veterinarian has been mystified on occasions where an x-ray
of an older dog, who only recently seemed to be having hip trouble, reveals
extensive degenerative changes in the hips due to long term dysplasia.
It is very important to keep this fact in mind: A dog can appear normal and yet
have hip dysplasia. Just because a four-year-old dog isn't showing signs of
trouble is not sufficient evidence to state "it couldn't possibly have hip
dysplasia". I have heard supposedly responsible breeders make that statement
and it takes lots of convincing to get them to believe otherwise.
If you are involved with a breed in which CHD has been reported, and you wish to
improve the breed as well as have happy owners of your pups you must know if
your breeding stock is prone to CHD. And neither you, your cousin, the mailman
OR your veterinarian can tell if your dog has CHD unless some basic guidelines
are followed.
DETERMINING THE PRESENCE OF CHD: Dogs with obvious signs of CHD (hip
soreness, difficulty arising or climbing inclines, muscle atrophy over the rump,
limping) are not a challenge to confirm as such. So this discussion will apply
more to the dog that seems to be normal but you are either not sure or
need to know for breeding or training/working reasons. The minimum data
required is a pelvic x-ray taken under anesthesia . . . PERIOD! You MUST have
the x-ray to know if the dog is normal!
PennHIP: (University of Pennsylvania
Hip Improvement
Program) See
an entire article about PennHIP
here. Commercially available since 1993, this procedure has been and was developed as
an objective method of evaluating dogs’ hip structure. It evolved as a
direct result of the subjectivity factors and age constraint (maturity)
limitations inherent to evaluation and certification of dogs by the OFA and
other screening programs. PennHIP research published in peer reviewed journals
has shown that different breeds have different susceptibility to
osteoarthritis. Therefore, in PennHIP evaluations each breed is compared to its
own. Only PennHIP certified veterinarians can do the PennHIP evaluation but many
veterinarians are becoming certified in this procedure.
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 Why is anesthesia required in order to have the
dog radiographed? To have an x-ray that yields the information you're trying to
discover the dog must be perfectly relaxed. Because the position required to
take a diagnostic x-ray is a somewhat unnatural one, even very gentle,
cooperative dogs cannot relax enough to be x-rayed properly. See the x-ray on
the right. It is a great example of poor positioning. The dog is tilted to its left (to our right) and the view we see of
the structures is imbalanced. One hip looks OK and the other bad but in reality
this view is worthless. Nothing is more frustrating for the veterinarian than to
have an owner say "I need to know if this dog has any signs of hip dysplasia.
Take an x-ray, but I don't want you to use anesthesia; this dog will do anything
you tell it to do, so an anesthetic isn't necessary." Unless at the time of
exposure of the x-ray, the dog is positioned precisely, with no movement, the
x-ray will not be credible. You won't get the information you need! Your
veterinarian will look for an x-ray image that looks like the nice, normal hip
at the beginning of this article.
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Another great advantage of
anesthesia is that the veterinarian can only then palpate and manipulate the
hips to actually feel the degree of looseness. Also, the tension of the
Pectineus Muscle is best assessed under anesthesia. Any grating or grinding
from calcium deposits along the hip joints can be evaluated better than
attempting to do so on an awake patient. If you need the information, the dog
needs the anesthetic.
If the pelvis is tipped only slightly to one side or the other, one hip can
appear normal that isn't and one can appear dysplastic that isn't! To
complicate things, 10% of dysplastic dogs will be affected in only one hip!
Better do the x-ray right!
The importance of radiography cannot be overstated. It can be done early, say
five or six months of age, if dysplasia is suspected. If the results are
questionable, reserve breeding until a time when the x-rays are conclusive.
Generally, by the time the dog is full grown the x-rays will properly reveal the
status of the hips. The OFA (OFA.org) will not classify hips in dogs until they
are two years of age.
The advantage of radiography in a younger animal is that if you plan on breeding
it you can eliminate fruitless time and financial and emotional expense related
to breeding if the x-rays show unquestionable hip dysplasia. There have been
many disappointed, depressed dog owners whose expectations for breeding were
high and were shocked back to reality when their two-year-old dog showed x-ray
evidence of dysplasia... two years of planning, training and dreams of great
litters down the tube. If only the parents had been x-rayed. If only
preliminary x-ray were taken eighteen months ago. Again, the advantage of the
PennHIP procedure is obvious since dog over 4 months of age cane be evaluated.
It is very sad indeed for any pet
owner to see their special pal affected by the discomfort and mobility problems
associated with Canine Hip Dysplasia. Fortunately, armed with knowledge and
forethought, highly selective breeding is your best defense against CHD.
I have seen a
number of breeders who sold litters of pups where the sire and bitch
had not been x-rayed for CHD. The breeders were shocked a
year or so later when the phone started ringing and upset dog
owners complained because "that pup you sold us has hip dysplasia
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Special thanks to Dr. Dunn for permission to reprint this information!
Visit Dr Dunn at ThePetCenter.com
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Another great
article on Hip Dysplasis from Drs. Foster
& Smith |
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