Hip Dysplasia
 

HIP DYSPLASIA is a common cause of rear-end lameness in the dog.  The problem lies in the structure of the joint.  The head of the femur (thigh bone) should sit solidly and tightly in the acetabulum (cup).  In hip dysplasia loose ligaments allow the head to begin to work free.  A shallow acetabulum also predisposes to joint laxity.  Finally, the mass or tone of the muscles around the joint socket is an important factor.

Tight ligaments, a broad pelvis with a well-cupped acetabulum, and a good ratio of muscle mass to size of bone, predispose to good hips.  The reverse is true of dogs who are likely to develop the disease.  Environmental factors, including weight and nutrition of the puppy and rearing practices figure into the final outcome.  Keeping a growing puppy lean and on a good diet will greatly mask and may even prevent the symptoms of hip dysplasia.

Above are examples of hip x-rays of two different Cavaliers .  If you compare the two you can see that the hip sockets on the right x-ray are not as deep as those on the left x-ray therefore the femoral heads do not sit as deep into the sockets--more of the femoral head is left out of the socket.  Also in the dysplastic x-ray you can see the circled hip is much worse than the other hip.  The end of the femoral head is already worn down.  Because of stress, the area pointed to behind the femoral head has filled in so much the indentation is nearly gone.  Compare this to the other three hips that have good indentation behind the femoral head.  NOTE:  the dog with the dysplastic hips showed NO signs of hip dysplasia when walking or running.  The x-ray was taken only because the owner wanted to make sure the dog did not have hip dysplasia before it was bred.  Since the dog does have hip dysplasia, the breeder decided not to breed the dog.  Also BOTH parents are OFA clear of hip dysplasia, and so is the one other sibling whose hips have been x-rayed and sent to OFA.

Hip dysplasia is a moderately heritable condition.  It is more likely among littermates having a dysplastic parent, but even dogs with normal hips can produce dysplastic pups.  However--consistently breeding unaffected dogs WILL reduce the incidence of hip dysplasia, especially if the hip status of littermates is taken into consideration.

According to OFA statistics, approximately 10-11% of all Cavaliers develop hip dysplasia by 2 years of age.  Please note that this figure is lower than the true incidence as the majority of breeders do NOT send in x-rays that show obviously dysplastic hips.  The widely accepted guess is that the incidence is probably about twice as high as what the OFA statistics show.  Again, this is a developmental defect.  Puppies are NOT born with hip dysplasia.  Some dogs with x-ray evidence of even severe hip dysplasia show NO clinical signs (no pain or lameness), so the disease may remain entirely unsuspected unless an x-ray is taken to check for it.

OFA uses the following method of classifying hip dysplasia.  A clear x-ray of the hips is taken and sent to OFA for evaluation.  Preliminary x-rays (taken before the dog is age 2) are evaluated by one radiologist.  Permanent x-rays (taken after the dog is 2 years old) are evaluated by three radiologists who have to come to an agreement on the status of the hips.  Hips declared free of hip dysplasia are assigned either an Excellent, Good or Fair rating.  There is a Borderline Conformation/Intermediate classification in which they normally ask that the dog be x-rayed again at a later date for re-evaluation.  Hips that are dysplastic are rated as Mild, Moderate or Severe.  OFA suggests that only dogs FREE of any signs of hip dysplasia in the x-rays should be used for breeding.

PennHIP uses an entirely different way of evaluating hips.  They have the vet take 3 different x-rays in 3 different positions to check for laxity of the hip joints.  A number is assigned to each hip stating the amount of laxity found. PennHIP then publishes the *average* hip scores for that particular breed.  They suggest that only dogs that have laxity scores in the *better* half should be used for breeding.   Obviously although the aim is at improving the hip status of offspring, some dysplastic dogs may be able to be used for breeding under the PennHIP approach, especially in breeds prone to a lot of hip dysplasia.  This is a more controversial approach, but their hope is that laxity is the prime reason for the development of hip dysplasia and using dogs with the lower laxity scores may possibly bring about improvement more quickly.  Time will tell.

Treatment for hip dysplasia is directed at relieving pain and improving function by giving aspirin or one of the newer products used in the treatment of degenerative joint disease.  If pain cannot be controlled there are surgical procedures which may relieve pain and improve function in some individuals.

Breeders who follow the InfoCenter Principles test all breeding stock for hip dysplasia BEFORE breeding. 

Provided with written permission from INFOSITE