HIP DYSPLASIA

Literally, hip dysplasia (HD), means "badly formed hip". In order to understand this complex problem it is necessary to be aware of the structure of the canine hip. The ball and socket joint consists of two basic parts - the acetabulum and the femur. The femur, or thigh bone, consists of the head (the ball) and the neck (the part of the femur that joins the long shaft of the bone to the head). The acetabulum forms the socket part of the joint and it is in this socket that the head of the femur rests.



In unaffected dogs there is a good fit between ball and socket. An easy way to think about it is to imagine a tennis ball and a cup. If you put the ball into the cup there is a good fit. If you put the ball into a saucer, it will roll around loosely. This poor fit between femoral head and acetabulum is characteristic of dysplastic dogs.

Affected dogs are not born with HD, only with the makings of it. As puppies grow, laxity of the muscles and ligaments surrounding the joint and the poor fit between the bones produces excess movement of the ball in the acetabulum. The separation between the bones is called subluxation, and at its most severe it can become a total dislocation (the head of the femur leaves the acetabulum). The surfaces of the bones start out completely smooth, but with HD changes take place. Bone rubbing against bone causes irritation which results in irregular bone growth and wear on the articular surfaces. These irregular surfaces result in Osteoarthritis, which can cause significant pain. As the bone of the acetabular rim is ground away, the socket becomes shallower and it is more difficult to keep the head of the femur properly seated.

Outward signs of hip dysplasia can range from none to severe pain. The dog's movement may or may not be affected. Some outward signs that MAY be seen in affected dogs are:

Difficulty getting up from a lying or sitting position or in climbing stairs.
A bunny hop gait (moving both rear legs together).
A painful reaction to extension of the rear legs.
Pushing on the rump may cause the pelvis to drop.
When rolled over, some affected dogs will resist having their legs spread into a frog-leg position.
A side to side sway of the rump.
Dogs may avoid jumping
Lameness may be seen, especially after strenuous exercise.
It is very important to understand that the only way to accurately diagnose HD is through x-rays, since the above symptoms may also be seen in dogs with normal hips; furthermore, affected dogs may display none of these symptoms at all.

The X-ray photographs below illustrate various degrees of severity of the dysplastic condition. The normal hips on the left are free of dysplasia, as shown by the tight and full fit of the ball in the socket, and by the U-shaped notch in the neck; the hips on the right exhibit mild dysplasia in the right hip, as evidenced by the slight flattening of the head of the femur and by the socket not being as round as it could be.



  Normal Hips Mild Dysplasia on Right Side
The x-ray photographs below both show a severe degree of dysplasia, accompanied by degenerative joint disease, and the effects of the wearing away of both the ball and the socket (acetabulum) can be clearly seen. In both of these cases the dog in question would have experienced difficulty in movement and probably a very great deal of pain and discomfort. In the picture on the left, the arrows point to the thickened femoral neck on each side, as well as the secondary arthritis occurring on the left hip. Note the flat sockets and the non-rounded appearance of the femoral head. The extreme case on the right is nearly as bad as it gets, causing crippling lameness and severe pain.

     NORMAL HIPS                    MILD HD RIGHT HIP                    EXTREME  HD

                                                                                                                    SEVERE  HD

CAUSES

HD is a complex inherited disease whereby the degree of severity of dysplasia in the parents directly influences the frequency and severity in the pups. Even mild dysplasia in one parent will affect the risk of dysplasia developing in their offspring.
A high energy diet leading to rapid growing or overweight pups has a greater chance of producing dysplasia, especially if the growth spurt occurs at a sensitive time in skeletal and muscular development.
Excessive activity in the young animal, especially if overweight or in the presence of exaggerated joint laxity, can aggravate dysplasia.
Calcium intake may be an important factor with both excessive or insufficient calcium being detrimental to joint development.
 

SIGNS OF HD 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".


Breeding from HD free dogs will not necessarily guarantee that their offspring will be HD free.

 An HD control programme in Sweden showed that:

Normal to Normal matings produced 18% dysplastic offspring.

Normal to Dysplastic matings produced 59% dysplastic offspring.

Dysplastic to Dysplastic matings produced 87% dysplastic offspring.

CONCLUSION

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.


REFERENCES

Hip Dysplasia: Understanding the Condition and its Treatment; Dr Race Foster and Dr Marty Smith.

Canine hip Dysplasia: Cheryl Minnier.

Canine Hip Dysplasia in South Africa: Dr Mark Rubinsohn.  

CANINE HIP DYSPLASIA (CHD)
by T. J. Dunn, Jr. DVM

FOOTNOTE

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".

by T. J. Dunn, Jr. DVM                              

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