BVA / Kennel Club hip dysplasia scheme

Hip dysplasia (HD) is a condition of the hip joint characterized by instability of the joint. It is generally considered that puppies are born with a normal conformation of the joint but that laxity or instability of the joint develops early in life. The mechanism for the development of laxity is largely genetically mediated but is influenced by environmental factors. These include the size and breed of the dog, its rate of growth, type of feeding, and the type and duration of exercise.

The hip is a ‘ball-and-socket’ joint, the ball being the head of the thigh bone or femur, and the socket being part of the pelvis called the acetabulum. In good hips the femoral head is smoothly rounded and fits tightly and deeply into the acetabulum.

With constant activity of the puppy, the lax hip may become painful due to the development of inflammatory joint disease secondary to the instability. Initially there will be inflammation of the joint and thickening of the joint capsule which will encourage stabilization of the joint.

As the condition progresses, new bone called osteophytes develops along the joint margins and muscle development is delayed because of disuse and/or pain. However, by the time the dog is adult, the hip muscles will usually increase in development and add to the secondary stability of the joint.

As the puppy reaches skeletal maturity the joint becomes more stable but its range of motion will be reduced in comparison with a normal dog due to the arthritic new bone. Changes then progress much more slowly during the life of the dog. Their rate depends on the weight of the dog and the type and duration of its activity. However, the consequence of such changes is the development of osteoarthritis. In general, the more lax the joint, the more severe the arthritis is likely to become. 

The BVA/KC Hip Dysplasia Scheme was introduced in 1965 to identify affected dogs and to provide advice to breeders in order to reduce the prevalence of the condition which can have serious effects on the health, behavior and welfare of dogs. Hip radiographs of any breed of dog (including non-registered animals and crossbreds) may submitted to the scheme. Nevertheless, the scheme is particularly recommended for those breeds where hip dysplasia is common.

Some common breeds at risk are:

• Bernese Mountain Dog
• German Shepherd
• Golden Retriever
• Goldendoodle
• Labrador Retriever
• Labradoodle
• Newfoundland
• Rottweiler 

Submission to the scheme is a two stage process. The first stage involves your veterinarian taking radiographs of your dog’s hips. Dogs must be at least one-year-old but there is no upper age limit. The dog’s KC registration certificate and any related transfer certificates must be available so that the appropriate details can be printed on the radiograph. Additionally your veterinarian will also check your dog’s microchip/tattoo numbers which will also be printed on the radiographs.

Dogs will need to be sedated or anesthetized so appropriate arrangements should be made with your veterinarian. The dog is positioned on its back with its hind legs fully extended. Frequently, radiographs are taken for the hip and elbow dysplasia scheme at the same appointment. Payment for the radiographs is made to your veterinarian.

Owners should sign the declaration (first part) of the certificate, to verify the details of the dog are correct and grant permission for the use of the results.

The second stage involves submission of the radiographic images by your veterinarian to the BVA together with the scoring fee made (payable to the BVA) and the part-completed certificate of grading. The veterinary surgeon submitting the X-ray certifies that the X-ray was taken on the date indicated and the dog’s identity is correct.

The radiographic images are examined by two panellists who assess them using a scoring scheme. Panellists are appointed annually by the BVA and each year they undertake a quality assurance exercise to ensure consistency of interpretation.

Nine radiographic features of each hip are evaluated with points being given for preordained changes. Scores of the nine features are added to give a total score for each hip. The lower the score the less the degree of HD present. The minimum (best) score for each hip is zero and the maximum (worst) is 53, giving a range for the total score of 0 to 106.

The scrutineers complete the certificate and sign it. It is then returned to the submitting veterinarian together with the radiographs if they are not digital images.

Once a certificate has been issued further radiographs of the dog may not be submitted for regrading. Owners may appeal against the original grade but these must be lodged with the BVA, in writing, within 45 days of grading. The original radiographic images and an appeal certificate must be submitted by the owner’s veterinarian to the BVA. These will be reviewed by a second pair of panellists and re-graded by the Chief Scrutineer whose decision will be final.

Occasionally radiographic images submitted to the scheme are rejected because they cannot be scored accurately. This may be due to technical problems with the image or inaccurate positioning of the hips. Scrutineers must be confident that the grade they give is correct and if there are features that are open to misinterpretation it is in the dog’s interest that better images are submitted. Incorrect identification of the patient will also result in return of the radiograph and certificate for the error to be corrected.

Hip scoring should be considered along with other criteria as part of a responsible breeding programme, and breeders should choose breeding stock with hip scores around and ideally below the breed median score. The median score is calculated from all the scores recorded for that breed over the previous five years and is the middle score of the population, ie 50% of dogs have a lower score and 50% have a higher score.

Infrequently, offspring may be affected even though both parents had low scores. This is discouraging but it should be remembered that a random assortment of genes will occasionally result in a disappointing genotype. Such disappointment can be reduced by considering the dam and sire’s Estimated Breeding Values (EBVs) to determine the genetic risk for each dog passing the disease to their offspring. EBVs are a more accurate indicator of genetic risk than using an individual dog's hip score alone.

EBVs link all available pedigree information with data collected through the BVA/KC hip dysplasia scheme. The information on relatives (who share genetics) influences the genetic risk of an individual. Therefore, the more dogs that are scored under the scheme, the more accurate the EBV will be. This is reflected in the confidence of the EBV which is an indication of how much scoring information has been used to calculate the EBV. The more scoring information available, from the dog itself and/or its relatives, the greater the confidence that the EBV is close to the actual genetic risk.

A dog's EBV can change during its lifetime, either upward or downward, as more information becomes available, either about the dog itself, or its relatives. Ideally breeders should use dogs that that have an EBV which is lower than average (ie a minus number), and preferably with a confidence rating of at least 60%.

Dogs with an EBV which is higher than average can still be bred from with care, providing they are mated to a dog with an EBV which is well below average (assuming that the confidence for both dogs is high). If a dog with less than an ideal hip score, but a low EBV that has a good confidence, is bred from, its offspring should be carefully monitored and preferably they should be hip scored themselves. 

EBVs are available on the Kennel Club website under MateSelect (https://www.thekennelclub.org.uk/services/public/mateselect/Default.aspx). Due to limited available data, not all breeds have published EBVs.