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Hip dysplasia certification schemes (US)

Hip dysplasia certification schemes (US)

Dysplasia is the abnormal development of a structure, in this instance the hip joint. This malformation of the joint often leads to degenerative or arthritic changes in mature animals. Futhermore, x-ray changes do not always mean the animal will have clinical signs of lameness. Nonetheless, most veterinary specialists would recommend x-rays and assessment of family histories of disease in dogs prior to breeding in an effort to reduce the incidence of this condition. Hip dysplasia certification schemes have been introduced to identify dogs at an early stage so that they can be prevented from breeding and passing the condition to their puppies. These schemes have been widely adopted by several breed societies.

What are the signs of hip dysplasia?

Hip dysplasia is a common and often debilitating joint disease affecting many larger breed (usually pedigree) dogs. Affected dogs have a genetic tendency to develop the disease but the severity of the disease can be influenced by other factors. Most affected dogs appear normal when young but develop clinical signs in middle and older age as arthritis develops. Severely affected young dogs may show hind leg weakness and lameness. Dogs may be obviously lame if one hip is more severely affected than the other but many dogs have similar changes in both hips. This means they do not ‘favor’ one leg over the other and just appear generally stiff. Dogs may exhibit a bunny-hopping gait and often resist joint flexion/extension maneuvers performed by clinicians. Sometimes owners do not recognize the problem, even though their pet may be in continuous discomfort.

What causes hip dysplasia?

The normal hip joint is a smoothly fitting ball-and-socket joint. The top of the thigh bone is smooth and round and fits tightly into a cup-shaped depression in the pelvis. The underlying cause is a laxity of the soft tissues supporting the hip joint so that the joint surfaces rub together instead of gliding smoothly over one another. Hip dysplasia is present from a very young age when the bones are still not fully developed and therefore soft. The hip joint fails to develop properly and abnormal stress on the joint causes the formation of arthritic new bone. The process becomes a vicious circle, exacerbated by obesity and over-exercise.

Hip dysplasia is not caused by a single factor. Some dogs are more likely to develop hip dysplasia because of their genetic make-up. It is thought that some factors in the way the dog is brought up (such as feeding and exercise) can also influence the development of the disease.

How can hip dysplasia be prevented?

The only way to eliminate this condition is to avoid breeding from affected animals. However in many breeds most individuals are affected and so selective breeding, ie breeding from those individuals with less severe disease is required. The Orthopedic Foundation for Animals (OFA) has developed a hip dysplasia scoring scheme that classifies the severity of disease in individuals. Identification of affected individuals allows for selective breeding.

Hip dysplasia can also be assessed using the PennHIP scoring scheme (www.pennhip.org).

What is the OFA hip certification scheme?

Scoring x-rays is similar to judging at dog shows – standard criteria are laid down but the same dog may not win under different judges nor even under the same judge on different occasions. It is well recognized that the Scoring Scheme has limitations and is not foolproof:

  • It cannot detect dogs with reasonable hips but which are carrying hip dysplasia genes.
  • It cannot take into account environmental factors such as body weight.
  • It takes no account of the dog’s age (except that all dogs x-rayed must be at least 1 year of age).

Radiographic assessment is largely subjective and prone to differences in opinion between the scrutineers.

How are x-rays taken for hip assessment?

In the OFA scheme a single x-ray is used to assess a dog’s hips. The dog is positioned on its back with its back legs fully extended. This position is best achieved in the relaxed dog using sedation or general anesthesia and artificial restraint (ie sandbags or ties to maintain the legs in the correct position). It is a common misconception that correct positioning requires the dog’s legs to be held during the x-ray – this is very dangerous for the handler and is not necessary. The film should be identified before processing with the dog’s registration number, the date, the veterinarian’s name or hospital name, and a left or right marker.

For PennHIP scoring 3 x-rays are required.

What happens to the x-rays?

OFA scheme

When a diagnostic radiograph has been obtained, it is submitted to the OFA together with the scoring fee and a part-completed certificate of scoring. The owner fills in the top of the certificate, with the dog’s details and pedigree information. The veterinary surgeon submitting the radiograph certifies that the radiograph was taken on the date indicated, and must check and add the dog’s microchip or tattoo number so that the OFA can forward information to the AKC. The x-ray is examined by 3 board-certified veterinary radiologists (from a panel of scrutineers) who assess the hips and decide whether any changes are present. The final score is a composite of the 3 radiologists’ scores.

PennHIP scheme

A PennHIP score is given by specially trained veterinarians – you can find a local PennHIP veterinarian. The fee for taking and assessing x-rays is paid to the veterinarian who takes the x-rays. The x-rays are sent to the PennHIP analysis center for evaluation.

Why was my dogs x-ray returned without scoring?

A small percentage of radiographs submitted for certification under the OFA scheme are rejected because they cannot be scored accurately. Accurate positioning is essential to give a correct score. If the pelvis is rotated and the hips are very good then the overall score may appear to be higher (worse) than it really is, and this unfairly penalizes the dog, especially if the breed is generally low scoring.

Occasionally factors relating to the quality of the x-ray result in rejection. X-rays that are improperly exposed or processed will be too pale or too dark, resulting in loss of contrast and definition. If the features cannot be assessed then a score cannot be given. Incorrect identification of the patient will also result in return of the radiograph as the certificate that assigns a particular score to a specific individual cannot be signed if the scrutineer cannot guarantee that the x-ray they are looking at belongs to a particular dog.

It is unlikely that x-rays for the PennHIP scheme would be unsuitable for evaluation as veterinarians are specially trained in taking these x-rays.

How does the scheme help to prevent hip dysplasia?

The most helpful way of using the scoring information is in progeny testing. This means selecting parents which are known to have previously produced puppies with good hips as well as having low hip scores themselves. It is important to investigate the hip scores of as many offspring of individual dogs as possible before selecting them for further breeding. It is also helpful to breed dogs whose grandparent’s scores were low. If it were possible to prevent any dogs that carry the gene for hip dysplasia from producing puppies then the disease could be eradicated.

The OFA recommends:

  • Breeding from dogs with normal hips.
  • Breeding normals with normal ancestry.
  • Breed normals from litters with low incidence of HD.
  • Use sire that produces few puppies with HD.

If you are thinking of buying a pedigree puppy find out if hip dysplasia is likely in your chosen breed and enquire about the hip score status of the parents before considering purchase. This can reduce the risk of hip dysplasia developing in your puppy although it is still possible for two parents with very low hip scores to produce puppies with hip dysplasia. It is theoretically possible for people who purchase dogs that are subsequently found to have HD to sue breeders who have bred from affected parents.

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