The Hip Dysplasia (HD) Dilemma
Hip Dysplasia is the most common orthopaedic problem seen in dogs. It is a complex condition with a polygenic inheritance pattern. Environmental factors such as over feeding and over exercising play a role in its development.
It affects
1. Young dogs from 4-12 months causing pain and lameness.
2. Older dogs causing arthritis
Why is it a problem?
1. Affected dogs develop arthritis & lameness
2. It is an inherited problem
3. Breed clubs, Veterinarians, and the VCA worry about it.
4. Screening radiographs are a hassle and cost to breeders and owners.
5. The breeding guidelines of elimination schemes can be confusing.
6. Elimination schemes do not seem to be working.
7. HD causes conflict with in breed clubs
Do we need to worry about it?
Yes:
• It causes lameness and arthritis pain in dogs.
• It causes unhappy puppy buyers.
• We should be able to breed it out, eg Greyhounds
No:
• A lot of show dogs with HD do not show lameness or pain
• Some breeders ignore it and it doesn't affect their kennels success
How should we rank the importance of HD in our Breeding programs?
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1. Temperament |
7. Epilepsy |
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2. Conformation |
8. CLAD |
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3. Coat quality |
9. Heart disease |
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4. Entropian / Ectropian |
10. OCD |
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5. PRA |
11. Elbow Dysplasia |
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6. Fertility |
12. Hip Dysplasia |
We can only select for 2-3 genetic traits at any one time. We need to prioritise the characteristics we are selecting for.
The Rottweiler club selects on hips, elbows, eyes, teeth, conformation and temperament.
GSDC is similar.
These are clubs that have large numbers of dogs to select from.
They can be aggressive in selecting the parameters they choose to use to select which dogs they will breed from.
Dog clubs with smaller numbers must be careful not to put into place any disease elimination program which may exclude large numbers of dogs.
HD Elimination Plans
1. Decide if we wish to eliminate HD completely from the breed.
2. Decide if we wish to reduce the level of HD with in the breed.
3. Set up a scheme which will not disadvantage many (if any) breeders.
4. Have a transparent scheme, understanding that we are all pulling towards the same direction.
Currently available Schemes
1. AVA
2. OFA
3. Other National Schemes
4. PennHIP
AVA scheme
This scheme uses a protocol set out by the British Veterinary Association (BVA) The dogs must be given a general anaesthetic and correctly positioned on their backs.
It measures 9 parameters:
The first 2 of which are related to the laxity of the hips
The other 7 of which are related to degenerative joint changes, (arthritis)
Each parameter is scored out of 6 with a total of 106 points being the highest score possible.
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HIP JOINT |
RIGHT |
LEFT |
COMMENT |
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Norberg angle |
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Subluxation |
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Cranial acetabular edge |
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Dorsal acetabular edge |
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Cranial effective acetabular rim |
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Acetabular fossa |
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Caudal acetabular edge |
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Femoral head/neck exostosis |
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Femoral head recontouring |
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TOTAL |
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Total Score (max 106) |
| Laxity Assessments | |||
| Ortolani's Sign | |||
| Barden's Manouvre | 1. Up to 2mm: 2. 2-5 mm: 3.>5mm: |
The system is also used in Canada, New Zealand and South Africa.
It is the system Dr Malcolm Willis developed for use in German Shepherds. The dogs must be at least 12 months old.
OFA
The Orthopaedic Foundation for Animals (OFA) uses the same positioning as AVA. The OFA requires dogs to be 24 months old.
The OFA does not give a score but rates dogs as excellent, good or fair, all of which are registered.
Borderline dogs are re radiographed in 6-8 months and reassessed then. Dogs with HD are graded mild, moderate or severe.
Other National Schemes
Various European and Scandinavian countries have schemes based on the same BVA positioning. Scoring and assessing varies between countries and there may be marked variation between countries.
Problems with the AVA system
1. Positioning can change the result.
- Dogs held firmly in a wedge may score lower for laxity than those not held firmly
- Dogs whose hips and knees are tied together may score lower than those not tied.
2. In adequate anaesthesia.
- Dogs which are only heavily sedated or very lightly anaesthetised will tighten their hip muscles when the hips are extended and pull the hips back into the sockets, reducing the laxity.
3. Joint capsule tightens in the normal positioning view and may reduce the laxity
4. Age:
- Younger dogs are less likely to show signs of arthritis than older dogs.
- Older dogs are more likely to have a higher score than younger dogs due to arthritis changes.
5. Reader variation.
Individual readers may award different scores for the same dog
6. Must wait until the dog is at least 12 months old before we get a score
7. The true laxity of the hip joints is not always revealed.
8. Low heritability
- The heritability of this system is about 0.2. That means that if we rely on the score to be a measurement of the genetic make up of the dog it is only 20% accurate.
- In a controlled study with 53 litters of Golden Retrievers the estimate of heritability of OFA / AVA type subjective hip scoring was 0.221, and this was not statistically different from 0.
Heritability
Genotype
Genetic makeup
Phenotype
Phenotype
What you look like Genotype + Environment
A heritability of 0.2 (or 20%) means that only 20% of the phenotype is due to the genetic make up. This is one chance in 5 that the characteristic we are selecting for will be expressed in the pups.
PennHIP
PennHIP was developed in 1983. www.vet.upenn.edu
It must be carried out under general anaesthesia uses a different positioning to the AVA system.
3 radiographs are required.
1. The standard AVA view which is used to assess for any arthritic changes.
2. A compressed view wherein the hips are firmly pressed into the hip socket
3. A distracted view where in the hips are firmly pushed out of the sockets.
PennHIP measures the laxity of the hips, in a quantitative manner.
Other laxity assessments such as Barden's manouvre and Ortolani's sign only give a guide as to the presence of laxity but there is no direct measurement.
PennHIP uses a parameter termed the Distractive Index (DI), to measure this laxity. The DI has found to be strongly inherited.
The greater the laxity of the hips the greater the chance of developing arthritis For a GSD with a DI of 0.8 or more the chance of arthritis developing is 100%. Rottweilers have less chance of developing arthritis at any given DI compared to GSD.
Benefits of PennHIP
1. Can be done from 20 weeks onward.
2. The DI does not vary significantly with time. It is highly repeatable, & this repeatability is better at 12 months than at 6 months than at 4 months.
3. The measurements are mathematical and so all readers return the same results.
4. Dogs with HD as determined by the presence of arthritis are documented.
5. Heritability of the DI is very high.
- In the GSD it is 0.61
- In Labradors it is 0.46
- In Golden retrievers it is 0.64
The Distractive Index is the best phenotype that can be tested to predict whether a dog will develop hip arthritis.
Elimination of HD
To eliminate HD from a breed an aggressive program utilising the PennHIP scheme must be adopted.
To continue to use the current AVA / BVA scheme will result in the status quo remaining and no improvement will be made.
Club plans
Any plan must have a long term view.
It will take many generations to reduce and eliminate HD.
All club members are encouraged to participate.
No member should be disadvantaged during the initial stages.
Upper limits of acceptable scores are to be set.
These limits to be bi-annually reviewed and reset as needed.
Breeders to be encouraged to adhere to these limits BUT no breeder should be censured for breeding outside these limits.
Breeders who breed with dogs outside the limits should understand the consequences of such breedings and undertake to progeny test the offspring at 16 20 weeks utilising PennHIP.
They then should select only the tight hipped pups to go on with in their breeding program.
No pups should be sold unless both parents have been hip scored.
Copies of the hip scores must be made available to the club.
Copies of both parents' scores should be provided to each puppy purchaser. Potential purchasers can then assess whether they should purchase pups from sires and dams with high hip scores.
Dogs in the scheme must be positively identified (by microchip or tattoo).
Breeders may have their choice of either AVA or PennHIP systems.
Breeders are encouraged to appreciate the greater accuracy of PennHIP and to utilise it in preference to the AVA system.
Because the 2 schemes measure different parameters they cannot be directly compared.
BUT the following applies
• Good PennHIPs will have good AVA scores.
• Poor PennHIPs may have good or bad AVA score.
• Good AVA score may have good or bad PennHIP score.
At any AVA or PennHIP assessment both Barden's and Ortolani's laxity assessments should be carried out and recorded by the Veterinarian taking the radiographs.
All imported dogs should have a PennHIP or OFA / BVA assessment before entering the country, or prior to breeding.
A PennHIP or OFA / BVA assessment should be obtained from all dogs whose semen is imported into the country.
Any male or female who sires / whelps 5 or more litters, or 20 or more pups should have a PennHIP assessment.
This is because these dogs are having a significant influence on the breed and their true genetic merit (as determined by the DI ) must be known.
Acceptable scores
• Dogs will be considered to have acceptable hips for breeding purposes provided it achieves a score that is equal to or less than the breed average.
• The English Setter breed average is determined from the PennHIP database or the AVA database.
• As of July 2004 the PennHIP breed average is 0.61 with a range of 0.24 - 1.09 based on 394 dogs.
• The AVA breed average is 20.4
BUT:
• For breeding purposes the combined AVA scores of any 2 dogs to be breed with should not be greater than 1.5 times the breed average.
• PennHIP advises breeders to breed with dogs whose DI is lower than their dog's DI.
When using AVA system some allowance must be made for young dogs having potentially poor hips but no arthritis developed at the time of radiographing.
Dogs with a combined laxity scores (Norberg Angle and subluxation) of greater than 14 should not be breed with.
Summary
1. We can do something positive about reducing HD
2. PennHIP provides a useful tool to do this.
3. The AVA system should be used with caution.
4. All club members should embrace a new system which has definite long term goals.
5. No member should be disadvantaged with a new system.
