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.

                Good Hips                                          Dysplastic Hips

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 deeply 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 product 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 considerably lower than the true incidence as the vast 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.

Below are hip x-rays of Cavaliers showing most of the grades of classification. I don’t have a copy of a Borderline or a Severe. You can find examples from other breeds online if you are interested. You can easily see in each x-ray how there is less and less coverage of the head of the femur (the femoral head—the round ‘ball’ at the ‘top’ of the leg bone) and the acetabulum (the ‘cup’ where the femoral head sits) gets more shallow as the status of the hips declines until they barely overlap at all. In a severe there is basically no overlapping whatsoever.

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 in the breed more quickly.

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.

For more information on hip dysplasia, please see some of the following websites:

www.ofa.org/
This is the official OFA website which offers excellent information as well as a database where you can look up a specific dog (or kennel name) and see for yourself if it has been certified.

www.vet.upenn.edu/pennhip/
This explains the PennHIP method of evaluating for hip dysplasia.

The following are the only acceptable result forms for hip dysplasia in the USA:

Below is the OFA Hip Clearance Form

NOTE O.F.A. NUMBER ON FORM
KCS-4105E28F-NOPI is the OFA number
E indicates an *Excellent* rating
28 is the age in months at evaluation
F is the gender of the dog
PI means the dog has permanent identification (microchip/tatoo)
NOPI means the dog does not have permanent identification (the dog did in this case but the vet forgot to put it on the form! That problem was rectified so dog could get her CHIC form.)

Next is the OFA Preliminary Consultation Report. Something similar is used if there is evidence of hip dysplasia.

Last is the PennHIP Evaluation Form

As an interesting comparison, the following is a picture of the x-ray of the same dog, this time submitted to OFA for evaluation. OFA evaluated her hips as *Fair*.

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PATELLAR LUXATION or dislocating kneecap(s) can be inherited, or acquired through trauma.  It occurs sporadically among Toy breed dogs, although it can be found in large breeds.

In dogs the patella is a small bone which protects the front of the stifle joint; it is the counterpart of the kneecap in humans.  It is anchored in place by ligaments, and slides in a groove in the femur.

Conditions which predispose to patellar luxation are:  a shallow groove, weak ligaments; and mal-alignment of the tendons and muscles that straighten the joint. The patella may slip inward (medial luxation) or outward (lateral luxation).  Luxating patellas in toy breeds are most commonly found to luxate medially.  Lateral luxation is most commonly caused by trauma, although in some cases it can also be inherited.

The signs of patellar luxation are difficulty straightening the knee; pain in the stifle; and a limp. Often a dog with patellar luxation will look somewhat stiff in that leg because the dog is attempting to use muscles to *lock* it so the patella won't move around as much.

The diagnosis is confirmed by a regular veterinarian who manipulates the stifle joint and is able to push the kneecap in and out of position without excess force.

There are 4 grades of patellar luxation:

(1) Intermittent patellar luxation causing the limb to be carried occasionally.

(2) Frequent patellar luxation which, in some cases, becomes more or less permanent.

(3) The patella is permanently luxated with torsion of the tibia and deviation of the tibial crest of between 30 degrees and 50 degrees from the cranial/caudal plane.

(4) The tibia is medially twisted and the tibial crest may show further deviation medially with the result that it lies 50 degrees to 90 degrees from the cranial/caudal plane.

Grades (1) and (2) can often be controlled by keeping the dog lean, on a good diet (supplements may help as well), and not allowing excessive jumping. A Grade 2 can tighten to a Grade 1 and often a Grade 1 can tighten until there is no patellar luxation at all. They can also get worse.

Grades (3) and (4) nearly always need surgery to deepen the groove and/or realign or tighten the ligaments.

Any licensed veterinarian can manipulate and check for patellar luxation. X-rays are not necessary.   

The following are some acceptable test result forms for patellar luxation in the USA. 

OFA Application form the veterinarian fills out which can be sent to OFA for an official registration number and certificate. 

This is the OFA official patellar luxation clearance form a breeder receives back after sending in the filled-out Application form.

NOTE THE O.F.A. NUMBER ON FORM
KCS-PA2241/28F/P-NOPI is the OFA number
28 is the months in age at evaluation
F is the sex of the dog
PI means the dog has Permanent Identification
NOPI means the dog does not (again in this case vet forgot to put no. on application!)